Glossary

Terms and Abbreviations

Arc of visibility   The start and ending degrees for a angle where light can be seen.
Characteristic   Describes how the light emanating from a lighthouse can be recognized visually.
Coordinates   The latitude and longitude of a lighthouse.
Direction light   A light showing over a very narrow sector, forming a single leading light. This sector may be flanked by sectors of greatly reduced intensity, or by sectors of different colors or character.1
Duration   Length of time in seconds that light may be shown or not shown (eclipsed).
Geographical range   The maximum distance at which light from a light can theoretically reach an observer as limited only by the curvature of the earth and the refraction of the atmosphere, and by the elevation of the light and the height of eye of the observer.2
Latitude   An angular distance of any point on the surface of the earth north or south of the equator. The equator is latitude 0°, and the North Pole and South Pole are latitudes 90°N and 90°S, respectively. The length of one degree of latitude averages about 69 mi (110 km); it increases slightly from the equator to the poles as a result of the earth's polar flattening. Latitude is commonly determined by means of a sextant or other instrument that measures the angle between the horizon and the sun or another celestial body, such as the North Star (see Polaris). The latitude is then found by means of tables that give the position of the sun and other bodies for that date and hour.3
Light character   Part of the characteristic that defines the pattern of light only.
Light list   Excerpts from published light lists are displayed on these web pages. The information extracted from each published light list, on a per light basis, are the lighthouse name, coordinates of the lighthouse, characteristic, structure description, optic, fog signal, radiobeacon, and reference number. Also extracted are all the radiobeacons and special radio direction finders, whether or not they are associated with a light. The light list may have typos that could have later been corrected in notices to mariners. Most errors were left in anyway; that is, don't assume that what appears to be incorrect on the website was incorrectly presented on the website!
Longitude   An angular distance on the earth's surface measured along any latitude line such as the equator east or west of the prime meridian. A meridian of longitude is an imaginary line on the earth's surface from pole to pole; two opposite meridians form a great circle dividing the earth into two hemispheres. By international agreement, the meridian passing through the original site of the Royal Greenwich Observatory at Greenwich, England, is designated the prime meridian, and all points along it are at 0° longitude. All other points on the earth have longitudes ranging from 0° to 180°E or from 0° to 180°W. The international date line lies along the 180° meridian. Meridians of longitude and parallels of latitude together form a grid by which any position on the earth's surface can be specified.4
Modern replacement   A lighthouse that has been replaced by a modern-type structure (what is viewed as modern is subjective). The original 'classic' structure may or may not still exist. Tracking modern replacement lights through the light lists after the classic lighthouse was deactivated could be challenging for the following reasons: 1) the light name changed, 2) the established date was no longer included in light lists some time in the mid-1980s (very important), 3) the coordinate was no longer being displayed since the modern light became a minor light (also very important). It is possible due to these difficulties that some currently operational modern lights today could have fallen between the cracks because it was too difficult to track and, thus were not extracted from later light lists.
Nominal range   Luminous range of a light in nautical miles when the meteorological visibility is 10 nautical miles.5
Occulting light   A light in which the total duration of light in a period is longer than the total duration of darkness, and the intervals of darkness (eclipses) are usually of equal duration.6
Period   All lights other than fixed lights exhibit a sequence of intervals of light and darkness, the whole sequence being repeated identically at regularly intervals. A period is the time taken to exhibit one complete sequence.7
Published light list   A publication that contains a list of lights, sound signals, buoys, daybeacons, and other aids to navigation. They typically include a unique reference number, aid name (i.e., lighthouse name, etc.), coordinates, characteristic and intensity, elevation of the light, nominal range for the light, a description of the structure and possible height, and remarks such as sectors, arcs of visibility, etc. for each aid to navigation. The "Admiralty Charts and Navigations - Vol. A-L" and "United States Coast Guard Light List - Vol. I-VII" are current light list publications.
Quick light   A light which flashes at a rate of not less than 50 flashes per minute but less than 80 flashes per minute.8
Range lights   Two or more lights associated so as to form a leading line to be followed.9 Also known as leading lights.
Reference number   A unique identifier that is used to represent an aid to navigation in a published light list. NOTE: A published light list might actually reference a light in multiple sections of the light list and, thus, have multiple reference numbers for the same light. Within this website, only one reference number will be shown.
Sector light   A light presenting different appearances, either of color or character, over various parts of the horizon of interest to maritime navigation.10

Lighthouse Coordinates

The location of each lighthouse can be defined by its coordinates, consisting of the latitude and longitude. The user can view the coordinates for each lighthouse by accessing the Light Lists link or by accessing a map through either the USA Map or Map Lists links and positioning the cursor over a small rectangle in the middle of a lighthouse's characteristic arc.

The syntax for the latitude is the following:

Ndd mm.fff

where:

N = a constant representing the northern hemisphere (should always be this in the USA).

dd = degrees number (0-89).

mm = minutes number (0-59).

fff = fractional minute (0-999).

The syntax for the longitude is the following:

Wddd mm.fff

where:

W = a constant representing the western hemisphere (should always be this in the USA).

ddd = degrees number (0-179).

mm = minutes number (0-59).

fff = fractional minute (0-999).

The syntax for coordinates is simply concatenating the latitude and longitude together, separated by a space. For example, N32 40.302 W117 14.454 (Old Point Loma Lighthouse in California) are valid coordinates.

Characteristics

A characteristic describes the light and its pattern that emanate from a lighthouse. The textual representation of a characteristic as displayed in these web pages is broken into the following sections where each section is separated by a period:

Base light pattern – the characteristic type, light colors, and period.

Light distances – on light lists prior to 1973, the geographical range each color of light can be seen in nautical miles; on light lists after 1972, the nominal range each color of light can be seen in nautical miles. This information may be omitted if the published light list does not specify this information, but it is defined for a majority of the characteristics. If the light distances are not known, a default distance of 6 nautical miles is used when displaying the arc on the area maps.

Flash/eclipse durations – the amount of time in seconds where the light may be on or off. This information may be omitted if it is not applicable (e.g., a fixed light does not have durations) or is not contained in the published light list.

Sectors – contains the color and angle of each sector of light. This information is omitted if the light does not have sectors.

Obstructions – contains the angle of each obstruction of light. This information is omitted if the light does not have obstructions. This information may actually be listed as arcs of visibility in published light lists.

For example, suppose a lighthouse has a fixed light with white and red sectors, the white light can be seen for 20 nautical miles, the red light can be seen for 16 nautical miles, a red sector from 000°-050°, a white sector from 050°-125°, and a red sector from 125°-150°. The characteristic would be as follows:

F WR. W20 R16. R000°-050°(050°), W050°-125°(075°), R125°-150°(025°).

As another example, suppose a lighthouse has a group flashing white light that flashes for 0.2 second, eclipses for 1.8 seconds, flashes for 0.2 second, eclipses for 1.8 seconds, flashes for 0.2 second, eclipses for 5.8 seconds, and has an obstruction from 075°-100°. The characteristic would be as follows:

Fl(3) W 10s. (fl 0.2, ec 1.8) x 2, fl 0.2, ec 5.8. Obstructed 075°-100°(025°).

The remainder of this page describes the different parts of a characteristic in more detail.

Base Light Patterns

Fixed

Syntax:

F <color>

where:

<color> is the color of the light (may be combined into sectors):

W – White

R – Red

G – Green

Y – Yellow

NOTE: The above colors are applicable whenever referenced as <color> on this page.

Description:

A light showing continuously and steady.

Examples:

Characteristic Description
F W Fixed white light
F R Fixed red light
F WR Fixed light with white and red sectors

Sample Illustration:

Fixed With Flash

Syntax:

FFl <color> <sec>

where:

<color> is the color of the light:

<sec> is the characteristic period.

Description:

A light in which a fixed light is combined with a flashing light of higher luminous intensity.

Examples:

Characteristic Description
FFl W 30s Fixed white light with higher intensity white flash every 30 seconds

Sample Illustration:

Flash

Syntax:

Fl <color> <sec>

where:

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A flashing light in which a flash is regularly repeated (at a rate of less than 50 flashes per minute).

Examples:

Characteristic Description
Fl W 5s Flashing white light every 5 seconds
Fl WG 2.5s Flashing light every 2.5 seconds with white and green sectors

Sample Illustration:

Group Flash

Syntax:

Fl(<group-num>) <color> <sec>

where:

<group-num> is the number of flash groups in the period.

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A flashing light in which a group of flashes, specified in number, is regularly repeated.

Examples:

Characteristic Description
Fl(3) W 15s Three grouped white flashes every 15 seconds
Fl(2) WR 5s Two grouped flashes every 5 seconds with white and red sectors

Sample Illustration:

Composite Group Flash

Syntax:

Fl(<group1-num> + <group2-num>[ + <groupN-num>]) <color> <sec>

where:

<group#-num> is the number of flashes in each flash group separated by a plus sign.

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A light similar to a group flashing light except that successive groups in a period have different number of flashes.

Examples:

Characteristic Description
Fl(1 + 4 + 3) W 45s Three grouped white flashes, the first with 1 flash, the second with 4 flashes, and the third with 3 flashes every 45 seconds

Sample Illustration:

Long Flash

Syntax:

LFl <color> <sec>

where:

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A single-flashing light in which an appearance of light of not less than two second duration (long flash) is regularly repeated.

