Foot candle calculation on desk surface
Hi All,
I am trying to understand foot candle calculations, in specific how to calculate foot candle on a work station if the light source (s) is/are located above the surface but positioned with an angle, like track lighting. Does the angle of the light source effect the foot candle amount on the surface? Based on my readings it does. However none of the books I read gives a formula for that situations. They all assume the light source being 90 degree perpendicular to the floor/horizontal works surface. Can anyone please help me on this or recommend a good source to understand foot candle calculations better? I am weak on this. Thanks!

Elif,
I was able to find that information in the Ballast ARE 5 review manual on page 3211. The formula is:
E = (I X cos θ) / d^{2}
 E is illumination measured in footcandles
 I is candlepower measured in candelas
 d is the distance from the source
 θ is the adjustment to account for the angle from vertical
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