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Spectral Color vs Temperature
Name: Christopher
Status: student
Age: 12
Location: N/A
Country: N/A
Date: 2001-2002
Question:
Do the different colors of the spectrum have different
temperatures?
Replies:
Any object at temperatures above absolute zero emits radiation. Let us
concentrate on an ideal "black body." This ignores the complexities
associated with real bodies and surfaces.
The radiation emitted by a black body (or a real body) is not at a single
color (wavelength). At a given temperature an object emits a broad range of
radiation according to an equation known as Plank's Law, after Max Plank,
the German scientist that discovered it.
Conversely, there is a range of temperatures at which a body emits a
significant amount radiation at a particular color (wavelength). However, a
body at a particular temperature gives off the largest fraction of its
radiation at a particular wavelength (color). It is in this sense that one
can say that different colors (wavelengths) have different temperatures.
Ali Khounsary, Ph.D.
Advanced Photon Source
Argonne National Laboratory
Christopher,
The colors do not have specific temperatures, they have frequencies. A
frequency is how fast something vibrates. A light waves vibrates as it
travels, rather like a wave traveling along water. Different colors
correspond to different vibration frequencies. A hotter object can produce
a more quickly vibrating light wave, and blue light has a higher frequency
than red light. As a result, a blue flame is hotter than a red flame.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
I aguessing a bit about what your question means. Electromagnetic
radiation, of which visible light is a small part, can generate heat if it
is absorbed by some object, and this may increase the temperature. So in
that sense light can be said to generate heat, but that is not usually meant
to indicate that the light "has a temperature".
The more common way in which light and temperature are related is what is
called "black body radiation". This is the radiation that you see when you
turn on
an electric stove and the burner glows red, but this is actually a
continuous spectrum of light extending into the infrared. As the object is
heated to a higher temperature this distribution of light wavelengths
changes decreasing in the average wavelength, but still a continuous
distribution of wavelengths. What your eyes perceive is that the "color"
becomes more orange then yellow then bluer, and finally it becomes "white
hot" when the temperature is so high that all wavelengths in the visible
range 400 to about 700 nanometers have about equal intensity.
In photography, and other applications, you will sometimes see what is
called a color temperature. What this term means is the temperature you
would have to heat a "black body" to in order that the radiating object has
the perceived color.
Vince Calder
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