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A lamppost will give the most light directly under the lamp. The illumination will decrease when you move away from the light source. This relation is shown by a curve, which I give the name illumination curve. When the lamp gives light homogenous in all directions, the light stream for each unit
of area is inversely proportional with r2. For a sloping bundle of light the
light stream is proportional with the cosine of the angle α.
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