Frank,
Try applying Photometric data to the desired Fc.
Foot-Candle Power would be the "Designing Level" [the light level that is desired] to shoot for.
The Lumens would be a figure of Light Output from a specific Luminare [Fixture and Lamp type].
Lumens per Watt would be the Efficiency Factors to consider when figuring the type of Luminare to be used.
Color Redention is another factor.
Apply these figures to Photometric Plots for various Luminares - in order to find a good design level of Fc.
The Photometrics will cover Fc at various levels.
Don't forget to include "Lumen Maintenence" factors with these calcs! This would include the Lumens available after lamps have been in service for a few Months.
These correction factors range from 20% to 40% reduction of output Lumens, as applied to certain lamps and fixtures. The Manufacturer[s] can supply this data, or you could figure a constant value yourself.
Rick has covered the basic calcs, along with other information very well!!
Scott SET
