If you thought colour mixing with lights would be simple due to your expert knowledge from being a child stood at your easel, apron smothered whilst making an excellent shade of purple with your paint... then you’re wrong. Lighting is a whole new kettle of fish, so let’s start with the basics.
Addative colour mixing
First of all the primary colours in lighting aren’t the same as the primary colours in painting. In lighting you are working with Red, Green and Blue (RGB). With these three colours you can then mix to create your other colours. This style of lighting is referred to as additive colour mixing.
By changing the intensity of an individual colour you can create a wide range of colours, in fact, with a DMX controller you can create over a million slightly different shades. By adding all the colours together to an equal amount you can create white.
Whilst that seems very simple in reality, it doesn’t work quite as well. With RGB lighting the colours may not mix quite as well, this has been improved as the quality of LEDs improves. The white tends to be very blue and because of the way the colours are added it’s hard to create pastel colours with RGB lighting.
To solve this problem some manufacturers have started adding a white or amber LED to create RGBW or RGBA lights. These create a nicer white as you have a pure white light that you can add to the colours. By adding tints of other colours such as red or blue you are able to create nicer pastel colours. The addition of the white LED makes LED lighting more accessible for theatre use. When using the white LED and a red tint you can start to create a more tungsten output that the human eye preserves as nicer colour on skin. This is something that’s very hard to achieve using RGB lighting.
Subtractive colour mixing
This is where we move to secondary colours which are Cyan, Magenta and Yellow (CMY). So if you were to mix the Blue in your fixture with the Green you would produce Cyan, if you were to mix Blue with Red you would produce Magenta and if you were to mix Green with Red you would get Yellow. These colours are used for subtractive lighting. This process is quite often found in moving heads where rather than starting with a colour and adding more colours to create white, you start with white and remove colours until you get to black.
For example, in a moving head you would have a lamp outputting a ‘white’ colour. A disk with ether Magenta, Cyan or Yellow is placed in front of the lamp to give it a colour. So the further the Magenta wheel moves infront of the lamp the less of the other colours it lets through. As the Magenta wheel lets the blue and red light waves through you can then add yellow or cyan to create the colour you require. (See diagram below). By Adding all three colours together you get black/no output from the lamp.