Why does a room illuminated by a television appear blue?
Color television pictures are produced by three different colors: red,
green and blue. These combine to create a whitish light with a color
temperature close to that of daylight (5500 to 6500 Kelvin).
Color temperature is a way of describing the relative amounts of the
different colous that make up the light from a particular source. It
can be thought of roughly as the temperature an object would need to
be heated to give off light with that mixture of wavelengths. At low
temperatures, low-energy colors such as red and yellow predominate; at
higher temperatures the proportions of green or blue increase.
For example, standard tungsten light bulbs have a color temperature of
3200 K and are very yellow. Your eyes adjust to this light, making it
appear whiter and more like daylight. At twilight or at night,
anything with a higher color temperature than tungsten lights, such as
a television, appears distinctly blue.
The same effect is seen if you look out of a room lit by tungsten
light. The twilight appears particularly blue, and yet if you were to
go outside and look at the same scene, the eye would no longer compare
it to the lit room and the colors would appear more neutral.
The converse is also true. Viewed from outside, the windows of houses
lit by tungsten light sources look distinctly yellow. Fluorescent
sources generally have a spectrum much closer to that of daylight and
don't produce the same effect.
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