T-8 Florescent strips

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nizak

Senior Member
Am looking to light an open shop area that has 9' drywall ceilings painted white. Dimensions are 30'x40'. Would like some help(possibly a formula) to determine amount of light needed. Fixtures will be 8' florescent open strips total of 4 48" tubes per fixture(referred to as tandems). Lamps are 32W 4100K. Owner wants it to be "very bright", I realize that this request means something different to everyone, but a starting point would be helpful. Thanks.
 

greenspark1

Senior Member
Location
New England
There is a formula to use but I only learned it to take the PE :)

'Very bright' is pretty vague. What types of activities? 50fc is a good starting point but levels can go up quite dramatically if you're working on detailed objects with low contrast or have old eyes. Think paint shops, operating rooms, sports fields etc.

Here is an online tool from GE: http://www.gelighting.com/LightingW...sistant-toolkit/lighting-layout-estimator.jsp
With your parameters and 50fc it estimates 9 fixtures. Again, depends on what brightness you need/want. If you don't always need it super bright you could have a dual switched setup that turns on half the lights at a time.

If you want more precision and more control, the program Visual from Lithonia has a free 30 day trial and is pretty quick/easy to use. They also have tutorials to get started. Link here: http://www.visual-3d.com/software/download.aspx
 

rdevarona

New member
To add to greenspark1's reply, Visual also has a free web-based Visual Interior Tool that gives pretty good results for quick jobs like this one. I would typically light a shop to 50 fc as well. I've had a couple of customers ask for showroom-level lighting for their man caves, so we've gone as high as 100 fc before. Here's the output from the tool for your shop assuming a 50 fc target:

30x40x9_Shop_50fc.jpg

If you went with 3 rows of 4 fixtures each, you would get 78 fc on average.
For 3 rows of 5 fixtures each, the level goes up to 98 fc of average.

Regards,

rdv
 

jcbabb

Member
Location
Norman, OK, USA
To add to greenspark1's reply, Visual also has a free web-based Visual Interior Tool that gives pretty good results for quick jobs like this one...
rdv

It is important to note when using this software to always enter a value of less than 1.0 for the "Light Loss Factor" input variable. I generally use 0.75-0.8 for fluorescent fixtures, and it appears that rdevarona has done so as well.

This obviously isn't an extremely precise calculation with so many unknown variables, but a proper LLF will get you a calculation more in the realistic ballpark.
 

greenspark1

Senior Member
Location
New England
It is important to note when using this software to always enter a value of less than 1.0 for the "Light Loss Factor" input variable. I generally use 0.75-0.8 for fluorescent fixtures, and it appears that rdevarona has done so as well.

This obviously isn't an extremely precise calculation with so many unknown variables, but a proper LLF will get you a calculation more in the realistic ballpark.

Good point.
What LLF do you typically use for LEDs? I go with 0.9 due to less lumen depreciation.
 
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