Ellipsoidal is the name for a type of theatrical light, getting the name from the ellipsoidal reflector used to intensify the light of a back-loading lamp through the barrel and lens. Ellipsoidals are used for their strong, well-defined light and their versatility.

Characteristics of an ellipsoidal lighting unit include:

• An adjustable barrel, allowing a lighting designer to change the size and focus of the light thrown by the unit by changing the distance between the mirror and the lens or lenses
• A set of brackets on the end of the barrel for the insertion of gel frames to change the color of the light
• A series of shutters at the base of the barrel for shaping and narrowing the light beam
• A slot in the body of the unit for the insertion of metal gobos to change the pattern of the light

The most popular type of ellipsoidal light in modern theaters is the Source Four as they combines all the best features of an Ellipsoidal while being fairly inexpensive and easy to use.