Page 8 - Understanding light, colour and hair colour

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

refracts 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. (Please see Fig. 6)

Fig. 6