Visible Light
Light, Sound and Waves

Mixing lights of different colours

Physics Narrative for 11-14 Supporting Physics Teaching

Combining colours

Combining three lamps covered with red, green and blue filters can make a whole range of colours.

red + blue  →  magenta (purplish-pink)

red + green  →  yellow

green + blue  →  cyan (turquoise)

If red, green and blue beams are directed onto a white screen, then where all three beams overlap a white patch is produced.

You cannot tell the difference between an appropriate mixture of these three beams and a spectral colour. So you can have an experience identical to that caused by any of the colours of the visible spectrum by mixing together combinations of red, green and blue light. For this reason, red, green and blue are referred to as the primary colours. The three colours produced by mixing two primary colours are called secondary colours.

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