T8 low bay lights

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la2151

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I have a customer who has existing,400 watt MH low bay lights in diesel truck repair shop.they are spaced fairly normal. 20-25 ft apart & 15-18 ft high.They are not getting enough light at lower levels when working in engine compartment. I am thinking of adding some t8 low bay lights in between the existing lights. I am unsure yet as to number of lamps per fixt.Can use 4 or 6 lamp fixtures. Any others have input or experience with some thing like this? Thanks in advance for any advice.Do I go safe & just use 6 lamp?
 

mivey

Senior Member
Unless you put thought into the lamp choice, the light colors might clash some. If the MH are old, get rid of the MH and put in all flourescent. The energy savings will give a satisfactory payback if the shop is operating regular hours.

Make some light output measurements. A 4-lamp T8 will give you approximately 50% of the light you are getting from the MH. An average MH maintains 24k lumens and the 4-lamp T8 will maintain about 9.5k.
 

Mr. Bill

Senior Member
I just did a quick calc check. With no machinary filling up the room.

Existing install 20' on center: Average 41 fc

Fluorescent replacement 1:1: Average 28 fc.

68% of the light at 40% of the power. You can install 2 fluorescent 6-lamp fixtures for every (1) 400W MH you take out and you'll save 20% of your power and have 36% more light.

Suggestions. You want to keep the lamps as cool as possible (77 F) for more light output and longer lamp life. No lens on the bottom. Cage only if you need to protect the lamps. Vents on the top of the fixture to let air flow thru. You'll have 8 times as many lamps now. Group relamping would be easiest. When about 20% of the lamps die go in and replace everything at once. Otherwise you'll always be replacing lamps.

If you want even less power used do the 1:1 replacement and spend the extra money on task lights about 10' AFF or less at each work station. A 2-lamp industrial. A 50 fc average is a questionable light level for detailed work. A task light should get it to 70-100 fc and use less total power.
 

Johnmcca

Senior Member
We did a job this summer in a small wharehouse and used T5 four tube fixtures. They are advertised to have the same out put as a 400W MH with about half the energy consumption. If I remember it was about 240 wats per fixture. Decent light and good color rendering.
 

mivey

Senior Member
We did a job this summer in a small wharehouse and used T5 four tube fixtures. They are advertised to have the same out put as a 400W MH with about half the energy consumption. If I remember it was about 240 wats per fixture. Decent light and good color rendering.
You can have some glare trouble with T5s in a low-bay situation. They work great for high-bay. I don't think they last as long as the T8s.

We usually recommend a fixture with six 4-ft T8 lamps or four 4-ft high-output T5 lamps as a direct replacement for the standard MH.

Add: Take note that the newer pulse-start MH has a higher lumen output, even more so with an electronic ballast and may require more fluorescents as a direct replacement.
 
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