Here's some info on "foot candles", I'm posting the excerpt just to make it easier but the link it came from (with more detailed information) is also posted at the bottom of this entry "Light":
Measuring horticultural light
Light for growing orchids is often expressed in terms of foot-candles of light. Foot-candles (abbreviated fc) simply measure the intensity of light, the amount that actually falls on a surface, or its illumination. A foot-candle is the density of an amount of light. Orchids are classified into three basic light groups: high (3,000+ fc), medium (2,000 to 3,000 fc), and low (1,200 to 2,000 fc). Foot-candles do not, however, measure the quality of light or its duration, and both are horticulturally important. But foot-candles do give a guide to the relative needs of different orchids, to help gauge certain categories of light requirements. Measuring light intensity by foot-candles is useful when assessing actual sunlight, which consists of the full range of the light spectrum, perfect for orchids. If you are growing orchids in sunlight, the quality of light does not have to be of much concern. The intensity of that sunlight is of interest, and it can be measured in foot-candles, using a photometer.
Another way to gauge relative intensity is with a hand/eye test. Put your hand between the light source and the plant, with the hand 6 inches above the leaves, and look at the shadow cast. A sharp-edged shadow means the light is high, a soft-edged shadow is probably good for medium- to low- light orchids, and no shadow cast means the light is not strong enough for an orchid to flower. Outside, in full sun on a bright summer day, the amount of foot-candles illuminating a surface is about 10,000. An overcast day yields about 1,000 foot-candles of light. The indoor light near a window can be as low as 100 foot-candles, or as much as 5,000 if the orchid is right up against the window on a clear day at noon at standard time on June 21, which is when the amount of light falling on the Northern Hemisphere is greatest. Measure light intensity on that date at noon to determine the maximum foot-candles that reach the orchids growing there.
Light.
I also wanted to learn more about footcandles. I have some info in my ortho's orchid book and they have that hand shadow test in there too. That's how i figure out where i should put my orchids.
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