Examples:

Characteristic Description
LFl WRG 6s Long flashing light every 6 seconds with white, red, and green sectors

Sample Illustration:

Alternating Flash

Syntax:

AlFl <colors> <sec>

where:

<color> is the color combination of the light:

<sec> is the characteristic period.

Description:

A flashing light in which a group of multi-color flashes is regularly repeated.

Examples:

Characteristic Description
AlFl WR 10s White flash followed by a red flash every 10 seconds

Sample Illustration:

Alternating Fixed Flash

Syntax:

Alf <color1> Fl <color2> <sec>

where:

<color1> is the color of the fixed light.

<color2> is the color of the flashing light.

<sec> is the characteristic period.

Description:

A light in which a fixed light is combined with a flashing light of a different color.

Examples:

Characteristic Description
AlF W Fl R 60s Fixed white light with with a red flash every 60 seconds

Sample Illustration:

Quick (Continuous) Flash

Syntax:

Q <color>

where:

<color> is the color of the light (may be combined into sectors):

Description:

A quick light in which a flash is regularly repeated.

Examples:

Characteristic Description
Q W Continuous white quick flash
Q WG Continuous flash with white and green sectors

Sample Illustration:

Quick Group Flash

Syntax:

Q(group-num) <color> <sec>

where:

<group-num> is the number of flash groups in the period.

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A quick light in which a specified group is regularly repeated.

Examples:

Characteristic Description
Q(5) W Five quick flashes followed by an eclipsed duration
Q(9) WG Nine quick flashes with white and green sectors followed by an eclipsed duration

Sample Illustration:

Isophase

Syntax:

Iso <color> <sec>

where:

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A light in which all the durations of light and darkness (eclipse) are equal.

Examples:

Characteristic Description
ISO R 6 Red light is on for 3 seconds and off for 3 seconds
ISO WR 10 Light with white and red sectors that is on for 5 seconds and off for 5 seconds

Sample Illustration:

Occulting

Syntax:

Oc <color> <sec>

where:

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

An occulting light in which an eclipse is regularly repeated.

Examples:

Characteristic Description
Oc W 8 White light is on for more than 4 seconds and off for less than 4 seconds
Oc WG 10 Light with white and green sectors that is on for more than 5 seconds and off for less than 5 seconds

Sample Illustration:

Group Occulting

Syntax:

Oc(<group-num>) <color> <sec>

where:

<group-num> is the number of flash groups in the period.

<color> is the color of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

An occulting light in which a group of eclipses, specified in number, is regularly repeated. The total duration of light in each period may be equal to the total duration of darkness.

Examples:

Characteristic Description
Oc(3) R 15 Group of three occulting red light durations that occur in 15 seconds

Sample Illustration:

Alternating

Syntax:

Al <color> <sec>

where:

<color> is the color combination of lights.

<sec> is the characteristic period.

Description:

A continuously steady light which shows a change in color.

Examples:

Characteristic Description
Al WG 10 White light is on for 5 seconds then green light is on for 5 seconds

Sample Illustration:

Morse Code

Syntax:

Mo(<chars>) <color> <sec>

where:

<chars> are the Morse Code character(s) represented in the characteristic.

<color> is the color combination of the light (may be combined into sectors):

<sec> is the characteristic period.

Description:

A light in which appearances of light of two clearly different durations are grouped to represent a character or characters in the Morse Code.

Examples:

Characteristic Description
Mo(K) W 20 Morse Code character ‘K’ is represented with white light every 20 seconds

Sample Illustration:

Flash/Eclipse Durations

The flash and/or eclipse durations define the length of flashes or the length of eclipses, in seconds or fractions of seconds, in more detail, and its format is based on the characteristic type but is not applicable to all characteristic types. However, the flash and/or eclipse durations are not always contained in a light list for the applicable characteristic types and will be omitted when displaying the characteristic for that light in this case.

Flash

Syntax:

fl <sec>

where:

<sec> is the duration of the flash.

Example 1: 0.5 second flashing light

fl 0.5

Example 2: 1 second flashing light

fl 1

Fixed With Flash

Syntax:

fl <sec>

where:

<sec> is the duration of the intense flash.

Example: 0.7 second intense flash

fl 0.7

Alternating Flash

Syntax:

fl <sec>

where:

<sec> is the duration of each of the alternating flashes.

Example: 0.25 second flash

fl 0.25

Group Flash

Syntax (two groups only):

fl <flash-sec>, ec <eclipse-sec1>, fl <flash-sec>, ec <eclipse-sec2)

where:

<flash-sec> is the duration of each flash.

<eclipse-sec1> is the duration of the eclipse for the first group.

<eclipse-sec2> is the duration of the eclipse for the last group.

Example: 0.5 second flash; 2 second eclipse; 0.5 second flash, 7 second eclipse

fl 0.5, ec 2, fl 0.5, ec 7

Syntax (more than two groups):

(fl <flash-sec>, ec <eclipse-sec1>) x <groups-1>, fl <flash-sec>, ec <eclipse-sec2)

where:

<flash-sec> is the duration of each flash.

<eclipse-sec1> is the duration of each eclipse for the first “groups minus one” groups.

<eclipse-sec2> is the duration of the eclipse for the last group.

Example: 3 groups: 0.25 second flash, 1.75 second eclipse; 4th group: 0.25 second flash, 3.75 second eclipse

(fl 0.25, ec 1.75) x 3, fl 0.25, ec 3.75

Occulting

Syntax:

ec <sec>

where:

<sec> is the duration of the eclipse.

Example: Eclipse for 4 seconds

ec 4

Group Occulting

Syntax:

(ec <eclipse-sec>, lt <light-sec1>) x <groups-1>, ec <eclipse-sec>, ec <light-sec2)

where:

<eclipse-sec> is the duration of each eclipse.

<light-sec1> is the duration of each light for the first “groups minus one” groups.

<light-sec2> is the duration of the light for the last group.

Example: 2 groups: eclipse for 1 seconds, light for 3 seconds; 3rd group: eclipse for 1 seconds; light for 7 seconds

(ec 1, lt 3) x 2, ec 1, lt 7

Group Quick Flash

Syntax (two groups only):

fl <flash-sec>, ec <eclipse-sec1>, fl <flash-sec>, ec <eclipse-sec2)

where:

<flash-sec> is the duration of each flash.

<eclipse-sec1> is the duration of the eclipse for the first group.

<eclipse-sec2> is the duration of the eclipse for the last group.

Example: 0.2 second flash; 0.5 second eclipse; 0.2 second flash, 4.1 second eclipse

fl 0.2, ec 0.5, fl 0.2, ec 4.1

Syntax (more than two groups):

(fl <flash-sec>, ec <eclipse-sec1>) x <groups-1>, fl <flash-sec>, ec <eclipse-sec2)

where:

<flash-sec> is the duration of each flash.

<eclipse-sec1> is the duration of each eclipse for the first “groups minus one” groups.

<eclipse-sec2> is the duration of the eclipse for the last group.

Example: 2 groups: 0.2 second flash, 2.8 second eclipse; 3rd group: 0.2 second flash, 8.8 second eclipse

(fl 0.2, ec 2.8) x 2, fl 0.2, ec 8.8

Light Distances

No matter what type of characteristic a lighthouse may have, an active lighthouse always displays light! However, depending on the year of the light list, the meaning of the light distances listed on them may be different.

Up to 1972, the light distances are listed as the geographical range. This is a theoretical maximum distance that is only limited by the curvature of the earth, the refraction of the atmosphere, and the elevation of the light. However, it does not account for other conditions that can greatly influence the distance the light can be seen.

After 1972, the light distances are listed as the nominal range. The distance at which lights are sighted varies greatly with atmospheric conditions and this distance, expressed in nautical miles, may be increased by abnormal atmospheric refraction. It will be reduced by fog, haze dust, smoke, or precipitation; a light of low intensity is easily obscured by any of these conditions and the sighting range of even a light of very high intensity is considerably reduced in such conditions. For this reason, the nominal range of a light should always be considered when estimating the range at which it may be sighted, bearing in mind that varying conditions may exist between the observer and the light. Typically non-white lights such as red or green have a smaller nominal range then white lights. Green glass robs the illuminating power of a light of about 80 percent of its intensity, and red glass does the same by about 58 percent. 11

NOTE: The U.S. Coast Guard actually listed both the geographical and nominal ranges on their light list several years prior to 1973, but discontinued showing the geographical range in 1973.

NOTE: In many cases where the characteristic has sectors, only a single light distance is specified in the light list. Undoubtably, the light distances are not actually all the same value for each different color, particularly when one of the colors is white. This is more obvious when the candlepower of each light color, which is not included in the research, is noted in the light lists. However, since the light distance for each color is not known, the distances are assumed to be the same when listed on this website!

Sometimes in the Remarks column of many light lists, it was mentioned that light intensities could be less in certain areas; mostly this was true with range lights where the intensity of the light may be less outside the range line. If the light distance and sectors of these diminished intensitities were not specifically described, it will not be reflected in the characteristic displayed on this website.

