the formula presented is the exact solution for any light-emitting disk with radius R >0 at any distance d >0. Of course there might be a very mild difference with a rectangular shopping window, and there might be a mild difference with a really ball-shaped lightbulb at very short range. I'm happy to create the specific formulas for them.

Any way it's a vast improvement over the generic 1/(a+bx+cx^2) aproximation with undertermined a,b,c presented elsewhere, and a vast improvement over the infinitely small physically non-existent point size lights.

In all cases, it shows constant lighting levels nearby which can be defined as say d< R, inverse square far-off behaviour which can be defined as say d > 3*R and a transition in the middle. So yes indeed, the falloff curve varies with distance from the source.

A shopping window at 10cm will be experienced as an infinite plane while the same window will be experienced as a point light when seen at 1000 mtrs. As a lightbulb at 1 mm from the bulb behaves like an infinite plane, and as a perfect point light at 10 mtrs. As a consequence, only the transition area R < d < 3*R will mildly depend on the shape of the light emitter. For Poser users this means: one function serves all, except for the extremes like long light strips.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though