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). 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
surpising 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