When displayed in a characteristic, light distances are displayed immediately to the right of the light character. However, the light distance is not always contained in a light list and will be omitted when displaying the characteristic for that light in this case. The following shows how the light distance (nominal range) is displayed in a characteristic:

<color1><miles1>[,<color#><miles#>]

where:

<color> is the color of the light:

<miles> is the nautical miles the light can be seen.

For example, the following describes a lighthouse with one light color (white) that can be seen for 10 nautical miles:

W10

As another example, the following describes a lighthouse with five sectors but only three distinct colors, one color being white that can be seen for 20 nautical miles, the second color being red that can be seen for 17 nautical miles, and the third color being green that can be seen for 17 nautical miles:

W20, R17, G17

Geographic Range Table18

The following table gives the approximate geographic range of visibility for an object which may be seen by an observer whose eye is at sea level; in practice, therefore, it is necessary to add to these a distance of visibility corresponding to the height of the observer's eye above sea level.

Distances of visibility for objects of various elevations above sea level.

Height (feet) Distance (nautical miles)   Height (feet) Distance (nautical miles)   Height (feet) Distance (nautical miles)
5 2.6   70 9.6   250 18.1
10 3.6   75 9.6   300 19.8
15 4.4   80 10.2   350 21.4
20 5.1   85 10.5   400 22.9
25 5.7   90 10.9   450 24.3
30 6.3   95 11.2   500 25.6
35 6.8   100 11.4   550 26.8
40 7.2   110 12.0   600 28.0
45 7.7   120 12.5   650 29.1
50 8.1   130 13.0   700 30.3
55 8.5   140 13.5   800 32.4
60 8.9   150 14.0   900 34.3
65 9.2   200 16.2   1000 36.2

Meteorological Optical Range Table19

Code No. Weather Range
0 Dense Fog Less than 50 yards
1 Thick Fog 50-200 yards
2 Moderate Fog 200-500 yards
3 Light Fog 500-1000 yards
4 Thin Fog ½- 1 nautical miles
5 Haze 1-2 nautical miles
6 Light Haze 2-5½ nautical miles
7 Clear 5½-11 nautical miles
8 Very Clear 11-27 nautical miles
9 Exceptionally Clear Over 27 nautical miles
 
From the International Visibility Code

Luminous Range Diagram20

This diagram will enable the mariner to determine the approximate range at which a light may be sighted, at night, in the meteorological visibility prevailing at the time of observation.The diagram is entered from the top or bottom border, using the nominal range listed in column 4 of this book (i.e., the light list). The figures along the curves represent the estimated meteorological visibility at the time of observation (the International Visibility Code is defined using metric units), and those along the side borders the luminous range under those conditions.

NOTE: The nominal range is used on the website starting in 1973, at which time the geographical range was no longer included in the light lists.

Example: A light having a nominal range of 20 miles. When the meteorological visibilty is 20 miles, the light would be sighted at about 33 miles, given a sufficient elevation of height of eye, and when the visibility is 2 miles, would be sighted at about 5½ miles. Since the scale along the top border is based on a meterological visibility of 10 sea miles, the luminous ranges under the prevailing conditions obtained from the 10-mile curve will be identical to those with which the diagram is entered from the top border. If a line is drawn joining points where the values from the left hand border intersect equal values on the curves, it will be seen to be parallel with and to the right of the curve for perfect visibility. Luminous ranges in the conditions prevailing at the time of obvservation obtained from intersections to the left of this line will be less than the estimated meteorological visibility, while those to the right will be greater. Due to their intensity, many lights will therefore be sighted at a greater distance than that of the estimated meteorological visibility.

The diagram can also be used to obtain an approximate meteorological visibilty. For example, when a light with a nominal range is first sighted at 12 miles, the meteorlogical visibility will be about 5 miles.

CAUTION. - When using this diagram it must be remembered that:

1. The ranges obtained are approximate.
2. The transparency of the atmosphere is not consistent between the observer and the light.
3. Glare from background lighting will reduce considerably the range at which lights are sighted.

Light Considerations24

The condition of the atmosphere has a considerable effect upon the distance at which lights can be seen. Sometimes lights are obscured by fog, haze, dust, smoke, or precipitation which may be present at the light, or between it and the observer, but not at the observer, and possibly unknown to him. On the other hand, refraction may often cause a light to be seen farther than under ordinary circumstances. A light of low intensity will be easily obscured by unfavorable conditions of the atmosphere and less dependence can be be placed on its being seen. For this reason, the intensity of a light should always be considered when expecting to sight it in thick weather. Haze and distance may reduce the apparent duration of the flash of a flashing light. In some circumstance of the atmosphere, white lights may have a reddish hue. Colored lights are more quickly lost to sight under weather conditions which tend to reduce visibilty than are white lights.

It should be remembered that lights placed at great elevations are more frequently obscured by clouds, mist, and fog than those near sea level.

In regions where ice conditions prevail in the winter, the lantern panes of unattended lights may become covered with ice or snow, which will greatly reduce the visibility of the lights and may also cause colored lights to appear white.

The increasing use of brilliant shore lights for advertising, illuminating bridges, and other purposes, may cause marine navigatonal lights, particularly those in densely inhabited areas, to be outshone and difficult to distinguish from the background lighting. Mariners are requested to report such cases as outlined above in order that steps may be taken to improve the conditions.

The "loom" of a powerful light is often seen beyond the limit of visibility of the actual rays of the light. The loom may sometimes appear sufficiently sharp to obtain a bearing.

At some distances, some flashing lights may show a faint continuous light between flashes.

It should be borne in mind that, when attempting to sight a light at night, the range of vision is considerably increased from aloft. By noting a star immediately over the light, an accurate compass bearing may be indirectly obtained on the light from the navigating bridge although the light is not yet visible from that level.

The distance of an observer from a light cannot be estimated by its apparent intensity. Always check the characteristics of lights in order that powerful lights visible in the distance shall not be mistaken for nearby lights showing similar characteristics at low intenstity (such as those on lighted buoys).

If lights are not sighted within a reasonable time after prediction, a dangerous situation may exist requiring prompt resolution or action to insure the safety of the vessel.

The apparent characteristic of a complex light may change with the distance of the observer. For example, a light which actually displays a characteristic of fixed white varied by flashes of alternating white and red (the phases having a decreasing range of visibility in the order; flashing white, flashing red, fixed white) may, when first sighted in clear weather, show as a simple flashing white light. As the vessel draws nearer, the red flash will become visible and the characteristic will apparently be alternating flashing white and red. Later, the fixed white light will be seen between the flashes and the true characteristic of the light finally recognized - fixed white, alternating flashing white and red (F. W. Alt. Fl W. and R.).

There is always a possibility of a light being extinguished. In the case of unattended lights, this condition might not be immediately detected and corrected. The mariner should immediately report this condition. During periods of armed conflict, certain lights may be deliberatly extinguished without notice if the situation warrants such action.

Emergency lights. Emergency lights of reduced intensity are displayed from many major light stations when the main and stand-by lights are extinguished; these emergency lights may or may not have the same characteristic as the main light. The characteristic of the emergency lights are listed in column (7) of this publication (i.e., the light list), if characteristic is different from main light.

NOTE: While a light list may specify an emergency light, this information was not extracted from the light list and, thus, is not included on this website.

If a vessel has considerable vertical motion due to its pitching in a heavy sea, a light sighted on the horizon may alternately appear and disappear. This may lead the unwary to assign a false characteristic and hence to err in its identification. The true characteristic will be evident after the distance has sufficiently decreased or it can be determined by increasing the height of eye of the observer.

Sectors of colored glass are placed in lanterns of some lights to produce a system of light sectors of different colors. In general, red sectors are used to mark shoals or to warn the mariner of other obstructions to navigation or of nearby land. Such lights provide approximate bearing information since an observer may note the change of color as he crosses the boundary between sectors. These boundaries are indicated in the Light Lists and by broken lines on the charts. These bearings, as all bearings referring to lights are given as true in degrees from 000° to 359° as observed from a vessel toward the light. Altering course on the changing sectors of a light or using the boundaries between light sectors to determine the bearing for any purpose is not recommended. Be guided instead by correct compass bearing of the light and do not rely on being able to accurately observe the point at which the color changes. This is often difficult to decide because the edges of a colored sector cannot be cut off charply. On either side of the line of demarcation between white and red sectors, and also between white and green, there is always a small arc of uncertain color. Moreover, when haze or smoke are present in the intervening atmosphere, a white sector might have a reddish hue.

The area in which a light can be observed is normally a circle with the light as the center and the range of visibility as the radius. However, on some bearings the range may be reduced by obstructions. In such cases, the obstructed arc might differ with the height of eye and distance. When a light is cut off by adjoining land and the arc of visibility is given, the bearing on which the light disappears may vary with the distance of the vessel from which observed and with the height of eye. When the light is cut off by a sloping hill or point of land, the light may be seen over a wider arc by a ship far off than by one close to.

Circles drawn on charts around a light are not intended to give information as to the distance at which it can be seen, but solely to indicate, in the case of lights which do not show equally in all directions, the bearings between which the variation of visibilty or obscuration of the light occurs.

At many lights rip-rap mounds are maintained to protect the structures against ice damage and scouring action. There have been collisions with the uncharted, submerged portions of such rip-rap by vessels attempting to pass the lights extremely close aboard.

