Color Gel

A color gel is a thin sheet of tinted plastic placed in front of a light source to change the color of the light. The name comes from early versions made of gelatin; modern gels are heat-resistant polyester. Photographers use them on flashes and studio lights to match mixed light sources or to add color for mood and style.

CTO stands for color temperature orange. It warms a light source, most often shifting a daylight-balanced flash toward the orange color of indoor bulbs at around 3,200K. Full CTO makes the shift completely, while half and quarter strengths apply smaller corrections. Photographers reach for CTO whenever flash has to blend with warm indoor lamps without looking cold and blue.

CTB stands for color temperature blue, the opposite of CTO. It cools a warm source toward daylight. A common use is placing CTB over a tungsten lamp so it matches window light or daylight-balanced flash in the same scene. CTB also comes in full, half, and quarter strengths, and it absorbs more light than CTO, so the lamp loses noticeable brightness.

For two reasons. Matching comes first: bare flash is daylight-balanced and looks cold next to warm room lamps, and no white balance setting can fix two colors of light at once. An orange gel makes the flash agree with the room. The second reason is creative: strong gels turn backgrounds, rim lights, and smoke into bold blocks of color.

Yes. Every gel absorbs some light, and deeper colors absorb more. A pale correction gel may cost a third of a stop, while a deep red or blue creative gel can cut two stops or more. The exposure has to come from somewhere, so photographers raise flash power, open the aperture, or push ISO to compensate.

Yes, with attention to heat. LED panels run cool, so a gel can sit directly on the front. Halogen and tungsten lamps get hot enough to warp or melt a gel, so the sheet needs a holder that keeps it away from the bulb. Purpose-made gels are heat resistant, but no plastic sheet survives direct contact with a hot lamp for long.

Small gels for speedlights come in kits and attach with tape, a rubber band, a velcro strap, or a magnetic holder. Studio strobes use clips, gel frames, or barn doors to hold larger sheets in front of the head. The attachment does not need to look tidy; it needs to cover the light source completely so no ungelled light leaks past.

Correction gels apply measured shifts in color temperature so mixed sources match: orange CTO, blue CTB, and green or magenta gels for fluorescent light. Creative gels are stronger colors chosen for style rather than accuracy, such as deep red, teal, or violet. The sheets work the same way; the difference is intent and strength.

Only partly. A global color shift can imitate a weak correction gel, but a real gel changes the light itself. A red gel on a background light colors only what its light reaches, with natural falloff and mixing where sources overlap. Recreating those local effects with masks is slow and rarely looks convincing, so lighting with gels first saves editing time.

They deal with fluorescent light. Older fluorescent tubes add a green cast, so a green gel, often called plus green, on the flash makes it match the tubes, and one white balance setting then cleans up the whole frame. Magenta, or minus green, does the reverse and removes a green cast from a source. Modern LED lights have made these corrections less common.