Color gel
Encyclopedia
A color gel or color filter (UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 spelling: colour gel or colour filter), also known as lighting gel or simply gel, is a transparent colored material that is used in theatre
Theatre
Theatre is a collaborative form of fine art that uses live performers to present the experience of a real or imagined event before a live audience in a specific place. The performers may communicate this experience to the audience through combinations of gesture, speech, song, music or dance...

, event production, photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...

, videography
Videography
Videography refers to the process of capturing moving images on electronic media even streaming media). The term includes methods of video production and post-production...

 and cinematography
Cinematography
Cinematography is the making of lighting and camera choices when recording photographic images for cinema. It is closely related to the art of still photography...

 to color light and for color correction
Color correction
Color correction by using color gels, or filters, is a process used in stage lighting, photography, television, cinematography and other disciplines, the intention of which is to alter the overall color of the light; typically the light color is measured on a scale known as color temperature, as...

. Modern gels are thin sheets of polycarbonate
Polycarbonate
PolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...

 or polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...

, placed in front of a lighting fixture in the path of the beam.

Gels have a limited life, especially in saturated
Saturation (color theory)
In colorimetry and color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color...

 colors. The color will fade or even melt, depending upon the energy absorption of the color, and the sheet will have to be replaced. In permanent installations and some theatrical uses, colored glass filters or dichroic filter
Dichroic filter
A dichroic filter, thin-film filter, or interference filter is a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characterized by the color of light that they...

s are being used. The main drawbacks are additional expense and a more limited selection.

History

In Shakesperean theatre, red wine was used in a glass container as a light filter. In later days, colored water or silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

 was used to filter light in the theater. Later, a gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...

 base became the material of choice. Gelatin gel was available at least until 1975. The name gel has continued to be used to the present day. More heat-tolerant self-extinguishing acetate-based materials (marketed as Cinemoid and Roscolene) were developed to deal with higher output light sources. This material fell out of favor, since it could not withstand the higher temperatures produced by the tungsten halogen lamps that came into widespread use in the late 1960s. The acetate-based material was replaced by polyester and polycarbonate based gels. Those materials have superior heat tolerance when compared to acetate-based gels. Polyester "gels" were introduced in 1969 as Gelatran, the original deep dyed polyester. The Gelatran process is still used today to create GAMColor. Other color manufacturers, such as Lee Filters
Lee Filters
Lee Filters is a Hampshire-based UK brand of colour filters and colour gels for the lighting and camera industry. Their colour gels for stage lighting are the industry standard in Europe while competing with other brands such as Rosco....

 and Apollo Design Technology use polyester as their color substrate. Lee and Apollo use the surface dyed process. Roscolux is 70% polycarbonate and 30% deep dyed polyester. Almost every color manufacturer today uses either polycarbonate or polyester to manufacture their "gels". Even today's gels can burn out (to lighten in color starting in the center) easily, rendering them useless. To help combat this, a high temperature (HT) material (polyester having the highest melting point 480 °F (250 °C)), can be used to help prolong the life in high-heat output lighting instruments. As instrument design improves, it has become a selling point on many lights to have as little heat radiating from the front of the fixture as possible to help prevent burn-through, and help keep the stage and actors cooler during performances.

In the theater, gels are typically available in single 20×24-inch (500×600 mm) sheets, which are then cut down to the appropriate size before use. The size originates from the gelatin days: it is the same as a standard baker's sheet, which was used to cast the sheets. In the film industry, gels are usually cut straight from rolls 24" or 48" (600 mm or 1200 mm) wide and 50' (16 m) long, as the size required may vary from a couple of inches to gel a Dedolight or a practical halogen spotlight in a ceiling to many feet to gel a whole window, so a standard sized sheet would be impractical.

Colors

Similar colors may vary between different companies' formulations - for example, many have a color named "bastard
Bastard (color)
In theatre lighting, a bastard color refers to a color, typically in a color gel, wherein the predominant color is blended with small amounts of complementary colors; for example, a "bastard orange" gel would produce predominantly orange light with undertones of blue. Bastard colors appear warmer,...

 amber", but the transmitted color spectrum may be different. For this reason, gel colors are not referred to by name. Using nature’s color spectrum as a guide, Apollo Design Technology uses a four digit number to designate and locate specific color transmissions: Visible Spectrum. Some manufacturers use a code consisting of a letter and number combination. For example, G841 is a dark blue made by Great American Market (GAM), and R02 is a light amber made by Rosco and L216 is a diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 filter made by Lee Filters
Lee Filters
Lee Filters is a Hampshire-based UK brand of colour filters and colour gels for the lighting and camera industry. Their colour gels for stage lighting are the industry standard in Europe while competing with other brands such as Rosco....

