In lighting theory, the ‘set light’ (aka background light) is the light used in a traditional lighting setup to illuminate the background or studio ‘set’ to give an audience a clearer picture of the location of the film composition as well as creating additional debt and separation from the subject or person in the foreground.

The concept of set light should not be confused with that of ‘working light’ which is simply like used on location to assist cast and crew in day-to-day activity on the set, working light is not used or seen in the final composition. In some circumstances working light may refer also to available light in a given filming location, for example daylight entering through a window.