Ellipsoidal reflector spotlight (abbreviated to ERS, or colloquially 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 may also be referred to as Profile Spotlights (especially in Europe). Ellipsoidals are used for their strong, well-defined light and their versatility. Leko and Source Four are brand names which may occasionally be used to refer to any sort of ellipsoidal. 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 smooth, plano-convex lens or lenses
- A set of brackets on the end of the barrel for the insertion of gel frames or a colour changer unit to alter the colour 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
- A further slot for the addition of an iris to narrow the beam whilst keeping its circular nature.
The ERS improves over the efficiency of the fresnel lantern by surrounding the lamp in an ellipsoidal reflector, as opposed to the spherical reflector of the fresnel. This results in a much more controllable beam of light, which is typically shaped inside the instrument, through the use of shutters, as opposed to externally, using barn doors. The biggest advantage of the ERS is its lower power consumption; the cost savings in electricity offset the higher initial cost of the instrument. 750 or 575 watt lamps are typically used, rather than the 1000 watt lamps common in older models. ERSes generally provide better illumination and produce a cooler beam of light than older lamps, as they include dichroic reflectors and so reflect only the visible portions of the spectrum. The lamps are loaded from the rear, and either mounted axially, or radially with the base either up or down (the orientation is important when mounting the instrument as using the light upside down will shorten lamp life) at a 45-degree angle. The filament of the lamp is at one focus of the ellipsoidal reflector and the aperture to the lens housing at the other. The shutters and gobo are ideally in focal point of this aperture.
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Field Angle
Ellipsoidals are supplied with a certain size lens that determines the field angle, normally five to fifty degrees. Field angle is the angle of the beam of light where it reaches 10% of the intensity of the center of the beam. Most manufacturers now use field angle to indicate the spread that the fixture has. However older fixtures are described by the width of the lens x focal length of the instrument. For example, a 6x9 ellipsoidal would have a 6" lens and a focal length of 9". This nomenclature was used because traditionally, the larger the lens, the more light output, however this is no longer true so most manufacturers now identify their fixtures by beam angle and light output. 6x9 Instruments have a field angle of approximately 37°. 6x12 instruments have a field angle of approximately 26°. As the field angle narrows, the instrument can be used further from the stage. Variable focus instruments with two lenses are also available, allowing the user to manually adjust to the desired focal length.[1]
Re-Invention
In 1992, lighting control manufacturer Electronic Theatre Controls (ETC), introduced their first attempt at stage lighting instruments. The effort proved extremely successful, as the fixture possessed some innovative new features. It used a standard lamp, had excellent optics, and used much less power than other instruments to produce the same luminous output. The Source Four lighting instrument inspired other manufacturers to build lights with similar designs. ETC has since introduced a complete line of stage lighting products with the Source Four namesake. They are the most commonly used lights in theatre today.
Similar lights
Products similar to the Source Four ERS include the Altman Shakespeare, the Strand SL and the Selecon Pacific. The Selecon Pacific has an irregular shape, which is because it is designed to reflect light off of a dichroic cold mirror, which has a heat sink to draw heat out of the instrument. This improves shutter, gobo and color gel life, and also can improve the temperature on stage.[2]
References
- ^ Gillette, J. Michael (2003). Designing With Light: An Introduction to Stage Lighting, Fourth Edition". McGraw Hill, 60. ISBN 0-7674-2733-5.
- ^ Gillette, J. Michael (November 10 2004). Theatrical Design and Production: An Introduction to Scene Design and Construction, Lighting, Sound, Costume, and Makeup. McGraw Hill, 365. ISBN 0-07-256262-5.
