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Q & A: Is there color without light?

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Most recent answer: 01/08/2012
I was told that the way our eyes perceive color is based on how the light reflects off that object. So, I was wondering, do objects still have color when there is no light? For example, if I were to turn off my bedroom light, would my walls still be blue, like they are when the lights are on?
- Rebecca (age 13)
Columbia, KY, USA
That's an interesting question. The answer partly depends on what you mean by "color".

Of course if there's no light around, there's no color that you can see. On the other hand, the wall must have some property that makes it be blue. That property is still there in the dark.

So I guess in a way what the question amounts to is to ask if there's anything you could measure about the wall that says it's blue without having to actually put light on it. The answer to that is yes. For example, a chemical analysis of the paint could show that it contains pigments that would mainly reflect blue light. You could even rig the analyzer to report that to you by sound only.

For formalists, the fluctuation-dissipation theorem says that the absorption spectrum of the wall, together with the temperature, uniquely determines the spectrum of the electromagnetic fluctuations on it. Actually, for light at room temperature the temperature is unimportant. The spectrum of the quantum mechanical fluctuations in the electromagnetic field, present even without light, determine what the absorption spectrum will be.

Mike W.

(published on 01/08/2012)

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