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.
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.
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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:
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.
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
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.
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
Syntax:
fl <sec>
where:
<sec> is the duration of the intense flash.
Example: 0.7 second intense flash
fl 0.7
Syntax:
fl <sec>
where:
<sec> is the duration of each of the alternating flashes.
Example: 0.25 second flash
fl 0.25
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
Syntax:
ec <sec>
where:
<sec> is the duration of the eclipse.
Example: Eclipse for 4 seconds
ec 4
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
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
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°)
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 lighthouses have obstructions. 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.
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:
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
o – Oil
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.
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.