Page 8 - Understanding light, colour and hair colour
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The human eye can only see wavelengths between 400 nanometers and 700 White light travels until it hits an object where it is absorbed by that
nanometers violet through to red. Why is that? White light enters the pupil object, the pigments that determine the colour of that object reflect the
and passes through a transparent lens without pigments, just like the prism it corresponding wavelengths, telling the human eye the colour of that
refracts individual wavelengths to the back of the eye; the wavelengths are object.
absorbed by the Retina which lines the back of the eye. The Retina contains
two different types of cells known as cones and rods. Proof of this can be clearly seen when four sheets of card of four
different colours white, red, green and blue are hit by the same white
Cone cells accept the wavelengths red, blue and green also the wavelengths light source, only the area where the light hits reflects the pigments with
nearest to them. It is the ability of the cone cells to accept red, blue and the relevant wavelengths telling the Retina cone cells the colour reflected.
green wavelengths and mix them that makes it possible for the human eye
to recognise over 300 different colours. The area outside the beam of white light can only be seen as dark grey or
black by the rod cells of the Retina. (Please see Fig. 7)
The rod cells do not recognise any wavelengths from the visible spectrum Fig. 7
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)
The above different colour card experiment helps us understand that all
wavelengths are absorbed and only the corresponding wavelengths to the
pigments in an object are reflected, this is the same for everything touched
by white light; from a tree to a human hair. Also, this experiment answers
Fig. 6 how we view colour in the dark at night and in the daylight.
(Please see Fig. 8)
