Color gel

[1] Modern gels are thin sheets of polycarbonate, polyester or other heat-resistant plastics,[2] 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).

By 1945, more heat-tolerant and self-extinguishing acetate-based through-dyed materials were being manufactured (marketed as Chromoid then Cinemoid by Strand Electric).

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.

[4] Other color manufacturers, such as Lee Filters and Apollo Design Technology, use a surface applied dye.

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.

In the film industry, gels are usually cut straight from rolls 24 or 48 in (600 or 1,200 mm) wide and 50 ft (15 m) long, as the size required may vary from a single practical halogen spotlight in a ceiling to a whole window.

As the range demanded by designers increased and many more colors were offered in the 1970's and 1980's, two digits quickly proved inadequate.

Swatch books enable designers and technicians to have a true representation of the manufacturers' range of colors.

Most ranges of gels also include non-colored media, such as a variety of diffusion and directional "silk" materials to produce special lighting effects.

It is common for a gel manufacturer to publish the transmission coefficient or even the spectral transmittance curve in the swatch book and catalogs.