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Newton proved the human eye can only see wavelengths between 400
      nanometers and 700 nanometers violet through to red.  Why is that?  White

      light enters the pupil and passes through a transparent lens without

      pigments, just like the prism it reflects individual wavelengths to the back of
      the eye; the wavelengths are absorbed by the Retina which lines the back of

      the eye. The Retina contains two different types of cells known as cones and


      Cone cells accept the wavelengths red, blue and green also the wavelengths

      nearest to them.  It is the ability of the cone cells to accept red, blue and
      green wavelengths and mix them that makes it possible for the human eye

      to recognise over 300 different colours.

      The rod cells do not recognise any wavelengths from the visible spectrum
      so it is these cells that recognise brightly coloured objects in the dark as just

      solid dark grey or black shapes. (Please see Fig. 6)

        Fig. 6
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