Although divers rarely venture out at night, a basic understanding of lighting sequences could prove very valuable indeed, especially in bad light
Lighting sequences
The total period of a flashing light sequence is from the beginning of one light sequence through the total sequence (not just one part of a multiple sequence) to the beginning of the next sequence.
Chart Symbol |
Legend Description |
|
F |
Fixed (steady light) |
|
Oc |
Occulting (total duration of light more than dark) |
|
Oc(2) |
Group occulting |
|
Oc(2+3) |
Composite group occulting |
|
Iso |
Isophase (light and dark are equal) |
|
Fl |
Flashing (total duration of light less than dark) |
|
Fl(3) |
Group flashing |
|
Fl(2+1) |
Composite flashing |
|
L Fl |
Long Flashing (flash is 2 seconds or longer) |
|
Q |
Quick (50 to 79 per minute) |
|
Q(3) |
Group quick |
|
IQ |
Interrupted quick |
|
VQ |
Very Quick (80 to 160 per minute) |
|
VQ(3) |
Group Very Quick |
|
IVQ |
Interrupted Very Quick |
|
UQ |
Ultra Quick (more than 160 per minute) |
|
IUQ |
Interrupted Ultra Quick |
|
Q(3) |
Group of three quick flashes |
|
W,R,G,Bu,Vi,Y |
White, Red, Green, Blue, Violet, Yellow |
|
30s |
30 seconds to cover light sequence, including darkness |
|
12m |
Height in meters above MHWS or MHHW or where there is no tide above MSL. |
|
23/22M |
Visibility in nautical miles. Now show luminous (or nominal) range. i.e. in this example White is 23 miles, Red is 22 miles. The geographical range of lights can be found in the table of Admiralty List of Lights. |
|
Mo (letter) |
Morse code. |
|
F Fl |
Fixed and flashing. |
|
Al. WR |
Alternating White and Red. |
|
W |
White. |
|
R |
Red. |
|
G |
Green. |
|
Bu |
Blue. |
|
Vi |
Violet. |
|
Y |
Yellow. |
|
Or |
Orange. |
|
Am |
Amber. |
|
90s |
Period in seconds. |
|
12m |
Elevation of light given in metres. |
|
15M |
Light with single range. |
|
15/10M |
Light with two different ranges. |
|
15-17M |
Light with three or more ranges. |
|
(hor) |
Horizontally disposed |
|
(vert) |
Vertically disposed |
Examples
| Fl R 35m 20M |
Fixed red light 35m above MHWS visible at 20 miles. |
| Fl 5s 20m 30M |
Flashing light every five seconds 20m above MHWS visible at 30 miles. |
| Fl (2) G 5s |
Flashing in groups of two, green with 5 seconds delay. |
| VQ (3) 5s |
Very quick flashing in groups of three with 5 seconds delay between groups. |
| Fl (3) WRG 15s 13m 7-5m |
Flashing in groups of three, white red and green. 15 seconds from first flash (including three flashes plus period of darkness), 13m above MHWS, visible from 7nM for white light, 5nM for red and green. |
|
|
