CTO (colour temperature orange) is an orange correction filter used to lower a source’s correlated colour temperature. It is commonly used to warm daylight-type light toward a tungsten appearance, or to make a smaller intentional adjustment.
Choosing a strength
Full, half, quarter and eighth CTO are common descriptions, but use the specific manufacturer’s data. The starting spectrum and CCT affect the result. Fractional strengths are not simple fractions of a fixed kelvin change.
A specific example
LEE 204 Full C.T. Orange is specified to convert 6500 K daylight to approximately 3200 K. That is a product-specific conversion, not a promise that every “full CTO” takes every source to exactly 3200 K.
Using CTO on set
For a tungsten-balanced interior with daylight entering through a window, CTO may help warm the daylight contribution. Meter or test the result with the camera, allow for light loss and follow the material’s heat and mounting guidance. CTO changes the light; changing camera white balance changes how all the light in the shot is interpreted.
Related terms
CTB (Colour Temperature Blue) · CCT (Correlated Colour Temperature) · Diffusion