Sectors

Sector lights are used to enable a mariner to determine what may lie within that sector of light; for example, sector lights might mark the entrance to a channel, shoals, underwater obstructions, etc.

The limits of a sector’s arc of visibility are rarely clear cut especially at a short distance, and instead of disappearing suddenly, the light usually fades after the limit of the sector has been crossed. At the boundary of sectors of different color, there is usually a small arc in which the light may either be obscured, indeterminate in color, or white.

In cold weather, and more particular with rapid changes of weather, the lantern glass and screens are often covered in moisture, frost, or snow, and the sector of uncertainty is then considerably increased in width and colored sectors may appear more or less white. The effect is greatest with green sectors and with weak lights. Under these conditions, white sectors tend to extend into colored or obscured sectors, and fixed or occulting lights into flashing ones.12

Sector degree numbers are specified as follows: the 0th degree is due south, the 90th degree is due west, the 180th degree is due north, and the 270th degree is due east. The current U.S. Coast Guard light lists represent the sector degrees this way. The following diagram13 shows an of a sector light which has a white sector from 000°-200°(200°), a red sector from 200°-260°(60°), and green sector from 260°-000°(100°):

When displayed in a characteristic, sectors are displayed immediately to the right of the flash/eclipse durations. Of course only a small percentage of the lighthouses have sector lights. The following shows how sectors are displayed in a characteristic:

<color1><start-degree1>-<end-degree1>(<num-degrees1>), <color2><start-degree2>-<end-degree2>(<num-degrees2>)[,<color#><start-degree#>-<end-degree#>(<num-degrees#>)]

where:

<color> is the color of the sector light:

<start-degree> is the start degree of a sector.

<end-degree> is the end degree of a sector (clockwise from start degree).

<num-degrees> is the number of degrees in a sector.

For example, the following shows a lighthouse with two sectors, the first sector being white starting at 20 degrees and ending at 210 degrees, and the second sector being red starting at 210 degrees and ending at 20 degrees:

W020°-210°(190°), R210°-020°(170°)

As another example, the following shows a lighthouse with four sectors, the first sector being white starting at 20 degrees and ending at 100 degrees 30 seconds, the second sector being red starting at 100 degrees 30 seconds and ending at 200 degrees, the third sector being white starting at 200 degrees and ending at 250 degrees, and the fourth sector being green starting at 250 degrees and ending at 0 degrees:

W020°-100.5°(80.5°), R100.5°-200°(99.5°), W200°-250°(50°), G250°-000°(110°)

Obstructions

IMPORTANT: Within a light list reference description, it might be stated that a light is "partially obstructed". If the actual degree range of the obstruction is not specified, then no mention of the obstruction is included anywhere on this website.

Light is not shown within an obstruction. An obstruction can be simply a blacked out portion of the lantern, or can be blocked by trees, hills, etc. Light lists either specify these blockages as obstructions or as arcs of visibility. Here they are represented as obstructions; that is, they represent the angles of light that cannot be seen.

Obstruction degree numbers are specified as follows: the 0th degree is due south, the 90th degree is due west, the 180th degree is due north, and the 270th degree is due east. The current U.S. Coast Guard light lists represent the obstruction degrees this way.

The following diagram14 shows an arc of visibility from 170°-340°(170°):

Thus, in the above example, there is an obstruction clockwise from 340°-170° (190°).

When displayed in a characteristic, obstructions are displayed immediately to the right of the sectors. Only a small percentage of the researched lighthouses have obstructions described for them in the light lists. The following shows how obstructions are displayed in a characteristic:

<start-degree1>-<end-degree1>(<num-degrees1>)[, <start-degree#>-<end-degree#>(<num-degrees#>)]

where:

<start-degree> is the start degree of an obstruction.

<end-degree> is the end degree of an obstruction (clockwise from start degree).

<num-degrees> is the number of degrees in an obstruction.

For example, the following shows a lighthouse with one obstruction starting at 25 degrees and ending at 100 degrees:

025°-100°(75°)

As another example, the following shows a lighthouse with two obstructions, the first obstruction starting at 155 degrees and ending at 210 degrees 30 seconds, and the second obstruction starting at 350 degrees and ending at 20 degrees:

155°-210.5°(55.5°), 350°-020°(30°)

As an example to show how to convert visibilities to obstructions, suppose a lighthouse has the following listed in a light list for its arcs of visibilities:

Vis 029°-053°(24°) and 224°-228°(4°)

The following obstructions are the conversion of these arcs of visibilities:

053°-224°(171°), 228°-029°(161°)

As can be seen, the first obstruction is determined by taking the end degree of the first visibility and the start degree of the second visibility, and the second obstruction is determined by taking the end degree of the second visibility and the start degree of the first visibility.

Fog Signals

The function of a fog signal in the system of aids to navigation is to warn of danger, and to provide the mariner with a practical means of determinating his position with relation to the fog signal at such times as the station or any visual signal which it displays is obscured from view by fog, snow, rain, smoke, or thick weather. Among the devices that were commonly used as fog signals are:15

Diaphones which produce sound by means of a slotted reciprocating piston actuated by compressed air. Blasts may consist of two tones of different pitch, in which case the first part of the blast is high and the last of a low pitch. These alternate pitch signals are called “tow-tone”.

Diaphragm horns which produce sound by means of a diaphragm vibrated by compressed air, steam, or electricity. Duplex and triplex horn units of differing pitch produce a chime signal.

Reed horns which produce sound by means of a steel read vibrated by compressed air.

Sirens which produce sound by means of either a disk or a cup-shaped rotor actuated by compressed air or electricity.

Whistles which produce sound by compressed air emitted through a circumferential slot into a cylindrical bell chamber.

Bells which are sounded by means of a hammer actuated by hand, by a descending weight, compressed gas, or electricity.

Radiobeacons which broadcast simple dot-and-dash combinations by means of transmitter emitting modulated continuous waves. Marker radiobeacons are of low power for local use only. They operate continuously, and they typically transmit a series of ½ second dashes for part of a 15 or 30 second period followed by a silent period to the complete the cycle.

NOTE: It is believed that the first official radiobeacon was operating in 1921. A 1923 light list was the earliest available light list that contained radiobeacon information. The 1920 light lists did not include radiobeacon information. 1921 or 1922 light lists were not available to determine if they included radiobeacon information. An article in the Winter 1998 issue of "The Keeper's Log" discussing the retirement of George R. Putnam, the Commissioner of Lighthouses, states "the addition of radiobeacons to lighthouses and lightships since 1921, and with other uses of radio bearings is an advance of first importance in safeguarding navigation".

Identification

Fog signals are distinguished by their characteristics as specified for each aid. The characteristic of a fog signal is described by the device used to create the sound, such as a diaphone, siren, bell, etc. The signal characteristic is the phase relationship of the recurring sound emissions. Fog signals on fixed stations and lightships produce a specific number of blasts and silent periods each minute, when operating, to provide positive identification. Fog signals on buoys are generally actuated by motion of the sea and, therefore, do not emit regular signal characteristics, and when the sea is calm, may emit no sound signals.16

Fog Signal Considerations25

Fog signals depend upon the transmission of sound through air. As aids to navigation, they have certain inherent defects that should be considered. Sound travels through the air in a variable and frequently unpredictable manner.

It has been clearly established that:

(a) Fog signals are heard at greatly varying distances and that the distance at which a fog signal can be heard may vary with the bearing of the signal and may be different on occasion.

(b) Under certain conditions of atmosphere, when a fog signal has a combination high and low tone, it is not unusual for one of the tones to be inaudible. In the case of sirens, which produce a varying tone, portions of the blast may not be heard.

(c) There are occasionally areas close to the signal, in which it is wholly inaudible. This is particularly true when the fog signal is screened by intervening land or other obstruction, or on a high cliff.

(d) A fog may exist a short distance from a station and not be observable from it, so that the signal may not be in operation.

(e) Some fog signals cannot be started at a moment's notice.

(f) Even though a fog signal may not be heard from the deck or bridge of a ship when the engines are in motion, it may be heard when the ship is stopped, or from a quiet position. Sometimes it may be heard from aloft though not on deck.

(g) The intensity of the sound emitted by a fog signal may be greater at a distance than in the immediate proximity.

All these considerations point to the necessity for the utmost caution when navigating near land in a fog. Mariners are therefore warned that fog signals can never be implicitly relied upon, and that the practice of taking soundings of the depth of water should never be neglected. Particular attention should be given to placing lookouts in positions in which the noises in the ship are least likely to interfere with hearing a fog singal. Fog signals are valuable as warnings but the mariner should not place implicit reliance upon them in navigating his vessel. They should be considered solely as warning devices.

Emergency fog signals. Emergency fog signals are sounded at some of the light and fog signal stations when the main and stand-by fog signal is inoperative. Some of these emergency fog signals are of a different type and characteristic that the main fog signal. The characteristic of the emergency fog signals are listed in column (7) of this publication (i.e., the light list).

NOTE: While a light list may specify an emergency fog signal, this information was not extracted from the light list and, thus, is not included on this website.

The mariner must not assume:

(a) That he is out of ordinary hearing distance because he fails to hear the fog signal.

