Page 10 - HAIR COLOUR

So, Newton has proved that the human eye can only see wavelengths
between 400 nanometres and 700 nanometres 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 rods.

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. (Fig 7.)

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