An interior light bar adapted to be installed on the rear deck of a vehicle for projecting light out of the rear window. The light bar has a pair of projection units each having a housing and each slidably mounted on a rail which extends through the housings from an end thereof and along a rear, closed side. The units each contain light emitters which project the light out of the open side of the units. The units are assembled with a selected separation distance so that the ends through which the rail extends are essentially in contact or sufficiently spread apart to clear a brake light assembly on the rear deck or even further apart so as to provide a wide width of illumination out of the rear window from the light bar. The rail may be channel which provides a conduit for wiring from the light emitter units. Fasteners which connect the housings and the rail into an integrated assembly extend through the closed side of the housing. These fasteners may also connect to a slotted L bracket for providing height and lateral adjustability of the light bar toward and away from the window upon installation of the deck.