Color gel

A color gel or color filter (Commonwealth spelling: colour gel or colour filter), also known as lighting gel or simply gel, is a transparent colored material that is used in theater, event production, photography, videography and cinematography to color light and for color correction. Modern gels are thin sheets of polycarbonate, polyester or other heat-resistant plastics, placed in front of a lighting fixture in the path of the beam.

Gels have a limited life, especially in saturated colors (lower light transmission) and shorter wavelength (blues). 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 filters are used. The main drawbacks are additional expense and a more limited selection.

In Shakespearean-era theater, red wine was used in a glass container as a light filter. In later days, colored water or silk was used to filter light in the theater. Later, a gelatin base became the material of choice. Gelatin gel was available at least until 1979. The name gel has continued to be used to the present day. Gelatin-based color media had no melting point, and the color was cast in the media as opposed to being coated on the surface. It would, however, char at high temperatures and become brittle once heated, so that it could not be handled once used in the lighting instrument.

By 1945, more heat-tolerant and self-extinguishing acetate-based through-dyed materials were being manufactured (marketed as Chromoid then Cinemoid by Strand Electric). In the U.S., Roscolene (acetate) was developed to deal with higher output light sources. Though cheaper, the acetate filters eventually fell out of favor with professional organizations since they 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 polycarbonates like Roscolar (mylar polycarbonate) and polyester-based filters. These materials have superior heat tolerance. Polyester having the highest melting point of 480 °F (249 °C).

Often a surface coating was applied on a transparent film. The first dyed polyester gels were introduced by Berkey Colortran in 1969 as Gelatran, the original deep-dyed polyester. The Gelatran process is still used today to produce GAMColor (100% of the line) and Roscolux (about 30% of the line). Other color manufacturers, such as Lee Filters and Apollo Design Technology, use a surface applied dye. (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. 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 prevent burn-through, and keep stage equipment and actors cooler.