Hair Light: Light source aimed at a subject`s hair to create separation from the background and add sparkle and highlights.

Halation: The distortion that appears around the edge of a sharply focused beam pattern. This effect can be reduced with the aid of a donut.

Half Scrim: A metal scrim whose screen occupies one half of its frame so that the straight edge of the screen is located across the diameter of the frame. It is used to cut light output.

Halogen: The name for a family of gases, used in lamps, to maintain proper color temperature.

Hard Edge: A beam pattern edge that is very clear and distinguishable, i.e., one without a fuzzy or blurry perimeter.

Hard Light: Illumination that has a hard edge and produces sharply defined shadows. Often this light is very intense, but generally less flattering than soft light. A light source that provides such illumination.

Head: A general term for a Fresnel spotlight. The part of a follow spot that contains the light source, i.e., not the stand, ballast or interconnect cable. The part of a metal halide light source that contains the lamp, i.e., not the ballast or interconnect cable. The part of an ellipsoidal spotlight that contains the reflector, i.e., not the lens barrel or the cap. Short for Grip Head or Ball Head.

Hertz: A unit of measurement for the Frequency of alternating current, i.e., one cycle per second.

Highboy (Hiboy): A heavy-duty stand designed to hold light sources or heavy grip equipment. The stand is equipped with wheels and tall risers, and usually a 1 and 1/8" receiver and a grip head.

High Key: A lighting style in which the majority of the scene is highly illuminated, usually enhanced by bright costumes and sets. A low ratio of key plus fill light lowers the contrast, helping to obtain this effect.

Hollywood Box: A piece of power distribution equipment used in the film and video industries, composed of a metal housing, a means for connecting an electrical supply and female flush-mount connectors or bus bars that can be electrically connected with bus bar lugs, for the purpose of supplying electricity to light sources. Some are also provided with over current protection.

Hot Lights: Common term for continuous light sources, especially tungsten or halogen lights that run hot.

Hot Restrike: A term applied to an igniter that can hot-start an arc lamp.

Hot Spot: The spot of light with the highest intensity, ideally located at or near the center of a beam that has been focused for a peak field.

Hot Start: A term used to describe the ignition of a heated arc lamp, i.e. a lamp that has just been electrified.

HMI: Abbreviation for Hydrargyrum (Greek for Mercury) Medium-Arc Lodides. This is a commonly used type of metal halide lamp manufactured by Osram-Sylvania Corp. The term Osram HMI is trademarked.

Hz: Abbreviation for Hertz.

Illumination: Generally, a term for light or lighting. In photometry, the amount of light, i.e., luminous flux per unit area incident on a surface, in foot-candles or lux.

Incandescent: A term used to describe a lamp, or a light source that utilizes such a lamp, that employs the incandescence of a filament as its light source. The filament is housed in a vacuum enough electricity is passed through the filament that it glows. Such a lamp was first developed by Thomas Edison (United States) and Joseph Swan (Great Britain), independently, in 1879.

Indirect Lighting: Illumination that falls on an area or subject by reflection, e.g. bounce lighting.

Inky: A small Fresnel spotlight with a 1.5" to 3" lens diameter, usually 100250 watts.

Intensity (Light Output): The strength of the incident light source, independent of the subject`s reflectivity.

Inverse Square Law: The quantity of light is inversely proportional to the square of its distance, i.e., illumination (fc) = Intensity (cd) / Distance2 (ft2). Say a light is placed 1 foot away from the subject. If the distance is doubled to two feet, the square of its distance is (22) or 2 x 2 = 4. The inverse of 4 is 1/4. Therefore, the quantity of light falling on the subject from 2 feet will be 1/4 the amount of light falling on the subject from the original 1 foot. If the light is moved to a distance of 8 feet, the square of its distance is (82) or 8 x 8 = 64. The inverse of 64 is 1/64. The quantity of light on the subject from 8 feet will be 1/64 the amount of light that falls on the subject from 1 foot away. Each time you roughly increase the distance incrementally, you open up your aperture two, three, four stops, etc., to compensate for the light falloff.

Iodide: A halogen gas used in lamps to maintain proper color temperature.

Iris: Short for Iris Diaphragm.

