a prism is a triangular piece of glass that refracts white light into its separate coloured components
The colour of bright sunlight seems to be yellow/white but that is somewhat an
illusion. In fact white light consists of a combination of rays with different wavelengths
in the visible part of the spectrum. In 1665 it was Isaac Newton who noticed that
images he made with his self fabricated lenses became vague at the edges and were
surrounded with a small area of light in different coloured bands. After a long period
of experimenting he finally concluded that the phenomenon was not caused by
imperfections in the lenses itself but that the cause was to be found in refraction of
the light. This refraction occurs when a bundle of light passes two substances with
different propagation characteristics, for instance air and water or air and glass. In air
the propagation speed of light is higher than it is in water or in glass. This causes the
light to bend more ore less, depending on the angle at which the light falls unto the
water or glass. Since the degree of bending is slightly
different for the several colour components of white light,
such a bundle of light will be refracted in separate
colours. In science and industry it is often a prism that is
used to refract light. A prism is a triangular piece of glass
that, due to its triangular shape, bends the light twice and
refracts it into its separate components. In a prism the
unexpected side effect of Isaac Newton his lenses is
optimised and revalued into wanted behaviour.
Principally the combination of an equal amount of all colours of light, would result in a
pure white light but in relation to sunlight the situation is a little more complicated
since the presence of the colours green and yellow is relatively high. Besides that,
the human eye is relatively sensitive for the colour yellow but whether or not this is
caused by the composition of the sunlight is not completely clear. The final result
however, is that we notice the sunlight with a touch of yellow. When the sun is
located near the horizon, the atmosphere will cause an additional filtering of the
sunlight making its colour seem to be more reddish.