Additive Primary Colours

Additive colour

Red Green and Blue light combined, produce white light.

Additive colours are colours that are associated with emitted light directly from a source before an object reflects the light. These colours are red, green and blue. These are the colours we are probably most familiar with in association with television, and computer displays. The additive colour theory, was first described by James Clark Maxwell in the mid 1800s. When equal amounts of Red Green and Blue light are combined, they produce white light. By adding the colours together to produce white, we call these additive colours.

Red, green and blue are the "primary" colours of white light. The combination of all three of these colours will result in white. This is called Colour by addition and is direct way to prove that all of these three colours do indeed come from white light.

Understanding additive colours

Additive colour

The three colour torches above show how when red green and blue are mixed, other colours are produced... including white!
This is called colour by addition.

A simple way to understand a little more about additive colours is to create some of your own using torches or 'flashlights' with coloured filters attached.

The three colour torches show how when red green and blue are mixed, other colours are produced... including white! This is called colour by addition.

You will need:

Three similar torches (preferably identical ) Light filters or similar to cover the torch heads elastic bands (to hold the colour filters in place) A white surface to shine your torches

Step 1.

Cover the front of each torch with a colour filter - one torch with a Blue light filter one with a Green light filter, and the other with a Red light filter. Use the elastic bands to hold them in place.

Step 2.

Arrange the torches so that the beams of light just overlap each other on the white surface. You may need to enroll a friend to help you do this! You could also use three photographic tripods if you access to them... and tape the torches to them.

For the best results, use a white wall or surface to shine the torches on. The effect is also best achieved in a dark room.

Step 3.

If you have the torches arranged correctly, the result is that in the middle of the three light beams, the area is white. It may take a while to arranged the torches correctly, but once they are, you should see that in the middle where all three colours meet the are is white.

You will also see other colours that have been produced. These should be Magenta, Yellow, and Cyan (another bluish colour) These are called secondary colours.



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