Objects on the other hand generally do not emit any light
but most objects selectively absorb incoming light. The analog
to the emission spectrum for objects is thus the absorption
spectrum which describes the percentage of incoming light of a
given wavelength that is absorbed by the object. Together with
the emission spectrum of a light source we can use the
absorption spectrum of the object to predict the wave length
distribution and corresponding intensity levels of light from
the source after it hit the object. Click here for an
example of such a process.
Despite all the applications and predictions of this theory
of colour, we still haven’t seen any fundamental reason why
light with a wavelength of 632nm appear read. For that
explanation we need to follow the light into the human
eye.
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