Source and Reflected Color
When I shone a blue tinted daylight bulb into a
light blue object, it appeared white. Is it possible to use
certain light filters to make objects appear colorless or white,
or is it a trick of the eye? if so, how does this work?
It is not a trick of the eye in the usual sense. The "color" your eye
sees is composed of the wavelengths of light absorbed or reflected by
the object. In addition, the amount of light of a certain wavelength
depends upon the wavelengths that the light source produces. It is the
combination of these two effects (plus the eye's sensitivity to
different wavelengths of visible light) that results in the "color"
one perceives. Technically, this effect is called "metamerism". You
have to keep in mind that the color of an object appears under
reflected light by the complementary wavelength that is absorbed by
the object. So for example, an object appears "yellow" because the
object removes "blue" from the wavelength that is incident upon the
object. In any particular case the perceived color becomes a rather
complex response to the wavelengths absorbed and/or reflected.
It is a trick of the eye. Since the light incident on the object is
enhanced in the blue, it is reflected fairly evenly throughout its
frequency range by the light blue object. Your eye interprets this to be
a white object, because that is what white objects do.
Your eye makes this compensation because we see things in light of
varying compositions: the red of sunset, the blue of shadows, the yellow
of daylight, and the orange of firelight. At sunset, a zebra does not
turn red, so our eyes and brain do the best they can to relate what they
see to what is probably there. In the case of the pale blue object in
bluish light, it does not work. But you really cannot do any better than
that; in pale blue light, a white object reflects pale blue light, so
the pale blue object looks just like a white one!
Department of Physics and Astronomy
University of Wyoming
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Update: June 2012