I have a little booklet that lists recommended footcandle levels for certain locations. For a Warehouse it is 20-50 Fc. As an example, a 400 watt metal halide lamp has a lumen output of 25,000. My question is: how can I convert lumens to footcandles? Am I comparing apples to oranges? Any help would be appreciated.

I think the formula is as follows: 1(one) lumen falling on 1(one) square foot of space is equal to 1(one) footcandle. Or lumens/sq. ft. = fc

Since you did not give the area that you want to light up, change the formula around to read: lumens /required fc = sq ft covered. or 25000/20 = 1250 sq. ft. You can see that if you want a higher fc rating the area will decrease. 25000/50 = 500 sq. ft.

There are alot of other items to consider, initial lumens, dust, height, angel of the light to the surface, etc..

I believe Philips has some information on this, check their web site at www.lighting.philips.com/nam

Rick Miell

Thanks for the information Rick. We have a "warehouse" application. 283ft. x 33ft. mounting height of 21ft. I'm considering installing (9) 400 watt metal halide high bay fixtures. That would give me 24 footcandles of light if my calculations are correct.

[This message has been edited by Frank Cinker (edited 03-01-2002).]

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

Scott,

Along with the information Rick provided I searched the internet and found the following web page. http://www.lightsearch.com/resources/lightguides/formulas.html

Zonal cavity calulations take into account reflectances, installation heights, etc. See link below: http://www.hubbell-ltg.com/download/technicalpdf/Zonal_Cavity_Calc.pdf

Frank,

I'll check out that link later today, then if time allows this weekend I'll post more to this thread.

Scott SET