sidelight

noun

1. A light found at the side of something; especially of a vehicle.“If it starts getting misty, put your sidelights on.”
2. A light found at the side of something; especially of a vehicle.; (nautical) Red and green navigation lights indicating each side of a ship for collision avoidance; red on the port (left) and green on the starboard.
3. A window found at one or both sides of a door.
4. A piece of incidental information that helps one understand a subject.“A book of this type is necessarily mainly factual, but it is diversified by many incidents and sidelights which help to give life to a story now accorded its due place in railway history.”