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I read that a (sufficiently) white surface reflects more (visible) light than a mirror. Is that true? And if yes, why?

Raffael
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2 Answers2

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Have you ever wondered why things show colour? Well when light is incident on a surface, light of certain wavelengths are absorbed and we see the complement colours.For example a green surface absorbs light of all colours other than green. But a white surface is a surface that reflects out light of all wavelengths unlike a black surface which absorbs all light.

Now imagine shining a green laser at a mirror . What we get is a reflected green beam.if we repeat this experiment for all other 6 colours we will get similar results.So we can conclude that a mirror reflects light of all colours just like a white surface .

So what makes a mirror different from a white surface?

A mirror possesses specularity i.e parallel rays are reflected parallel to each other thus maintaining an image which does not happen for all white surfaces. A surface which is not a mirror does not reflect the parallel rays in a specular fashion so the reflected rays mix into one homogeneous white light without producing image.

So basically if I take a white surface and give it the property of specularity I get a mirror.

Typically how much light is reflected depends on the surface.For example if you take a sufficiently white surface it will reflect 100 % light but if you compare it with a household mirror that reflects only 80% light then the white surface would reflect more than the mirror.

Möbius
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What we refer to as "white" is actually a large collection of colors. (I'm not talking about "off-white", I'm talking about all the shades we call "white".)

For example, there are hundreds of "white" paints, but they all have different Light Reflectance Values up to 98.1%.

Likewise, there are a lot of different types of surfaces that we call "mirrors".

A household metallic mirror will reflect up to 95% of light. However, dielectric mirrors can reflect up to 99.999% of light.

There isn't really a well-defined lower bound on how much light must be reflected to be considered "white" or "a mirror", but at the upper bound, mirrors are capable of reflecting more light than white paint.

A "sufficiently" white surface could theoretically reflect 100% of light, but I'm not sure anything like that exists in nature or has ever been created.

cowlinator
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