Cyc lights (thus named because they are effective for lighting the cyclorama, a curtain at the back of the stage), also called border lights, have long housings typically containing multiple lamps arranged along the length of the instrument and emitting light perpendicular to its length. Lamps are often covered with gels of multiple colors (often red, green, and blue, which, in theory, allow almost any color to be mixed) with each color controlled by a separate electrical dimmer circuit.