i definately want to use the 8ft. those 110 watt fixtures were very bright. i think if i run 2 rows evenly spaced with 6 per row i should be good. now all i need is some $$$$$$$

 

I'd price the 8 foot replacement lamps verses the 4 foot ones before you buy. There maybe a large price difference.

 

Not to mention storage... I buy lamps by the case. 4 footers are much easier to handle than 8' footers... Plus, it's simple enough to stick two 4' fixtures end to end.

 

in a 30 x 60 building it would take alot of lamps to light up that area, plus the 8ft are commerical quality and are built to last longer....

 

Just a little info provided from a study that a textile manufacturer I used to work for did: The optimum height for florescent fixtures to be most efficient is nine feet from finished floor. This is for eight foot, double tube fixtures with the curved reflection pans installed.

 

For kicks, I just ran some calcs on a 30x60 room using a vendor program I have on my computer here at work (this is sort of what I do for a living...).

With 8' 2-lamp strips, you can get about 72 foot candle average w/ 12 fixtures in a 3x4 pattern at the previously mentioned 9' height. Bump it up to 12' and the levels drop down to about 65 fc. 2304 watts total.

 

Independent of how many fixtures you use is the question of which bulbs you use in them. I had normal warm whites (4 footers) rated at 34w originally but they just didn't cut it. I tried the cool whites which were marginally better. Then I went to the more expensive 40w (non energy saving) high intensity "daylight" bulbs which made a huge difference. In the garage I'm more concerned with being able to see as opposed to saving money so in my mind it was worth it, "see" my point? :-)

 

Depending on the age of the fixture, you may not have been able to use 34W bulbs. It depends on the ballast, but they are not always interchangable. We have some older 4' fixtures in the garage and the previous owner tried to use 34W bulbs - they were not very bright and burned out rather quickly. The ballasts were not designed to power the 34w bulbs. I swapped them all out to 40W bulbs and in addition to greatly improved light levels - much more than the 15% increase in wattage - I haven't replaced a bulb all year.

 

Good point, I never realized that. My fixtures are quite old so that may have been part of the problem. Thanks

 

i'm looking at the 110 watt commerical high output cold start 8 ft fixtures. i think those will definately outperform the smaller ones. that would make a big difference on the light pattern also...

 

Oh yeah... before we (I) derailed your thread, that was your initial question...

My calculations above were done with a 3 row layout, 10'x14' on center. Depending on how high you mount them and the reflectances of your ceiling, walls and floor, you'll get a lot of light.

I would strongly recommend tube-sleave guards as well.

 

Fluorescent T8
Dimmer ballast
Section the system

 

Anyone have experience with metal halide shop lights?

 

My shop has 10' ceilings. Do you think that's too low for low bay metal halide lights? I'm thinking it probably is. I haven't seen any low-profile MH lights.

 

Probably. They make them low profile, mine aren't. They are about 18" tall. I actually built little boxes for them to recess into the ceiling.