(b) That, because he hears a fog signal faintly, he is at a great distance from it.

(c) That he is near to it because he hears the sound plainly.

(d) That the distance from and the intensity of the sound on any one occasion is a guide to him for any future occasion.

(e) That the fog signal is not sounding because he does not hear it, even when close proximity.

Other Signals

Radiobeacon Distance Finding17

At certain stations the radiobeacon and sound signal are synchronized for distance finding. Whenever the sound signal is operating, a group of two radio dashes (a short and long, 1 second and from 3 to 5 seconds respectively) is transmitted at the end of each radiobeacon minute of operation. A group of two sound blasts of corresponding length is sounded at the same time. When within audible range of the sound signal, navigators on vessels with radio receivers capable of receiving the radiobeacon signals may readily determine their distance from the station by observing the time in seconds which elapses between hearing any part of the distinctive group of radio dashes, say the end of the long dash, and the corresponding part of the group of sound blasts, say the end of the long blast, and dividing the result by 5 (or more exactly 5.5) for nautical miles. The error of such observations should not exceed 10 percent.

The 1-second dash preceding the long dash is a stand-by or warning signal as is also the 1-second blast. The later serves as an identification signal to assure the observer that he is taking time on the correct sound signal blast.

For observations on aerial sound signals a watch with second hand is all that is needed, although a stop watch is more convenient.

Observations for distance off at these stations are not restricted to vessels with direction finders, but may be made by any vessel having a radio receiver capable of receiving in the band 285 to 325 kilocycles within which radiobeacons are operated. A loud speaker is desirable although not necessary.

At distance-finding stations, the sound fog signal characteristic and its time relation for synchronization with the radiobeacon is shown by a diagram. An example of the use of these synchronized signals follows: In the case of Boston Lightship if the interval between hearing the end of the long radio dash marking the end of the radiobeacon minute and the end of the long (5-second) blast of the diaphone is 33 seconds, the observer is 33 / 5.5 = 6 miles from the lightship.

IMPORTANT: Depending on the year distance finding information was specified in a light list, this information was presented differently. In the 1940-1961 light lists, a chart was displayed, along with the other pertinent reference information, for each distance finding station that showed an overall three minute period. During the first two minutes, the radiobeacon was silent, and the audible fog signal sounded its characteristic. During the third minute, the radiobeacon was silent for 52 seconds and then transmitted its last eight seconds as described above; the audible fog signal may or may not have sounded in the first 52 seconds of that minute, but sounded in the last eight seconds to synchronize with the radiobeacon. However, in the radiobeacon overview section at the beginning of some later light lists that did not contain detailed distance finding information per radiobeacon (i.e., a chart), this two minute period was displayed in a sample distance finding chart as five minutes. There is no explanation anywhere whether this was actually a two or five minute period. This website assumes that it was always two minutes instead of five, but please keep in mind that it may have been different. After 1961, this distance finding chart was no longer included with each light list reference.

IMPORTANT: Since distance finding information was no longer included in light lists after 1973, it is assumed the distance finding function was no longer supported after 1973.

IMPORTANT: Starting in 1935, a table was included in the light lists which showed the radiobeacon information in tabular form. Starting in 1940, a map was included in the Atlantic coast light lists, along with the radiobeacon table, that showed the location of each radiobeacon on the Atlantic coast, the Gulf of Mexico, and Puerto Rico. This map also included most of the details of the radiobeacon such as its frequency and type. For most years, in a few rare cases, there may have been a discrepency between the map and the table. For 1943 in particular, around when many lightships were temporarily taken out of service during World War II, there were major discrepencies between the radiobeacon map and the table. In these cases, the information from the table was assumed to be correct and reflected as such on the radiobeacon map displayed on this website. Therefore, these discrepencies are not identifed on this website. Additionally, radiobeacon information (not as detailed) is shown for each station (light station, light ship, buoy, or radiobeacon) in the actual light list with the fog signal information. In a few rare circumstances, there may have been a discrepency between this information and the table. In these cases, the information is presented exactly as it was extracted from the light list, so it is possible to notice the discrepency. Furthermore, a radiobeacon map in a light list may show a few radiobeacon stations under construction; if the radiobeacon was not operational, it will not be shown on the website in either the radiobeacon map or table.

Special Radio Direction Finder Calibration Stations21

United States sequenced radiobeacons cannot broadcast at any time other than assigned operating minute for the purpose of enabling vessels to calibrate their radio direction finder calibration transmitters without causing interference. Special radio direction finder calibration transmitters of short range are operated at certain localities to provide continuous calibration service. These stations with information as to position, frequency, characteristic, etc., are listed (in its own section of the light list under "Special Radio Direction Finder Calibration Stations").

NOTE: The "Special Radio Direction Finder Calibration Stations" section of the light list was first introduced in 1950. While radiobeacon stations provided a service for enabling vessels to calibrate their radio direction finders upon request at least as far back as 1935, the concept of the special direction finder calibration stations did not appear until 1950 (may have been as early as 1948, but 1948 and 1949 light lists were not available for research).

The position given for the antenna is the point from which the radiobeacon signal is transmitted.

If it is not practicable to determine the time of calibration sufficient in advance to contact the district commander, request may be made directly to the stations by means of telephone, telegraph, or a whistle signal consisting of three long blasts followed by three short blasts, this whistle signal to be repeated until it is acknowledged by the station through the starting of the transmitter. The same group of signals should be sounded at the termination of calibration.

If attention of station personnel is not attracted by the whistle signals, hoist the international code signal "OQ - I am calibrating radio direction finder..." indicating a request for radio direction calibration.

The work of the station personnel is not confinded to standing watch and there may be times when the signals for calibration are not immediately heard or seen due to the noise from operating station machinery, etc. Usually, a repeated signal not too far from the station will attract attention.

Regular and frequent use of the direction finder under all conditions is one of the best means of insuring ability to obtain accurate bearings and that the direction finder is at all times in proper condition. It is important to determine and record the frequency dial setting of a direction finder for each radiobeacon. In plotting long-range bearings on a chart of the Mercator projection a correction must be made as the line of bearing is not a straight line excepting in the meridian.

Radiobeacons and Direction Finders22

Accuracy of direction finders is dependent upon the skill of the operator, the equipment used, and radio wave interference. Skill in operations of a manual radio direction finder can be acquired only through practice and by following the operating instructions provided with the equipment. An understanding of adverse conditions and direction finding limitations will be an asset to the prudent navigator.

As an operator obtains bearings with a manually revolving loop type direction finder, he can estimate the bearing by the arc of silence (NULL) or minimum strength. Automatic direction finders do not afford this advantage. However, an experienced operator can evaluate the direction finder's performance by the ease and smoothness (lack of jitter) with which the indicator approaches a bearing.

Erroneous radio direction finder bearings may result from the following conditions:

(a) Currents induced in the direction finder antenna by re-radiation from the structural features of the vessel's superstructure and distortion of the radio wave front due to the physical dimensions and contour of the vessel's hull.

(b) Night effect caused by the combination of two radio wave fronts arriving at the receiver simulataneously. One wave travels directly from the transmitter to the direction finder and is called the ground wave. The other is a downcoming radio wave reflected off the ionosphere and is called the skywave. The effect is more predominant around the time of morning and evening twilight, but it remains throughout the night on the low frequency band. On higher frequencies a similar effect exists during the day as well as at night. Beyond normal groundwave range, only the skywave is received.

Bearings taken around the periods of morning and evening twilight and at night should be treated or accepted with doubt as to their accuracy.

Since the skywave itself is complex in nature it should not be used with a conventional direction finder.

(c) Lateral deviation of the radio wave can occur when the great circle route between the transmitter and the receiver is roughly parallel to a coastline or passed over a coastline. Bearings that are within 10 to 15 degrees of a coastline should not be trusted. Likewise, bearings taken when a land mass is between the transmitter and the vessel should be used with caution.

(d) Most direction finders have a vertical sensing antenna to eliminate any possibility of a 180 degree error in reading. Such an ambiguity is possible in all direction finders if the sensing circuits should become inoperative.

Conclusions: Correct direction finder calibration will compensate for errors caused by inducing currents and vessel configuration. The usual method of calibration is to obtain a series of simultaneous radio and visual bearings on a transmitter. This may be done while a ship swings at anchor, or more quickly by steaming in a circle within sight of the transmitting antenna. It is essential that radio direction finders be accurately calibrated; therefore, recalibration should be made after any changes to the ship's structure or rigging or whenever there is reason to believe the previous calibration has become inaccurate. The direction finder should be calibrated by competent personnel.

Before taking bearings on a commercial station broadcasting entertainment programs, the mariner should consider:

(a) The operating frequency of the station may differ widely from the frequency for which the direction finder is calibrated.

(b) The broadcast antenna may be remote from the broadcast station and,

(c) The majority of these stations are inland.

Accordingly, the use of broadcast stations to obtain a direction finder bearing is not recommended.

Due to many factors which go into the transmission and reception of radio signals, a ship cannot estimate with any degree of accuracy its distance from a radiobeacon by the strength of the received signals.

A vessel steering a course for a radiobeacon should observe the same precautions that apply when steering for a light or any other mark. If the radiobeacon is a lightship or off-shore platform, particular care should be exercised to avoid the possibility of collision. Sole reliance should never be placed on sighting the lightship or light station or listening for a fog signal in time to avoid a collision.

