Additive and subtractive synthesis of colours
Age Group
12 13 14 15 16 17 18
Expected time
3 periods
Guess the colour.PDF
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Guess the colour!

What’s the mystery? The colour of the objects around us depends on the surface of the object, on the colour of the light that illuminates them, and the system of human perception. If many small pieces of differently coloured cardboard are placed under a nearly monochromatic light, it can become very difficult to distinguish the colours.
Domain(s) Physics
Subdomain keywords Additive and subtractive synthesis of colours.
Age group 12 to 18 years old.
Expected time for the mystery Approximate time for teacher preparation: two hours.Approximate time in classroom: three or four individual 50-min lessons.
Safety/supervision Laser pointers have to be handled with care and never directed towards people’s eyes.Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials Green and red laser pointers, diffraction gratings, coloured and white cardboards, green LED light, blue LED light, red LED light, coloured filters, black blankets, supports to be covered by the blankets (so that each group will not be disturbed by the lights being used by the other groups).
Learning objectives
  • To become familiar with the additive synthesis of lights and with the subtractive synthesis of the coloured pigments.
  • To become familiar with how colours look under different coloured lights.
Resources The first video is a 1950s educational documentary about colour:

The following video pertains to the additive synthesis of light and the physiology of vision. In addition, it briefly discusses the fact that there is no correspondence between a colour and a wavelength: