Commercial space fixture selection and lumens per sq ft calculations

[Stuntman]

I don't do lighting often, but I have a unique job that I am not sure how to approach.

14'6" ceiling, lighting must be surface mounted.
Three unique areas:
Mechanics area
Break Room
Paint/fine assembly area
Machine shop area

In the past, I have historically used 2'x4' 4 bulb troffers and shot for the 75lumens per sq ft +/-. This customer wants 4' LED (2 pin, T8 style) replaceable bulbs, so I can go with the same formula, but unsure if the LEDs warrant changing the setup.

1. Are 2x4 4-bulb LED troffers going to be too bright for a single fixture? I see a lot of 3 bulb and 2 bulb setups, but historically have always used 4-bulb if the ceiling was 10ft or greater.
2. Is there a simple rule of thumb for fixture spacing, particularly one that takes into account the ceiling height?
3. Is there a better lumen calculation for these unique lighting spaces (break room vs machine shop, etc)?

Thanks in advance.

 

[hbiss]

This is where a lighting supplier can help you.

-Hal

 

[electrofelon]

I don't do lighting often, but I have a unique job that I am not sure how to approach.

14'6" ceiling, lighting must be surface mounted.
Three unique areas:
Mechanics area
Break Room
Paint/fine assembly area
Machine shop area

In the past, I have historically used 2'x4' 4 bulb troffers and shot for the 75lumens per sq ft +/-. This customer wants 4' LED (2 pin, T8 style) replaceable bulbs, so I can go with the same formula, but unsure if the LEDs warrant changing the setup.

1. Are 2x4 4-bulb LED troffers going to be too bright for a single fixture? I see a lot of 3 bulb and 2 bulb setups, but historically have always used 4-bulb if the ceiling was 10ft or greater.
2. Is there a simple rule of thumb for fixture spacing, particularly one that takes into account the ceiling height?
3. Is there a better lumen calculation for these unique lighting spaces (break room vs machine shop, etc)?

Thanks in advance.

A common spacing I do in the labs I set up are 2x4 panels, with 4 feet between lights in the long direction, and 6 feet in the short direction. So that is one panel for 64 sq feet. I Cant remember the exact # of lumens these panels are, but usually they are around 6000. That puts us at 94 lm per sq foot. We go fairly bright in these labs. I have frequently done 4 retrofit tubes in a troffer and its totally fine, dont worry about it. Your typically 4' tube is 1900 lumens, so 7600 for 4, but you will lose some with the diffuser. I would have not problem using 4 per and just shoot for that 75 lm/sq ft figure so each fixture in a 100 sq ft square (or rectangle). I always tend toward higher, its never really too bright.

 

[Stuntman]

Thanks electrofelon, that gives me a place to start. I also notice that 6 bulb T5 style fixtures are becoming widely available and can be LED converted. Based on your comment, 6 bulb may not be too many?

 

[electrofelon]

Thanks electrofelon, that gives me a place to start. I also notice that 6 bulb T5 style fixtures are becoming widely available and can be LED converted. Based on your comment, 6 bulb may not be too many?

I don't think it would be too much as in annoyingly bright to look at, but might push you into a a rather large distance between fixtures and uneven light distribution, assuming you keep the same number of total lumens. I do always like flexibility though, perhaps an option is to use 6 bulb fixtures but only plan around 4 in each. Could throw another tube or two in later if you find yourself needing more light. Of course you could just get higher lumen tubes if you only had four tube fixtures and find yourself needing more light.

 

[EngineeredElectric]

Important note:
TLED bulbs are much better at getting the light to the floor than fluorescent tubes because TLEDs are directional. Not sure if your 75l/sqft figure included reflection losses, but in my experience 3500lumen TLED's replace 5000lm fluorescent tubes and result in the same light output on the ground. Adjust your expectations accordingly.

1. Are 2x4 4-bulb LED troffers going to be too bright for a single fixture? Not in my experience I see a lot of 3 bulb and 2 bulb setups, but historically have always used 4-bulb if the ceiling was 10ft or greater.
2. Is there a simple rule of thumb for fixture spacing, particularly one that takes into account the ceiling height? Spacing is a function of desired lumens per sqft (fc) and lumens per fixture, so the rule of thumb is to space the fixtures according to your desired lumen density on the shop floor
3. Is there a better lumen calculation for these unique lighting spaces (break room vs machine shop, etc)? 50fc for general warehouse, 75 for fine work, 100 for very fine work. Adjust slightly for walls, storage racks, shelving, ect. Vertical surfaces absorb light just as they absorb sound.