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What is LAW OF INVERSE SQUARES?
Suppose a candle is placed at #A with a screen at #B at a distance of two feet.
The screen shown is bent to represent part of a spherical surface with a candle at center.
Light passing through an open area #abcd will fall on area #a'b'c'd' on a screen in position #C four feet from the candle.
Since similar dimensions of the two areas are proportional to distances of the screens from the candle, area #a'b'c'd' is four times the area #abcd; hence since the number of rays of light to both surfaces is the same, the illumination on #a'b'c'd' is only one fourth that on #abcd.
Doubling the distance from screen from the candle reduced the illumination to one-fourth its former value.
From these and similar reasoning may be deduced the law of inverse squares: The illumination, or flux of light per unit area, produced on an object by a source of light so small as to be essentially a point varies inversely as the square of distance of the object from the source.
references for this page: LAW OF INVERSE SQUARES, LIS, LOIS
reference to this page: FOOTCANDLE