The most common focusable unit used in the theatre today is the ellipsoidal (in theatrical slang, "leko"). The output of the leko is a round (conical), well-defined beam of light. Ellipsoidals come in a variety of beam spreads specified either by their actual beam spread in degrees, or by the lens diameter and the focal length of the lens. Because of the precise light control possible with the leko, these units, assuming the appropriate beam spread is chosen, are effective from any position in the theatre.

Stage lighting instrument. (2014, May 21). In Wikipedia, The Free Encyclopedia. Retrieved 12:21, July 26, 2014, from http://en.wikipedia.org/w/index.php?title=Stage_lighting_instrument&oldid=609507200