Calculating lumens or fc using zonal lumen summary or RCR

[JeffBabineaux]

Our customer is requiring 40 fc for their indoor lighting. They've given us a layout for light fixtures, but the only description they've given us for what fixture to use is to make sure that the fixture provides the required fc at 3' working height at this fixture spacing. Can I use the tables I have here for our lighting fixture photometrics to calculate this? I've found previous threads that recommend Visual 2012, but 1- I don't think our IT wants to spend more money for another program that 2- might not be necessary given the information from our vendors. Thanks in advance!


On my first attempt, I found an angle from fixture to working height of 26 degrees, and used the 0-30 degree values from the zonal lumen summary to find lumens per square foot. This value, however, is at around half of what they're looking for, while the 12 light fixtures for 533 ft² seems a bit overkill.

 

[ron]

Use the RCR and CU in a zonal cavity calculation.

If they are spread out evenly, the angle from a fixture to the working surface is irrelevant

http://lmgtfy.com/?q=zonal+cavity+calculation

 

[JeffBabineaux]

Thank you. Using the formula from the first link with the tables above, I got a value of 0.07. I assume, then, that these CU values are supposed to be percentages. Also, much appreciated on getting the wording right for a better search. Lighting calculator, lighting layout calculator, and zonal lumen summary didn't turn up anything helpful.

 

[Electric-Light]

Use the RCR and CU in a zonal cavity calculation.

If they are spread out evenly, the angle from a fixture to the working surface is irrelevant

Well, not in "FC" level calculation anyways. Using excessively narrow fixtures cause checkered patterns even though the average foot candle will be the same as if the entire floor was lit up evenly. That's why it's important to look at minimum, average and max as well as a mapped view.

Very narrow beam will produce a high horizontal FC level while depriving vertical FC level. It's quite common for LEDs to claim peak FC values referring to the white part of the checkered board and ignoring the fact that they generate black area as well or conveniently crop out the dark area as unnecessary area.

Uniformly spaced fixtures can still produce uniformly spaced checkered patterns.
The default assumption for office space is 80c/50w/20f. for reflectivity values and it results in uniform lighting.
A basic software will let you hang a 400W MH on an 8' ceiling and it will spit out an average FC value and ignore uniformity issues.

Thank you. Using the formula from the first link with the tables above, I got a value of 0.07. I assume, then, that these CU values are supposed to be percentages. Also, much appreciated on getting the wording right for a better search. Lighting calculator, lighting layout calculator, and zonal lumen summary didn't turn up anything helpful.