As further aid to assure proper direction finder operation, the mariner should check, whenever possible, the accuracy of the direction finder against visual bearings. This will afford the operator practice and confidence in his equipment as well as an operational check of the direction finder itself.

All mariners using U.S. Coast Guard radiobeacon transmissions for navigation of their vessel must understand the limitations of the direction finding equipment and the possible erroneous bearings due to the causes outside the control of the U.S. Coast Guard. In order to understand the limitations and capabilities of his direction finder, the mariner must understand the following definitions:

(a) Sensitivity is defined as a measure of the ability of a receiver to detect transmissions. All direction finder receivers do not have the same sensitivity; some will receive a radiobeacon signal at its rated range while others will not be able to hear the same signal until they are closer to the radiobeacon transmitter. For example, some direction finders have a sensitivity of 75 microvolts per meter on the radiobeacon band which means they are capable of homing on a radio signal whose intensity is 75 microvolts or more. A direction finder, having a sensitivity of 120 microvolts per meter, will be unable to receive a radiobeacon signal rated at 75 microvolts per meter at 100 miles until 56 miles from the radiobeacon station. At 56 miles, the signal strength of the transmitted signal is 120 microvolts per meter, which is equal to the sensitivity of the receiver. From the foregoing, it can be seen that the sensitivity of a direction finder determines the degree to which the full capactity of the radiobeacon system can be utilized. Mariners should bear this fact in mind when selecting equipment.

(b) Selectivity is a measure of the ability of a receiver to choose one frequency and reject all others. The extent of selectivity will vary with the type of receiver and its condition. The transmitted radiobeacon signal is normally composed of two frequencies that are separated by 1020 hertz (i.e,. 286.000 kHz and 287.020 kHz). A direction finder capable of accepting only this narrow band of frequencies would be ideal. If a direction finder accepts a wide band of frequencies (i.e., 280 to 292 kHz when tuned to 286 kHz), it will admit more noise and more undesired signals. This additional interference may reduce the usefullness of the desired signal, and effectively decrease the maximum range of reception of the radiobeacon.

The marine radiobeacon system is based on direction finder selectivity specifications as follows:

Frequency deviation from resonant frequency (kHz) DB below resonance response Approximate signal ratios for rejection of undesired
±2 3 1.4
±3 12 4.0
±4 25 17.5
±6 50 300.0
±9 70 3,000.0
±12 80 10,000.0
* Resonant frequency is that frequency to which the receiver is tuned.

Errors in bearing may result in a radio direction finder if its selectivity is poor. For example: a bearing is desired on a radiobeacon transmitting on 286 kHz and having a field intensity of 75 microvolts per meter at 100 miles. Assume that a ten mile marker radiobeacon is operating on 292 kHz as shown below. The direction finder is located near the extreme service range of both transmitters.

Using the desired selectivity tables shown above, a direction finder, with these characteristics can distinguish between the two frequencies. The desired 286 kHz radiobeacon signal affects the direction finder 300 times more than the undesired marker radiobeacon signal. If the selectivity were half as good, the desired 286 kHz signal would affect the direction finder only four times more than the undesired 292 kHz signal. The resultant bearing obtained would probably be some value between the two radiobeacons.

Differential GPS28

The Coast Guard is implementing a new system for marine navigation called Differential GPS (DGPS). As the newest electronic system of navigation, DGPS transmitters provide offshore coverage and provide all weather electronic aid to navigation capabilities. The Coast Guard operates transmitting stations located on the Atlantic, Gulf, and Pacific coasts as well as on the Great Lakes.

DGPS is the regular GPS with an additional correction (differential) signal added. The differential is determined when the GPS derived position of the reference station is computed and compared with its surveyed geodetic position. The differential signal improves the accuracy of the GPS and can be broadcast over any authorized communication channel to specialized receivers.

DGPS transmitters located at each site will broadcast corrections of the GPS system to users. The corrections are modulated on a DGPS transitter carrier (285-325 kHz band) in the form of Minimum Shift Keying (MSK) modulation. The modulation data rate for any transmitter can be 50, 100, or 200 bits per second (bps).

The ranges of DGPS transmitting sites vary from 35 to 300 nautical miles and are maintained and operated continuously by the U.S. Coast Guard.

Optics

The optic information extracted out of the published light lists is displayed using the following format:

<optic> [<illuminant>]

where:

<optic> is the type of lens:

<lamps> Lamps / <inches> Refl. - Lamps and reflectors where <lamps> is the number of lamps and <inches> is the size of the reflectors in inches.

1st or 1 - First order lens

2nd or 2 - Second order lens

3rd or 3 - Third order lens

3.5 - 3.5 order lens

4th or 4 - Fourth order lens

5th - Fifth order lens

6th - Sixth order lens

<size> mm - where <size> is the focal length of the lens in millimeters (e.g., 150 mm, 200 mm, 250mm, 300 mm, 350 mm, 375 mm)

Dl - Doublet lens

Ll or Lens lantern

Pl or Post lantern

Rg - Range lens

Rf - Reflector

Tubular lantern

<illuminant> is something that can serve as a source of light (optional):

a - Acetylene gas

e - Electric light

iov - Incandescent oil vapor

m - Mantle

o - Oil

sv - Sodium vapor

The optic information displayed on a Lighthouse Light List and Google™ Map page is shown exactly as it was stated in the published light list. That explains why, for example, a first order lens could be “1st” (earlier light lists) and “1 iov” (later light lists). The manufacturers of the optics are not specified in the light lists and, thus, are not displayed in the optic information. Although the candlepower of the light is contained in most of the light lists, this information was not extracted from the light lists and, thus, is not displayed in the optic information.

Daymarks23

In order to completely describe the dimensions, shape or purpose, and color of each type of daymark, a standard designation has been assigned. From this designation a standard description of each type of daymark has been formulated.

Designations:

1. First letter - Shape or purpose


C - Crossing

J - Junction

K - Range

M - Mid-channel

N - No lateral significance

P - Pointer

S - Square

T - Triangle


2. Second letter - Major color


B - Black

G - Green

R - Red

W - White


3. Third letter (range daymarks only) - Color of stripe


4. Additional information required after a dash (-)


- I Intracoastal Waterway

- SY Yellow square on daymark (dual purpose)

- TY Yellow triangle on daymark (dual purpose)

Example: The designation KRW - I indicates a range daymark (K), major color red (R), color of stripe white (W), in the Intracoastal Waterway series (I).

Descriptions:

SW Square shaped white daymark with a green reflective border.
SW-I Square shaped white daymark with a yellow reflective border.
SB Square shaped black daymark with a green reflective border.
SG Square shaped green daymark with a green reflective border.
SB-I Square shaped black daymark with a yellow reflective border.
SB-SY Square shaped black daymark with a green reflective border and a square shaped yellow reflector.
SB-TY Square shaped black daymark with a green reflective border and a triangular shaped yellow reflector.
TR Triangular shaped red daymark with a red reflective border.
TR-I Triangular shaped red daymark with a yellow reflective border.
TR-SY Triangular shaped red daymark with a red reflective border and a square shaped yellow reflector.
TR-TY Triangular shaped red daymark with a red reflective border and a triangular shaped yellow reflector.
JB Square shaped daymark bearing horizontal bands of black and red, black band topmost, and with a green reflective border.
JB-I Square shaped daymark bearing horizontal bands of black and red, black band topmost, and with a yellow reflective border.
JB-SY Square shaped daymark bearing horizontal bands of black and red, black band topmost, and with a green reflective border and a square shaped yellow reflector.
JB-TY Square shaped daymark bearing horizontal bands of black and red, black band topmost, and with a green reflective border and a triangular shaped yellow reflector.
JR Triangular shaped daymark bearing horizontal bands of red and black, red band topmost, and with a red reflective border.
JR-I Triangular shaped daymark bearing horizontal bands of red and black, red band topmost, and with a yellow reflective border.
JR-SY Triangular shaped daymark bearing horizontal bands of red and black, red band topmost, and with a red reflective border and a square shaped yellow reflector.
JR-TY Triangular shaped daymark bearing horizontal bands of red and black, red band topmost, and with a red reflective border and a triangular shaped yellow reflector.
MB Octagonal shaped black and white vertically striped daymark with a white reflective border.
MB-I Octagonal shaped black and white vertically striped daymark with a yellow reflective border.
NB Diamond shaped daymark divided into four diamond shapes which are colored so that the horizontal diamonds are white and the vertical diamonds are black and with a white reflective border.
NB-I Diamond shaped daymark divided into four diamond shapes which are colored so that the horizontal diamonds are white and the vertical diamonds are black and with a yellow reflective border.
NR Diamond shaped daymark divided into four diamond shapes which are colored so that the horizontal diamonds are white and the vertical diamonds are red and with a white reflective border.
NR-I Diamond shaped daymark divided into four diamond shapes which are colored so that the horizontal diamonds are white and the vertical diamonds are red and with a yellow reflective border.
NW Diamond shaped daymark with an orange reflective border and, in the center of the daymark, the words "Danger, Submerged Jetty (or other appropriate words describing the nature of the danger).
PB Black pointer with a green reflector.
PB-I Black pointer with green reflector and a yellow stripe.
PR Red pointer with a red reflector.
PR-I Red pointer with red reflector and a yellow stripe.
KBW Vertical rectangular shaped black daymark with a central white stripe.
KBW-I Vertical rectangular shaped black daymark with a central white stripe and a yellow border.
KBR Vertical rectangular shaped black daymark with a central red stripe.
KBR-I Vertical rectangular shaped black daymark with a central red stripe and a yellow border.
KWB Vertical rectangular shaped white daymark with a central black stripe.
KWB-I Vertical rectangular shaped white daymark with a central black stripe and a yellow border.
KWR Vertical rectangular shaped white daymark with a central red stripe.
KWR-I Vertical rectangular shaped white daymark with a central red stripe and a yellow border.
KRB Vertical rectangular shaped red daymark with a central black stripe.
KRB-I Vertical rectangular shaped red daymark with a central black stripe and a yellow border.
KRW Vertical rectangular shaped red daymark with a central white stripe.
KRW-I Vertical rectangular shaped red daymark with a central white stripe and a yellow border.
CW Diamond shaped white daymark with small diamond shaped green reflectors at each corner.
CR Diamond shaped red daymark with small diamond shaped red reflectors at each corner.

