What is a Lighting Gel?

A lighting gel (often just called a gel or filter) is a thin, heat-resistant coloured filter placed in front of a stage light to change its colour, correct its colour temperature or soften the beam. Gels are used on conventional fixtures such as PARs, profiles and fresnels.

How lighting gels work

Using gels involves a few simple steps:

  1. Choose: the lighting designer picks a colour from a manufacturer's swatch book, where each gel has a number.
  2. Cut: the gel is cut from a sheet or roll to fit the fixture's frame.
  3. Fit: it slides into a gel frame at the front of the light during the focus.
  4. Replace: gels fade and burn over time from the heat, so they are checked and replaced regularly.

Gel colours are listed on the light plot so the crew can fit the right ones during the load-in. Venues often keep their colour lists with the technical specification, shared as documents in Crescat.

Lighting gels vs LED colour mixing

Gels give a conventional light one fixed colour. LED fixtures mix colours electronically and can change colour on any cue, with no gels needed. Many rigs still use gels on conventional lights for rich, consistent colours, especially in theatre.

Main types of lighting gel

  • Colour gels: change the colour of the light, from pale tints to deep saturates
  • CTO (colour temperature orange): warms light to match tungsten or sunset tones
  • CTB (colour temperature blue): cools light to match daylight
  • Diffusion or frost: softens the beam and blurs its edges
  • Neutral density: reduces brightness without changing colour

Frequently asked questions

What do gel numbers mean?

Each manufacturer gives its colours a number, so designers can specify an exact shade. Lee Filters and Rosco are the best-known makers, and many designers write the brand and number on the plot, such as "L201".

Why do gels fade or burn?

Stage lights run very hot, and the heat slowly bleaches the dye in the gel. Deep blues and other saturated colours fade fastest and may need replacing after a few shows.

Are lighting gels still used with LED lights?

Mostly not for colour, because LEDs mix their own. Diffusion gels are still used on LEDs to soften the beam, and gels remain common on conventional theatre lights.

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