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#40068 07/11/04 11:47 PM
Joined: Dec 2001
Posts: 15
Got a lighting RFQ for a new laundromat (100ft x 28ft x10ft high). The owner thinks that 8 fixtures (2'x4' w/4 lamps) will be enough. Does anyone have a link to a site that has footcandle recomendations?

Joined: Apr 2002
Posts: 558
I don’t have any good recommendations for sites to check but hopefully one of the other members can help you out. I will tell you that if this project was in California you would be allowed to use 2520 watts maximum to light this area (2800 x .9watts/sqft). Using the allowed watts for a given area usually gives a pretty good idea of how many fixtures will be needed. I would guess that it will take closer to 20 fixtures to light this area.


Curt Swartz
Joined: Mar 2002
Posts: 582
Ron Offline
See the table about 3/4 of the way down the following site.

Joined: Jan 2001
Posts: 1,044
Tom Offline
20 fixtures looks about right for 30fc maintained.

8 fixtures will result in very uneven lighting & will get you about 18fc. Was the owner previously an owner of a movie theater? They were also notoriously stingy with light.


Few things are harder to put up with than the annoyance of a good example.
Joined: Dec 2001
Posts: 15
How did you arrive at these numbers?

Joined: Jan 2001
Posts: 1,044
Tom Offline
I've trained a spreadsheet to calculate room cavity ratios. Using a 10' ceiling height and an assumed workplane of 30" above finish floor and the other room dimensions you listed, the RCR came out at a little under 2.

Then, I pulled out a really old lighting design book (Rapid Lighting Design and Cost Estimating by Prafulla C. Sorcar, P.E. copyright 1979), looked up the 2x4 fixture curves, assumed 30 fc & read the curve over to the square footage per fixture, divided that into your square footage which worked out to fixtures.

As for the 18fc estimate, I did the same thing backwards by dividing the square footage by # of fixtures, read over to the curve & up to the fc.

I'm not sure how accurate this book is, but I've never had any complaints about things being too dim.

BTW, Prafulla has published other lighting books & is multi-talented, visit his site at

[This message has been edited by Tom (edited 07-12-2004).]

Few things are harder to put up with than the annoyance of a good example.
Joined: Aug 2001
Posts: 458
go to You can download the simply indoor lighting calculation software with photometric data.

This will let you see a suggested layout with lighting values for your project. Other lighting manufacturers have photometric data for their fixtures for download that can be used with this also.

Joined: Feb 2002
Posts: 182
Bob Offline
I ran your room size using the Hubbell
Software. For 25 footcandles you would need
2 rows of 6 fixtures.

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