Lightships

The following subsections, which were extracted from various light lists, overview lightships and describe how the mariner should navigate with regard to lightships. It shows how this information was presented to the reader of the light lists from 1945-1982 which was very near the end of the era of lightships.

NOTE: There were many grammar issues found during the extraction; however, the text in the following subsections is documented as was found in the light list.

Lightships (1945)29

Lightships

Lightships under way, or off station, will fly the International Code signal letters “PC” (signifying lightship is not at anchor on her station).

All lightships on station and all vessels relieving station ships will display the International Code signal of the station whenever a vessel is approaching or in the vicinity and there are indications that such vessel is in strange waters or fails to recognize the station, or when the vessel asks for the information.

The International Code signal for each lightship station is stated in this list.

Lightships, where so stated, carry riding lights for the purpose of showing in which direction the ship is riding.

Lights on lightships are displayed from 1 hour before sunset to 1 hour after sunrise and at all times when the sound signal is in operation.

Color of lightships. – All lightships in United States coastal waters, except Ambrose Lightship, are painted red with the name of the station in white on both sides, superstructures are white, mast, lantern galleries, ventilators and stacks are painted buff.

Casualties and near casualties to lightships impose upon the U. S. Coast Guard the obligation to CAUTION all shipmasters that course should invariably be set to pass lightships with sufficient clearance to avoid possibility of collision from any cause and needlessly jeopardizing the safety of lightships and their crew, and that of all navigation dependent on these important aids to navigation. Experience show that lightships cannot be safely used as leading marks to be passed close aboard, but should invariably be left abroad off the course, whenever sea-room permits.

Relief lightships may be placed at any of the lightship stations, and, when practicable, will exhibit lights and sound signals having the characteristics of the station. Relief lightships are painted the same color as the station ships, with the word “RELIEF” in white letters on the sides.

Lightships (1966)30

Lightships

Course should invariably be set to pass lightships with sufficient clearance to avoid the possibility of collision from any cause. Errors of observation, current and wind, effects, other vessels in the vicinity, and defects in steering gear may be, and have been the causes of actual collisions, or imminent danger thereof, needlessly jeopardizing the safety of the lightships and their crew, and that of all navigation dependent on these important aids to navigation. Experience shows that lightships cannot be safely used as leading marks to be passed close aboard, but should always be left broad off the course, whenever searoom permits.

When approaching a lightship or a station on a submarine site, on radio bearings, the risk of collision will be avoided by insuring that the radio bearing does not remain constant.

It should be borne in mind that most lightships are anchored to a very long scope of chain and, as a result, the radius of their swinging circle is considerable. The charted position is the location of the anchor. Furthermore, user certain conditions of wind and current, they are subject to sudden and unexpected sheers which are certain to hazard a vessel attempting to pass close aboard.

During extremely heavy weather and due to their exposed locations, lightships may be carried off station without the knowledge and despite the best efforts of their crews. The mariner should, therefore, not implicitly rely on a lightship maintaining its precisely charted position during and immediately following severe storms. A lightship known to be off station will secure her light, fog signal, and radiobeacon and fly the International Code signal “PC” signifying “Lightship is not at anchor on her station”.

Watch buoys are sometimes moored near lightships to mark the approximate station should the lightship be carried away or temporarily removed and to give the crews and indication of dragging. Since these buoys are always unlighted and, in some cases, moored as much as a mile from the lightship, the danger of a closely-passing vessel colliding with them is always present – particularly so during darkness or periods of reduced visibility.

Lightships (1982)31

Lightships

General. A Lightship is a navigation placed in exposed location where it is impractical to construct a fixed aid to navigation. It provides light, fog, and radiobeacon signal, and is distinguished by the characteristics of its signal in the same manner as other aids to navigation. A Lightship underway, or off station will fly the International Code signal letters “LO” signifying “I am not in my correct position”. When at anchor a lightship shows by day a black ball and by night in addition to the authorized aid to navigation lights, a fixed white anchor light in the forepart of the vessel, prescribed by the Rules of the Roads. Lights on a lightship are displayed from 1 hour before sunset until 1 hour after sunrise and at all times when the sound signal is in operation.

Color and name. The lightship is painted red with the name of the station in white on both sides.

Identification. The Lightship will display the international radio call sign for the station by means of international code signal flags whenever a vessel is approaching or is in the vicinity and there are any indications that such a vessel is in strange waters or fails to recognize the station or whenever a vessel asks for the information. The international radio call sign for the lightship station is stated in the light list.

Caution: Courses should invariably be set to pass lightship with sufficient clearance to avoid the possibility of collision from any cause. Errors of observation, current and wind effects, other vessels in the vicinity, and defects in steering gear may be, and have been the causes of actual collisions, or imminent danger thereof, needlessly jeopardizing the safety of the lightship and its crew, and all navigation dependent on this important aid to navigation.

Experience shows that a lightship cannot be safely used as a leading mark to be passed close aboard, but should always be left broad off the course, whenever searoom permits. When approaching a lightship or a station on a submarine site, on radio bearings, the risk of collision will be avoided by insuring that the radio bearing does not remain constant. It should be borne in mind that a lightship is at anchor to a very long scope of chain and, as a result, the radius of its swinging circle is considerable. The charted position is the approximate location of the anchor. Furthermore, under certain conditions of wind and current, it is subject to sudden and unexpected sheers which are certain to hazard a vessel attempting to pass close aboard. During extremely heavy weather and due to its exposed locations, the lightship may be carried off station without the knowledge and despite the best efforts of its crew. The mariner should, therefore, not implicitly rely on a lightship maintaining its precisely chartered position during and immediately following severe storms. A lightship know to be off station will secure her light, fog signal, and radiobeacon and fly the International Code signal “LO” signifying “I am not in my correct position”.

Station buoys are sometimes moored near the lightship to mark the approximate station should the lightship be carried away or temporarily removed and to give its crew an indication of dragging. Since these buoys are always unlighted and, in some cases, moored as much as a mile from the lightship, the danger of a closely-passing vessel colliding with them is always present – particularly so during darkness or periods of reduced visibility.

Miscellaneous Comments

The following are miscellaneous comments that were gathered during the research:

