[Leica] Underexposure in Tungsten Light

[abridge at gmail.com (Adam Bridge)]

Another factor about tungsten light souces is that they more correctly
treated as point sources even when relatively close to them so light
intensity falls off inversely proportional to distance squared.

But flourescent fixtures typically look like planar sources or line
sources which, if you're relatively close to them (and if I'm
remembering my rad-con rules of thumb appropriately) fall off just
inversely proportional to distance. (Assuming the ceiling is
reasonably low).

This would account for tungsten sources giving you a hard time because
light fall-off across an image would be more severe.

I've not looked at the spectrum of most incandescent bulbs but for
most vendors you can find those graphs on the net and compare them to
the published response graphs of the film you use.

I'd never thought about light in quite these terms before. D'oh!

Adam