Stage lighting instrument
Stage lighting instruments are used in stage lighting to illuminate theatrical productions, concerts, and other performances taking place in live performance venues. They are also used to light television studios and sound stages.
Many stagecraft terms vary between the United States and the United Kingdom. In the United States, lighting fixtures are often called "instruments" or "units". In the UK, they are called "lanterns" or "luminaires". This article mainly uses terms common to the United States.
Components
Stage lighting instruments all have the following components:Housing
The lamp housing is a metal or plastic container that serves as a body for the entire instrument and prevents light from spilling in unwanted directions. It comprises all of the exterior of the fixture except for the lens or opening. The housing may be designed with specific elements that help reduce heat and increase the efficiency of a lamp. Older instruments were made from rolled and machined steel or aluminum. With the advent of the Source Four, many lighting instruments are being made from die cast metal. Die casting allows for one single, light-weight body that is more economical to produce and use. The first lantern to make use of die castings was the Strand Pattern 23 designed by Fred Bentham in 1953, this small mirror spot enjoyed a 30-year production run and found its way into many British schools, halls and theaters. Some instruments are made from plastic, such as the Selecon Pacific.Lens or opening
The opening is the gap in the housing from where the beam of light is intended to come. Many fixtures use a lens to help control the beam of light, though some, such as border or cyclorama lights, do not have any lenses or optics other than the reflector. The lens and the reflector, along with other beam-altering devices, are both considered part of the optics system.There are two main lens types. Profile Lens Systems and Wash Lens Systems. Instruments with profile lens systems usually have a beam that is narrow and hard edged. ERS lights and follow spots use these lenses. On the other hand, fixtures such as PAR's and Fresnels use wash lens systems. The wash lens system casts a diffused wash of light with a softer beam edge.
Reflector
The reflector affects the quality and directionality of the light output. A reflector is located behind or around the light source in such a way as to direct more light towards the lens or opening. Each unit has a characteristic reflector, used in conjunction with the lens to create the desired effect. An ellipsoidal reflector has a lamp set at one focus point of an ellipsoid-shaped reflector that bounces the light and focuses it at the second focus point of the ellipse. This focuses the beam of light into a tight beam. Ellipsoidal reflectors often are used for tight, focusable spots, although they can be used for floodlights, such as in scoops. A parabolic reflector has a lamp set at the focus point of a parabola-shaped reflector that bounces the light in parallel beams away from the reflector. There is no point at which the light converges, so the light is unfocusable. Parabolic reflectors are used for lights intended to provide an unfocused wash, such as PAR cans.Reflectors can also be used to selectively reduce or eliminate unwanted thermal emission. Incandescent lamps produce light through heating of the filament, while arc lamps produce light through the heating and ionization of a gas. In either case, this heat is also emitted from the lamp as infrared light. The thermal energy is often projected onto the stage with the visible light, and thousands of watts of incandescent lighting can be uncomfortably hot for the actors on stage. Specially designed reflectors are able to absorb and dissipate infrared at the fixture before the visible light reaches the stage.
Yoke
Most instruments are suspended or supported by a U-shaped yoke, fixed at two points to the sides of the instrument, providing an axis of rotation. The base of the yoke is typically a single bolt around which the yoke can be rotated, providing a second axis of rotation. Combined, these two axis allow the fixture to point nearly anywhere in a spherical range of motion encircling the yoke.The yoke is connected to a pipe or batten by one of the clamps mentioned below. It may also be affixed to the deck with floor mounts, or attached to the set with a stage screw.
Some yokes are motorized, allowing remote control systems to change where a fixture is pointing during a show.
Attachment apparatus
are hook clamps that use a threaded bolt to attach to a pipe or batten and to hold the instrument secure. Once secured, the fixture can be panned and tilted using adjustment knobs on the yoke and clamp. In addition, safety cables are used to support the lighting instrument in case the clamp fails.A side arm is a metal pole bolted to the instrument with a clamp on the end. This enables the instrument to be hung to the side of an electric as opposed to below it.
Lamp or arc source
All instruments need some type of source to produce light. The bulbs used are referred to as lamps. Stage lighting instruments typically use incandescent lamps, tungsten-halogen lamps, encapsulated arcs, or LEDs. Most theatrical lamps are tungsten-halogen, an improvement on the original incandescent design that used halogen gas instead of an inert gas. Fluorescent lights are rarely used other than as work lights. Although they are far more efficient, they cannot be dimmed without using specialized dimmers, cannot dim to very low levels, do not produce light from a single point or easily concentrated area, and have a warm-up period during which they emit no light or do so intermittently. High-intensity discharge lamps are now common where a very bright light output is required, for example in large follow spots, HMI floods, and modern automated fixtures. Because these types of lamps cannot be electrically dimmed, dimming is done by mechanical dousers or shutters that physically block portions of the lamp to decrease output. Some specially designed fittings now use light-emitting diodes as a light source. LEDs are ideal where an intense but unfocused light source is required, such as for lighting a cyclorama. LEDs have now been added to fixtures such as the Source Four LED, which looks similar to the source four onstage, but is controlled with LEDs.Incandescent lamps are most likely the type of light one is used to seeing. They are typical household lights that are usually between 40 and 100 watts. However, the US has been taking them out of production due to their inefficient nature. Typically, an incandescent lamp has a tungsten filament surrounded by an inert gas. This is all encapsulated by a bulb. The inert gas stops the formation of anything that could darken the bulb, such as carbon. The bulb is usually made from Pyrex or synthetic quartz. Incandescent lamps also have a base. The base screws into a socket and serves as an electrical contact point for the socket and the filament inside. For the most part, higher watt bulbs will use larger bases. Incandescent bulbs for stage lighting may have pins on the bottom instead of a screw. This allows them to be positioned properly in relation to a reflector. The filament of the lamp is usually tightly coiled tungsten wire.
Tungsten-Halogen lamps, or T-H lamps, are similar to incandescent bulbs, but instead of an inert gas being used, a halogen gas is used. Halogens are chemically active. Therefore, when the filament releases tungsten particles, the halogen gas forms a compound with them that the filament attracts back. The particles of tungsten then attach to the filament again. Because of this, there are less tungsten deposits on the bulb and the filament is constantly rebuilt, and so the light lasts much longer than a typical incandescent light.
LEDs are of an advantage because they are available in many colors today. LEDs are semiconducting diodes that emit light. The chemical composition of the LED determines the color of the light. Unlike conventional fixtures, LEDs do not need dimmers, but have intensities controlled by wattage. LED lights are much more energy efficient than incandescent or T-H lamps. While a household incandescent may be rated for 100 watts, an LED of the same intensity could be under 15 watts. One of their advantages to T-H and incandescent bulbs is that they do not require colored gels. LED fixtures typically come with multiple colors of LED lights. Color theory shows that mixing the primary colors of light will make white light. Therefore, through color mixing, LED's can form a wide variety of colors from white light to deep primary colors to many others. This reduces the time taken to change the color of an already hung fixture. The introduction of the LED allows much more variety of color and they also require much less power, making them useful to have in a theater or production.
Arc sources produce an electric arc. Electric current moving in the gap between the two electrodes creates a bright blue light. They are typically found in follow spots and moving fixtures. One of their downsides is that they cannot be dimmed: the light can be on or off. However, mechanical dimmers such as dousers, with slats or an iris to limit the light leaving the fixture, can be used to control the amount of light leaving the fixture.