1 While examining the light lists (for example, the 1982 "Light List - Volume I - Atlantic Coast of the United States - First, Third, and Fifth Coast Guard Districts"), there were some perceived errors and some obvious errors. When putting the information into the website database, the obvious errors were corrected so that the website could work properly. As an example, the digits in a sector degree may have been reversed for a particular characteristic which was easily identifyable as being incorrect. However, you might see items that may appear as though the information was incorrectly displayed on the website. While there may be incorrectly displayed information due to the quantity of information displayed, this assumption cannot be made. That is, every attempt was made to display the information on the website as it was extracted from the light list even though it was known to be incorrect as long as it did not negatively affect the operation of the website. For example, there are a few locations that display the Morse code characters for a radiobeacon transmission that do not actually match the dash/dot pattern displayed! There may be a few places on the website that contain edited remarks to help clarify some of the information; this information is enclosed in brackets and is usually very brief and EXTREMELY limited.
2 Over the years, the description of the light characteristics have changed. A good example is the Deer Island Lighthouse (Massachusetts). The characteristic in 1963 is described as "AlF W Fl R 30s. fl 1." with no eclipses specified; in the case, the website assumes this is a fixed white light followed by a red flash with no eclipses. However, the 1964 light list describes the characteristic as "Alt Oc W, Fl R, 30s. lt 15, ec 7.2, fl 0.6, ec 7.2.' (i.e., the durations and eclipses are specified). More than likely, the two characteristics are the same, but the 1963 characteristic is not explicit. However, the website does not make this assumption.
3 Most of the researched light lists contain information about when the light was established and last rebuilt. This rebuild information is not displayed on the website since it can be very misleading. For example, a new rebuild date may be listed only if the keeper's house was rebuilt. Furthermore, the exact dates seem to change slightly; the established and last built dates may waver a year or two. The established dates used on the website are based on the light list and other resources.
4 The deactivation date for a lighthouse is obviously not listed in a light list. It is assumed to be deactivated if it is no longer in a light list! In some circumstances it may be easy to determine when a light was deactivated if the researched light list years are sequential. However, in most cases, additional resources were used to determine the deactivation date. For some lights (particular minor lights), it is hard to determine when they may have been deactivated. For example, a light may be listed in the 1982 light list but not in the 1987 light list. Obviously, the light was deactivated somewhere between 1982 and 1987. If no other resource can be found that lists its deactivation date, a year typically near the middle of those two lists will be assumed as the deactivation date.
  To add to the confusion, it may be possible that a light might have been included in a light list a year or more after it was actually deactivated! As an example, multiple non-light list resources may state a light was deactivated in 1911 but it still appears on the 1915 light list. In this case, the website is assumed to be 'correct' when in fact it might not be; that is, it will include those additional years when the light may have been actually inactivated. This situation was found to be very rare.
5 Up until very recently, the accuracy of the light list coordinates was not very good, at least compared to exact accuracy that can now be obtained though the Global Positioning System. In addition over the years, the actual coordinates in the light list changed even though it is known the light was not rebuilt or moved. For lighthouses that still exist, the exact coordinates can be determined which may be slightly different than what was listed in the light lists. However, for lighthouses that no longer exist, the coordinates from the light lists must be used; therefore, assumptions about the accuracy are taken, but in most cases the website user should be able to get a pretty good general idea where a light was located.
6 Until some years after the U.S. Coast Guard took over the responsibility of the lights, the names of the lights in the light list were fully stated. However, over the years, many of the minor lights got listed as "LIGHT #", where '#' is a number. It was still possible for many years to make the correlation between the lights through other information presented in the light lists. This determination has gotten much tougher over the more recent years since some of the correlating information, such as the established and last rebuilt dates, is no longer included.
7 For range lights, in some cases the visibility of a light might be described in a light list as being a full 360° with a higher intensity on the range line. However, if the exact degrees for the range line were not specified in the light list, then there is no mention on the website of this condition; that is, there will be no indication that there even was a range line. Additionally, when simulating the characteristic, a full 360° circle may be displayed even if the light list specified it as being Visible in range line or Visible 4 degrees each side of range line since the exact degrees of the arc may not be able to be assumed.
8 There are a few lighthouses that actually displayed two different lights (characteristics) from the same structure during different periods of their existence. However, they might actually have a different focal plane and optic. The displayed focal plane and optic are always for the first light (characteristic), and this information is not presented for the second light (characteristic).
9 Many lighthouses were researched; however, there are probably a few that some of you might think are missing. In all practicality, the lighthouses that are shown on the website will not change for the areas that have been researched so far. There might be just a few added in the future in the researched areas which were very difficult to track during the research (such as the Horseshoe East and West Group Ranges).
10 The exact year when radiobeacons were included in the light lists could not be determined. The library at the USLHS headquarters has light lists for 1920 and 1923. The 1920 light list does not list any radiobeacons, but the 1923 light list does. Therefore, 1923 is the assumed approximate first year of radiobeacon inclusion.
11 The USLHS library does not contain any light lists after 1996. The 2004 light lists were actually available on the U.S. Coast Guard website in 2004. The 2004 light lists do not include radiobeacon or special direction finder calibration station information. Therefore, it is assumed that these functions were no longer included in the light lists sometime between 1996 (there was only one radiobeacon on the Atlantic and Gulf coasts) and 2004. DGPS broadcast stations started to be documented in the light lists in 1995, but it is not if or when these stations became obsolete.
12 As was stated in item #1, every attempt was made to display the information as it was extracted from the light lists. The exception is the light characteristics which are displayed in a consistent (normalized) modern day format in order for the website to function properly and to avoid confusion.
13 There are instances where a lighthouse was listed in a light list as being authorized or building. It is assumed at the time the light list was published, these lighthouses were not operational and, thus, are not listed on the website in these cases even if it was possible that the lighthouses were made operational during the year.
14 Some light stations may have been fog signal stations before lighthouses were added to them. The fog signal information displayed is for only those years when the lighthouse was operational (i.e., a lightstation) and is not displayed for those years in which it was strictly a fog signal station.
15 Some of the Pacific coast researched light lists had updates (Notices to Mariners) either marked or pasted in them; that is, the changes that occurred to the lights or light stations, such as a change in the light or fog signal characteristic, were identified that were made before the next light list was published. This website does not contain the updates that were identified in the light lists. More than likely, the changes became part of a subsequent light list.
16 The 1839 light list did not show the characteristic for a number of lighthouses that were contained in the light list and were known to be operational during that year. In this case, these lighthouses are not viewed as being in the light list on the website. Thus, when displaying the characteristic or structure/optic information for one of these lighthouses, it will state that the light list was missing when in fact it was not fully described in the light list.
17 Testing of the functions within the U.S. Light Lists website was performed on the following browsers:
 
Browser Version Comments
Internet Explorer 8.0 Characteristic arcs on an area map page will NOT be identified. Please upgrade to the latest version of the browser.
Internet Explorer 9.0 When hovering over a radiobeacon symbol on a radiobeacon map, the first or second line in the popup may wrap.
Chrome 17.0 No issues.
Safari 5.1.2 Testing using this browser on Windows had problems when accessing Google™ Maps. However, it appears that Apple is no longer supporting this browser on Windows operating systems. Whether there are problems using it on a Mac is unknown. It is HIGHLY recommended to use another modern browser on Windows.
Firefox 10.0.2 No issues.
Opera 9.26 Characteristic arcs on an area map page will be improperly displayed. Please upgrade to the latest version of the browser.
Opera 11.61 No issues.
Netscape 9.0.0.6 AOL has stopped support of the browser. The Light Lists resource may not work as expected. It is HIGHLY recommended to use another modern browser.
  The characteristic simulation appears to work reasonably well on the fairly recent versions of the browsers listed except where noted. Internet Explorer requires version 9 to work properly, and the latest and greatest versions of all browsers seem to work the best. That is, the simulation seems to keep in time with the actual elapsed time much better.
18 The coordinate for the Clinton Harbor radiobeacon in the 1982 and 1987 light lists is listed as 41 16 00 and 73 31 10. However, this coordinate is not correct since that coordinate is too far away from the water and not at the same position as the displayed map in the light list), so it was adjusted to 41 16 00 and 72 31 10.

Footnotes:

1,2,5,7,9 Admiralty List of Lights and Fog Signals- Vol A 2004/05, (Somerset, UK: The United Kingdom Hydrographic Office), x.

3 "Answers.com", 01 Feb. 2007 <http://www.answers.com/topic/latitude>.

4 "Answers.com", 01 Feb. 2007 <http://www.answers.com/topic/longitude>.

6,8 Admiralty List of Lights and Fog Signals- Vol A 2004/05, (Somerset, UK: The United Kingdom Hydrographic Office), xii.

10 "TerraX.org", Glossary of Boating Terms, 01 Feb. 2007 <http://www.terrax.org/sailing/glossary/gs.aspx>.

11-12 "General information sheet about NZ lights", 01 Feb. 2007 <http--www.hydro.linz.govt.nz-lights-lights-general-info.pdf>, 110.

13-14 "General information sheet about NZ lights", 01 Feb. 2007 <http--www.hydro.linz.govt.nz-lights-lights-general-info.pdf>, 118.

15 List of Lights and Other Marine Aids - Atlantic Coast - 1957, (Treasury Department, United States Coast Guard), IX

16 List of Lights and Other Marine Aids - Atlantic Coast - 1957, (Treasury Department, United States Coast Guard), IX

17 List of Lights and Other Marine Aids - Atlantic Coast - 1957, (Treasury Department, United States Coast Guard), XIV

18 Light List - Volume I - Atlantic Coast of the United States - 1975, (Department of Transportation, United States Coast Guard), VI

19 Light List - Volume I - Atlantic Coast of the United States - 1970, (Department of Transportation, United States Coast Guard), VII

20 Light List - Volume I - Atlantic Coast of the United States - 1975, (Department of Transportation, United States Coast Guard), VIII

21 Light List - Volume I - Atlantic Coast of the United States - 1974, (Department of Transportation, United States Coast Guard), XIX

22 Light List - Volume I - Atlantic Coast of the United States - 1974, (Department of Transportation, United States Coast Guard), XIV-XV

23 Light List - Volume I - Atlantic Coast of the United States - 1974, (Department of Transportation, United States Coast Guard), VII

24 Light List - Volume I - Atlantic Coast of the United States - 1974, (Department of Transportation, United States Coast Guard), XII-XIII

25 Light List - Volume I - Atlantic Coast of the United States - 1975, (Department of Transportation, United States Coast Guard), XII

28 Light List - Volume I - Atlantic Coast of the United States - 1996, (Department of Transportation, United States Coast Guard), XXII

29 Light List – Atlantic and Gulf Coasts of The United States - 1945, (Treasury Department, United States Coast Guard), 7

30 Light List – Volume II – Atlantic and Gulf Coast of The United States - 1966, (Department of Transportion, United States Coast Guard), IX-X

31 Light List – Volume I - Atlantic Coast of The United States - 1982, (Department of Transportion, United States Coast Guard), XI-XII