# Optics: white object reflection properties

If a red light drops on a red object, we know that all of the red light is reflected, and none is absorbed. But what happens if a red light drops on a white surface, is all of the red light reflected, will the intensity of the reflected light be the same? Or will the reflected light be of a different spectrum(meaning different colour, since a very small portion is absorbed)?

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In both cases some light will be absorbed.
And the light reflected by the white surface will have the same wavelength as the incident light. Unless there is some fluorescence induced by the red light. (Not very likely for red light on paper)

How about the intensity? Will it be the same?

Drakkith
Staff Emeritus
How about the intensity? Will it be the same?
Probably not. It is very unlikely both surfaces would have the exact same reflectivity, but not impossible.

What Drakkith said.
But a "white surface" is not a mirror (is it?) and the reflected light will be diffuse. So the intensity (energy per unit area of angle) will be lower. But this is true (or may be) for the red surface too.

It may be that you are not asking the right question. Total energy reflected may be a better parameter. And this may be the same or not. Color is not the only factor.

If I had an device which would be sensitive to the amount and intensity of the light absorbed, would it show the same value(assuming the proposed variable is dependant on the factors mentioned before) for a red surface and a white one(not mirror)(presume a red light is falling to the incident plane, and the reflected the light is measured), assuming both of the surfaces are more or less the same(only the colour differs)? From your answers, I conclude that they would be the same, I just want to confirm this.

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How would you have a device sensitive to the light absorbed?
If it's absorbed, it's not there to be "sensed", is it?

I don't really understand your goal. What do you mean by "proposed variables"? What are these variables? And what is the "incident plane"?

Adding color to a white surface may change its reflectivity.
But you can also have two surfaces, one white and one red, with the same coefficient of reflection for you specific wavelength. What more is to it? The reflectivity of the surface depends on properties of the material as well as the wavelength of the incident radiation.