Lighting
CTO / CTB Gels
01 — Definition
The filters that correct colour temperature. CTO (Colour Temperature Orange) warms a source — typically 5600 K daylight brought down towards 3200 K tungsten. CTB (Colour Temperature Blue) does the reverse, tungsten up towards daylight. They come in fractional strengths (1/8, 1/4, 1/2, full) to fine-tune the match. The downside: gel cuts output — a full CTB can cost over a stop of light.
02 — In the field
Match mixed sources by gelling the minority. To blend a few tungsten fixtures into a daylight-balanced room, put full CTB on the tungsten units: far fewer gels to cut and tape than gelling the whole daylight rig.