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:

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:

diagram of boat navigation light positioning

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.


NaviLED PRO LED Navigation Lights

NaviLED Pro Bi-Color

NaviLED PRO Bi-Color Navigation Light

Deck Mount LED

Deck Mount LED Navigation Lamp Kit

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