Color gel

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A color gel or color filter (UK colour gel or colour filter), or a lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to colour light and for color correction. Modern gels are thin sheets of polycarbonate or polyester, placed in front of a lighting fixture in the path of the beam.

Gels have a limited life, especially in saturated 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 filters are being used. The main drawbacks are additional expense and a more limited selection.

[edit] History

In early days coloured water or silk was used to colour light in the theatre. Later, gelatin became the material of choice. More heat-tolerant self-extinguishing acetate-based materials (marketed as Geltran, Cinemoid and Roscolene) were developed to deal with higher output light sources. This material fell out of favour, since it could not withstand the higher temperatures produced by the tungsten halogen lamps that came into widespread use in the late 1960s. The name gel however has continued to be used to the present day.

Gels are typically available in single 20×24-inch (500×600mm) sheets cut from rolls 24" or 48" (600mm or 1200mm) wide and 50' (16m) long, 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.

[edit] Colors

Similar colors may vary between different companies' formulations - for example, many have a color named "bastard amber", but the transmitted color spectrum may be different. For this reason, gel colors are not referred to by name, but instead by 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.

Manufacturers produce swatch books, which contain a small piece of each color available, adjacent to its color code, to simplify ordering. Swatch books enable designers and technicians to have a true representation of the manufacturers' range of color.

There are also gels for color correction, such as CTB and CTO, which alter or correct the color temperature to be higher with a light blue, or lower with a light orange, respectively. A "half" CTB or CTO is very light, for minor corrections.

"ND" is a neutral-density grey, meaning it affects all colors evenly and brings the light down by a given number of f stops.

Most ranges of gels also include non-colored media, such as a variety of diffusion and directional "silk" materials to produce special lighting effects. "Opal" for example is an opalescent or translucent diffusion filter.