The Ellipsoidal Reflector Spotlight
The most commonly-used lighting instrument in the trade is the Ellipsoidal Reflector Spotlight, or ERS. The ERS is also commonly known as a Leko (pronounced "Lee-Ko"), named after its inventors, James Levy and Edward Kook. Leko is probably more widely-used than ERS, simply because it's easier to say, even though the name "Leko" is legally owned by a lighting company called Strand.

The ellipsoidal is named so because of its elliptical mirror (reflector) inside the instrument that bounces light from the source (lamp) out through the barrel (the long snooty part of the instrument). The barrel contains a two adjustable glass lenses that change the beam of light that the instrument emits. An electrician can "run the barrel" to change the focus of the beam to a hard or soft edge, depending on the effect that the light designer wishes to give. Lekos are also equipped with four shutters that can cut the circular beam to any quadrilateral shape.

An ERS is usually identified by its dimensions, which is a combination of the diameter and focal length of its lenses. For instance, a 6x9 (six by nine) ERS has lenses that are 6" across and a 9" focal length. The longer the barrel, the longer the focal length, and the thinner and sharper the beam that the instrument emits. This is because the longer focal length creates a smaller "beam angle" and thus a smaller area of light. The wider the lenses, the longer the instrument's "throw distance," the longest distance from the focal area that the instrument can effectively illuminate to.

The ellipsoidal pictured above is from Electronic Theatre Controls' elite Source 4 series. Source 4 ellipsoidals feature rotatable barrels as well as brighter, energy conserving lamps. A source 4's 575-watt lamp casts as much light as a regular ERS of 1,000 watts. Source 4's also have cold mirror reflectors that absorb much of the heat from the source, making the instrument cooler and easier to work with while lit up. Altman also has its own Source 4-type series called "Shakespeare." Shakespeare instruments possess most of the same special features as the Source 4.

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