MadSci Network: Physics

Re: Why is one shadow darker than another shadow?

Date: Thu Jan 13 10:15:01 2000
Posted By: John Link, MadSci Admin
Area of science: Physics
ID: 947311037.Ph

It is probably a matter of CONTRAST. Our eyes are not very good at measuring absolute light levels, but they are better at determining the difference in the amount of light of nearby areas. So, what looks like a darker shadow for the object closer to the light might actually be the same "darkness" but it looks darker because the surrounding area is brighter.

Try to borrow a photometer or a camera light meter and measure the absolute light level of both the shadows and the area surrounding the shadows and see if the contrast problem explains your observation.

John Link, MadSci Physicist

[Another possibility is that indirect light is lightening the one shadow more than the other. Let's assume that the same white screen is used to observe both shadows. The object nearer the light source makes a bigger shadow on the screen than the farther object does. A bigger shadow would then imply that less light reflects or scatters back from the screen. Less reflected light from the screen then implies there is less twice-reflected light lightening the shadow on the screen. This argument assumes that there is something in front of the screen to reflect or scatter light back at the screen. This something could be the walls of the room where the experiment is done or even the backside of the object that creates the shadow, especially if it is lightly-colored.

Everett Rubel ]

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