Color vision Our eyes are actually fairly poor color detectors. We cannot
distinguish all the different wavelengths that are revealed by a diffraction
grating. In fact, all we can do is determine the brightness of the
light in three broad color ranges -- a range of long wavelengths (reds),
a middle range (greens), and short wavelengths (blues).
A representation of the sensitivity of the three color detectors in the
eye. Note that the regions overlap; this means that light of a single
wavelength (pure yellow, for example) will be detected as red+green.
The
result is that there can be lights with very different spectra that to
your eyes are indistinguishable -- just as there are many recipes for your
favorite soup. In this respect the eye is like a tone-deaf person, who
can only sing three notes - and the only music that person can make is
the result of combining only those three notes. Color photography
and color television are only possible because the eye has this rather
limited ability to distinguish between the different wavelengths. A physically
accurate representation would need a thousand different wavelengths, instead
of just three; we would need a thousand different little color dots on
the computer screen, all so close together that they seemed to be at the
same place! This distinction between the color the eye can perceive
and the physicist's definition in terms of the different frequencies of
light becomes important when we try to predict what will happen if we mix
different colors of paint, or if we try to match the color of two objects
and want the match to remain true for all kinds of lighting.
An important result of the eye's limited ability to detect individual
color occurs when we mix colored light. We perceive a mixture of
all colors of light as white light. Combine red, green, and blue
light and we see not red, not blue, not green - but white!
(One way to do this is described in the
last page of this section).
Even more surprising to
many people is the idea that if we combine red and green light, the result
is yellow. Within the spectrum made by a diffraction grating there
is also a region that looks yellow, but now this is not a mixture of anything
-- light having this wavelength is "pure yellow." Our eyes and brain
interpret the mixture of red and green in exactly the same way that they
see pure yellow.
Colors of objects