.

Manufacturers produce swatch books, which contain a small piece of each color available, adjacent to its color code, to simplify ordering. Swatch books enable designer
Designer
A designer is a person who designs. More formally, a designer is an agent that "specifies the structural properties of a design object". In practice, anyone who creates tangible or intangible objects, such as consumer products, processes, laws, games and graphics, is referred to as a...

s and technician
Technician
A technician is a worker in a field of technology who is proficient in the relevant skills and techniques, with a relatively practical understanding of the theoretical principles. Experienced technicians in a specific tool domain typically have intermediate understanding of theory and expert...

s to have a true representation of the manufacturers' range of color.

Most designers choose a limited color palette for generic applications because it is financially and logistically difficult to have access to all colors for a single show.

There are also gels for color correction
Color correction
Color correction by using color gels, or filters, is a process used in stage lighting, photography, television, cinematography and other disciplines, the intention of which is to alter the overall color of the light; typically the light color is measured on a scale known as color temperature, as...

, such as CTB and CTO, "Color Temperature Blue", and "Color Temperature Orange" respectively. Color correction gels alter or "correct" the color temperature
Color temperature
Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of...

 of a light to more closely match the color temperature of a film negative or the white balance of a digital imager. Specifically CTB, which is blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...

 in appearance, will correct tungsten lights that typically have a color temperature in the range of 3,200 kelvins to 5,700 kelvins to more closely match the color temperature of "Daylight" negative, which is usually around 5,400 kelvins (nominal daylight). CTO, which is orange in appearance, will correct a "Daylight" balanced light source (such as many common HMI
Hydrargyrum medium-arc iodide
Hydrargyrum medium-arc iodide, or HMI, is a Osram brand metal-halide gas discharge medium arc-length lamp manufactured for the film and entertainment industry. Hydrargyrum is Latin for mercury...

 bulbs) to match the color temperature of Tungsten negative, which is typically 3,200 kelvins. There are "half" and "quarter" variations of the common color correction gels. It is common to use color correction gels for artistic purposes and not just for negative-to-lightsource correction.

Most ranges of gels also include non-colored media, such as a variety of diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 and directional "silk" materials to produce special lighting effects. "Opal" for example is an opalescent
Opalescence
Opalescence is a type of dichroism seen in highly dispersed systems with little opacity. The material appears yellowish-red in transmitted light and blue in the scattered light perpendicular to the transmitted light. The phenomenon is named after the appearance of opals.There are different degrees...

 or translucent diffusion filter
Diffusion filter
A diffusion filter is a translucent photographic filter used for a special effect. When used in front of the camera lens, a diffusion filter softens subjects and generates a dreamy haze. This can also be improvised by smearing petroleum jelly on a UV filter or shooting through a nylon stocking...

.

It is common for a gel manufacturer to publish the transmission coefficient
Transmission coefficient
The transmission coefficient is used in physics and electrical engineering when wave propagation in a medium containing discontinuities is considered...

 or even the spectral transmittance
Transmittance
In optics and spectroscopy, transmittance is the fraction of incident light at a specified wavelength that passes through a sample. A related term is absorptance, or absorption factor, which is the fraction of radiation absorbed by a sample at a specified wavelength...

 curve in the swatch book and catalogs. A low transmittance gel will produce relatively little light on stage, but will cast a much more vivid color than a high transmission gel, because the colorfulness of a light source is directly related to narrowness of its spectral linewidth
Spectral linewidth
The spectral linewidth characterizes the width of a spectral line, such as in the electromagnetic emission spectrum of an atom, or the frequency spectrum of an acoustic or electronic system...

. Conversely, the flatter its curve becomes, the closer the gel is to a neutral density filter
Neutral density filter
In photography and optics, a neutral density filter or ND filter can be a colorless or grey filter. An ideal neutral density filter reduces and/or modifies intensity of all wavelengths or colors of light equally, giving no changes in hue of color rendition.The purpose of standard photographic...

.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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