[SML] Moving Light Colour Mixing philosophy question

[Mick Alderson]

Andrew Riter asked:

> I like Jerry's point of white source = all colours / RGB = spiky RBG versions of a colour, so subtractive is better colour.  But subtractive is also less intensity in the saturated colours.
> 
> The question is more:  why are subtractive systems  CYM and not RGB?

The Additive system works by adding combining light frequencies to trigger the same color receptors in your eye that a single discrete frequency band would. Since the eye’s receptors perceive (overlapping) bands of Red, Green and Blue, you can trick the brain into seeing colors that aren’t actually there just using RGB. You are building towards “white" from a relatively few colors. Since LEDs emit very narrow bands of color, you get a spiky actual spectrum.

Fixtures using the CYM subtractive system start out with white light and filtering out the colors you don’t want. Your eye sees what is left. CYM filters will each pass 2/3’s of the spectrum and block only 1/3. Any combination of two will at least pass the 1/3 they have in common. What is left is still a range of what was a fairly full spectrum and not so spiky. But RGB filters each pass only 1/3 of the spectrum and will block the other 2/3’s. Any two will together block the entire spectrum.

Mick Alderson
Stagehand
IATSE Local 470