Formation light

A formation light was a source of illumination mounted on the exterior hull of a starship or other spaceship, similar to a running light.

On a starship, formation lights were situated on the dorsal surface of the primary hull, either side of the impulse engine, and on the underside of the secondary hull beneath the shuttle bay. 

Formation lights were mounted in several positions on starships, such as the aft secondary hull, dorsal and ventral surfaces at the rear of the warp nacelles, and the starboard and portside rim of the primary hull.