An Ellipsoidal reflector spotlight or Profile Spotlight (abbreviated to Ellipsiodal or ERS) is a light with a strong, well defined beam, and is very versatile. Leko and Source Four are two of the most common brand names of these lights.
Commonly the light includes:
- A gel holder
- A gobo holder
- Several shutters to shape the beam.
- 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 smooth, plano-convex lens or lenses
There are several advantages of the ERS that make it one of the most common lights in a theatre. Its Ellipsoidal lens means only a 500w or 750w bulb is needed, instead of a 1000w bulb, while retaining the same brightness. Some ERSes, notably the Source Four, also include a dichroic reflector, so the beam is much cooler than other lights. Dichroic reflectors only reflect light from the visible spectrum, allowing infrared (heat) radiation to pass out the back of the light. This prolongs the life of gels and gobos.
Ellipsoidals can have either a fixed field angle, normally from 5° to 50°, or a variable field angle, commonly called a "Zoom". ETC, who manufacture the Source 4, produce a variety of attachments, commonly called "barrels", to change the field angle of the Source 4.
Ellipsoidals can be used for colour washes, with an attachment to change the field angle, but this job is better suited to PAR cans, Fresnels and Floodlights. Ellipsoidals are good for gobo projection, and highlighting actors or scenery on stage. They can also be used to god-spot actors by placing them at a sharp (5° - 10°) angle. This gives the effect of divine intervention, or, if used with a green gel, alien abduction.