Physics Notes: Visible spectrum-colour 4. Primary and secondary colours
Visible spectrum and colour: 4. What do we mean by primary colours and secondary colours? - red, green, blue and cyan, magenta, yellow - Venn diagrams for mixing colours
Doc Brown's Physics exam study revision notes
4. Primary and secondary colours
(refer to the Venn colour diagram)
Why are some colours designated as primary? What are secondary colours?
In this section, imagine you are shining lights onto an object or a screen, including mixing beams of light of different colours.
Although it is possible to mix two colours to make a different colour (e.g. yellow = green + red) it has not been found possible to produce either red, green or blue by mixing other colours.
Therefore red, green and blue are referred to as the primary colours. When these three are mixed together you make white light.
Yellow, cyan and magenta are referred to as secondary colours, because they can be created by mixing two of the primary colours.
yellow = red + green
cyan = green + blue
magenta = red + blue
By mixing a primary colour and a secondary colour you can reproduce white light.
red + cyan = white, green + magenta = white, blue + yellow = white
You can demonstrate all these effects with a suitable projector, screen and coloured light filters (but only certain types of filter work effectively).
Colour sources e.g mineral pigments or organic molecules can be mixed together to make a wide variety of colours.
Cautionary note with reference to the visible spectrum diagram above:
Keywords, phrases and learning objectives for visible light and primary and secondary colours
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