MadSci Network: Physics Query:

### Re: Why isn't violet cooler than red since it reflect more energy?

Date: Thu Dec 5 09:46:32 2002
Posted By: Jeff Robertson, Associate Professor of Astrophysics
Area of science: Physics
ID: 1038771321.Ph
Message:
```
Colors other than Black or White are tricky.
Black absorbs all wavelengths of light and will be warmer
than White (totally reflective).
However, colors are usually a mixture of pigments, each
absorbing bands of different wavelengths.  For example,
sky blue is a combination of blue and yellow wavelengths being
reflected, others absorbed.  So to say that a violet color
ONLY reflects violet is not true, nor is a red color
ONLY reflecting red.

Have you ever been to the paint store to watch them color match
a paint color.  White paint goes in along with
a squirt of red, a squirt of yellow, a squirt of blue
and wow Periwinkle paint!

The moral is that the color you see may be a combination
of many different wavelengths.
For practice you can visit these interactive color wheels
to produce colors from the three standard colors (RGB). http://www.exploratori
um.edu/exhibits/mix_n_match/

There are two ways to look at light.  You can imagine light as a wave or as a
stream of particles called photons.  In answering this question, it is best to
think of light as a stream of particles.  We can say that violet light is of a
higher energy than red light because each photon in violet light contains more
energy than a photon in red light.

If you went to a shop and a man offered you a tonne of silver or an ounce of
gold for the same price, you would take the silver.  Gold may be far more
valuable than silver, but the quantity of it is so much less in this case that
it makes sense to take more of the lower value metal.

The violet object is not emitting anywhere near the same number of photons as
the red object.  So, even
though the photons from the violet object have a higher energy, the amount of
radiant energy being given  off from this object is less than the red one.  The
violet object therefore gives off less radiant energy and in so doing, becomes
hotter than the red object.

It is true that your objects will be giving photons of different colours, but
in the case of red, we can say for instance that a large proportion of the
photons emitted will be in the red part of the spectrum. Therefore, I feel that
the above reasoning has validity.

Richard Kingsley

```

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