Color Gel

The color gel—in English color gel or simply gel—is a heat-resistant, translucent plastic film that is stretched in front of light heads to specifically alter the color temperature or hue of the light. Lee Filters and Rosco are the two dominant manufacturers; their color catalogs with four-digit numbers (Lee 201 = Full CTB, Rosco 3407 = CTO) are essential equipment for any lighting crew. A gaffer without gels is like a painter without a palette—the film is the primary tool for coloring, correcting, or dimming light.

CTO, CTB, and Plus Green: The Daily Standards

The three most important gel types regulate color temperature: CTO (Color Temperature Orange) converts daylight (5600K) to tungsten light (3200K)—Full CTO (Lee 204) absorbs about two stops of light, Half CTO (Lee 205) one. CTB (Color Temperature Blue) does the opposite—tungsten to daylight—and Full CTB (Lee 201) eats up a full two stops. Plus Green (Lee 244) adds green components to match HMIs to old fluorescent ceiling lights on office sets. Quarter, Half, and Full are the gradations; the gaffer intuitively reaches for the correct strength once they assess the mixed lighting situation on set.

Diffusion Filters and Effect Gels

In addition to color correction gels, there are pure diffusion filters: Opal (Lee 250, minimal light loss) for slight diffusion, 216 (Lee 216, approx. 1.5 stops) for soft, even light, and Grid Cloth for strong diffusion with moderate loss. Effect gels in red, green, magenta, or deep blue ("Party Gels") are used for music videos, club scenes, or deliberate stylizations. An experienced gaffer often combines multiple gels in a gel frame: for example, Half CTO plus Quarter Plus Green to perfectly match a fluorescent ceiling to a daylight window.

Practical Pitfalls and Lifespan

Color gels age under heat: CTO and CTB on powerful Fresnels (5kW and above) fade—after four hours of continuous operation, Full CTB can already become Half CTB. Therefore, the lighting crew checks the gels during longer breaks and replaces them preventively. Folds and creases in the gel create uneven color patches on the wall—the gel is not ironed; it is cut anew. A standard sheet of Lee film costs about 6–8 Euros and measures 1.2 × 0.6 meters; this is enough for two normal-sized Fresnel frames. In the low-budget realm, gels are often attached to barn doors with clothespins—this works as long as the pins don't melt.