Iris Diaphragm: An arrangement of thin movable heat-resistant metal plates, i.e. leaves, that form an adjustable circular opening. They are usually placed within an ellipsoidal spotlight or follow spot in order to adjust the diameter of the beam, or in some cases, to mechanically dim the beam.

K: Abbreviation for Kelvin. Short for Kilowatt in the theatre, film and video industries.

Kelvin (K): In the metric system, a graduated scale used to measure temperature with 0° (-273° C) being the total absence of heat (absolute zero). Each degree is the same magnitude as a degree in the centigrade scale. The Kelvin scale is used to gauge color temperature.

Key Light (Main Light): The principle source of light, which establishes the character of the lighting, including atmosphere and mood. It may suggest a source, like the sun, or a window.

Key Grip: The supervising grip on a production, the person ultimately responsible for all other grips and grip equipment.

Kicker: A sideline, low angle back light that adds a slight edge light to the side of the subject.

Kilowatt (kW): 1000 watts.

Lamp: Any light source in a self-contained package composed of an envelope (containing gas, filaments, etc.), filament or electrodes, base, contacts, gas and any support structures. The source can be of the incandescent, fluorescent, quartz halogen, LED or arc type. Quite often this term is used interchangeably with light source.

Lamp Base: The part of a lamp to which the electrical connections are made the part with the contacts. It is often the mechanical support or heat sink for the lamp.

Lavender: A type of material used for fabric scrims.

Leads: The electric cable(s) or sleeved, insulated wires, attached to a light source or piece of power distribution equipment, that terminate in a connector for the purpose of providing an electrical connection to the electrical supply or to another light source.

LED: Otherwise known as Light Emitting Diode.LED lights give off light and little-to-no heat (making them safer fixtures as well) and are more environmentally friendly than standard lighting fixtures.

Leko: A commonly used term for an ellipsoidal spotlight. Named after its inventors Joseph Levy and Edward Kook, the names Leko and Lekolite are trademarked by Strand Lighting Corporation.

Lens: A transparent material, usually glass, shaped to bend light rays as they pass through it. Colored lenses can also be used as color media.

Light: Illumination the aspect of radiant energy of which a human observer is aware through a visual sense. Its electromagnetic radiation has a wavelength longer than ultraviolet radiation but shorter than infrared radiation, i.e., approximately 380mm (violet) to 750mm (red). A term that is often used interchangeably with light source.

Light Distribution: The way in which illumination of any color or quantity is spread over a particular background.

Lighting Ratio: The percentage of key light to fill light. Optimum and maximum lighting ratios depend upon subject matter, mood, media and type of reproduction, as well as personal tastes. In television a timid ratio is 2:1 (twice as much key as fill), a dramatic one, 8:1 (eight times as much key as fill, popular for film-noir look) a maximum one, about 16:1. Also called Brightness Ratio.

Light Meter: An apparatus used to measure various quantities of light such as color temperature, foot-candles, lux, flash, etc.

Light Source: Anything that emits light, such as an arc or a filament, a lamp or light head, bulb or flash.

Light Spill: A general term used to describe any stray light, including light leaks.

Location Fresnel: A Fresnel spotlight used primarily in non-standard production settings such as locations other than stages or studios. Because portability is generally a concern, they tend to be smaller in size when compared to studio Fresnel`s of the same wattage.

Long Throw: A term used to describe a light source that has an effective intensity at a relatively long distance. This term is very subjective and dependent on the type of light source used.

Louver: An opening provided with one or more slanted fixed or movable fins to control the angle of light, like venetian blinds for lighting.

Lowboy (Loboy): A heavy-duty stand designed to hold light sources or heavy grip equipment. The stand is equipped with wheels and short risers, and a 1 and 1/8" receiver and a grip head.

Low Key: A lighting style in which the majority of the scene is scarcely illuminated, usually enhanced by shadows and dark costumes and sets. A high ratio of key light to fill light increases the contrast, helping to obtain this effect.

Lumen(s): A unit of measurement for Luminous Flux, a measure of the total amount of visible light emitted by a source. A measure of brightness most commonly used when referring to video projectors. Brighter projectors are required for larger screens or in rooms with natural light.

Luminous Flux: The rate of flow of light energy evaluated, in Lumens, with reference to visual sensation the part of the total energy radiated per unit time from a luminous source that is capable of producing the sensation of sight.

Lux: A metric unit of measurement for Illumination, e.g. 1 lumen per square meter.