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Name: Clarence L.
Status: N/A
Age: 16
Location: N/A
Country: N/A
Date: 7/13/2004


Question:
If the color black absorbs more light than the color white, then why is it that you can see your reflection better on a black billiard ball than a white billiard ball?


Replies:
Many objects have a combination of specular (mirror-like) reflection from the very surface, and diffuse reflection (flat color) from particles under the surface. Gloss white is exactly that. You can imagine white powder embedded in clear casting resin; that is the model for your white billiard ball.

Gloss black is simpler. It only has the specular reflection. The internal diffuse reflections can be suppressed to a great degree, something achieved by few other reflections in optics.

The specular reflection off the surface of glass or plastic is about 4-5% of the incident light. You have only 1/20 of a good mirror there. The faint image is easily drowned out in glare from any source. White powder behind it can reflect 90% of the light as diffuse white. This is many times stronger than the image, and your eye's discrimination of relative brightness has limits. You can see a sharp change of something like 3% in light intensity, but less than that gets difficult.

Also much easier to see your reflection in a window of your house when it is dark outside than when it is daylight outside. Even if there are no distinct features to see outside, only hazy sky. This is pretty much the same issue as black vs white billiard balls.

Jim Swenson


There are two processes going on. The "black" vs. "white" is a bulk property of the billiard balls. The reflection is a surface property. The "black" billiard ball shows your reflection better because no light is reflected back from the ball proper. The same effect occurs in a black shiny car vs. a white shiny car.

Vince Calder


An interesting question...

There are two sources of light that you are seeing. There is the light that is reflected from the surface of the ball and there is the light that is not absorbed by the material in the ball (the absorption occurs very near the surface). The amount that is reflected at the surface has a lot to do with how the surface is prepared / polished. This is essentially the same for both the white and the black balls.

The amount that is not absorbed by the material depends on the material the ball is made of. Much more light is not absorbed by the white ball.

The image you see in the reflection is formed from the surface reflection. The not absorbed light is scattered so that it doesn't form an image. As a result, both balls have about the same amount of light in the image but the white ball has much more light that isn't part of the image. This additional, non-image, light interferes with the quality of the image.

This is similar to looking at a reflection in a partially silvered mirror. If the room behind the mirror is dark the image is easily seen. If the room behind the image is bright it is difficult to see the reflected image.

Greg Bradburn



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