In theater, running lights are any lights that the audience does not see, but are on during the run of the show. They are different from worklight

Worklight

In theater, a worklight is a high-intensity light fixture which is used to illuminate the stage for the benefit of technicians. Technicians use these lights rather than the stage lights for a number of reasons. Firstly, it take much less technical knowledge to turn on worklights, so even people...

s which are not used during a show. One type of running light is the lights set in wings or crossovers for actors and technicians to find their way in the (mostly) dark. These are usually rope lights or traditional fixtures with a colored lamp or colored gel

Color gel

A color gel or color filter , also known as lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction...

 over them. Booth staff will also use running lights to illuminate control boards or scripts. One brand marketed for this specific purpose is LittLite. Cue light

Cue light

A cue light is a system of one or more electric light bulbs used to allow silent cues to be given to technicians and performers at various working locations during the running of a show. Typically, the Deputy Stage Manager sends signals to these cue lights at pre-arranged times...

s are distinct from running lights.