Sidelights
noun
Definition of Sidelights
Sidelights are the red and green navigation lights visible head on and from the side on a boat that is underway at night (from sunset to sunrise). They shine directly ahead in an unbroken arc of 112.5° on either side of the boat and are only visible to approaching vessels.
The two colors of sidelights indicate the side of the boat they’re on:
- Red navigation light: Denotes the port or left side of the boat
- Green navigation light: Indicates the starboard or right side of the boat
Going back to the light angle, in order to achieve an unbroken arc of the horizon of 112.5°, each side light shines dead ahead to 22.5° abaft the beam (behind the widest part of the boat).
Here’s an illustration to help visualize this:
Another determining factor of sidelights is the size and type of boat, let’s break down these requirements in the table below.
| Boat Type | Boat Length In Feet | Side Light Required | Visibility Distance Of Light In Nautical Mile |
| Sailboat (under sail) | Under 23 ft | Sidelights recommended but not required | 1 NM |
| 23–65 ft | Sidelights separate or a bi-colored combination light | 1 NM | |
| Alternatively, tri-color light (red, green, white) on top of the masthead, with the colored lights shining forward | 3 NM | ||
| Over 65 ft | Sidelights must be separated | 2 NM | |
| Powered boat or sailboat using motor | Under 23 ft | Bi-colored combination light if available | 2 NM |
| Under 165 ft | Must show separated sidelights | 2 NM |
In the table below is a selection of the sidelights offered by Apex Lighting.
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Example of Sidelights in a Sentence
"The system of red on the left and green on the right found in boat sidelights can also be found on buoys."
Synonyms: port and starboard lights, combination lights
Related Terms for Sidelights