Garage/Shop Fluorescent lighting requirements (Watts, lum)


Old 12-29-04, 09:46 AM
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Garage/Shop Fluorescent lighting requirements (Watts, lum)

I am planning the lighting system for a 3-car garage with dimensions of about 24 by 36 feet (864 ft^2).

Two of the bays will house one vintage car and a full array of tools. The third bay will be used to house a commuter vehicle.

I want a lot of light for the two bays where automotive restoration work will take place. I may still need a work light for when I work under the vehicle but I perfer not to. I want the work space to be like a lab and it will be kept in a very clean manner (I might even end up with a black and white checkerboard floor).

From what I have been able to find, retail space (I guess in a store looking at goods) should be about 4 watts/square foot. That seems to be the highest listed application.

So my math gives (864 ft^2)*(4 Watts/ft^2) = 3456 W

Does a fluorescent fixture with 4 40 watt bulbs equate to 160 Watts total?

If YES; then I would need to install 22 (rounded up) fixtures, right?

That seems like a lot. Especially at the home depot price of $137 a piece ($3014 total) Maybe I don't need that much illumination. But even if I cut the figure in half, we are still talking about a grand and a half. Maybe this is just the way it is if I want proper lighting.

Does anyone have any practical experience in this arena? Maybe a cheaper place to buy them? Is my math completely wrong?

Old 12-29-04, 11:37 AM
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You can download the lighting calculation software and see the lighting levels by choosing different fixtures and changing the number of fixtures.

Unless the garage will be heated you will probably need HO (high output) fixtures so the ballast will strike in the colder months.
Old 12-29-04, 08:21 PM
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Fixtures with T-8 lamps and electronic ballasts will also start at low temps - less expensive than HO fixtures. Look for fixtures with four 4' lamps, either side by side or in tandem (4 lamps @ 32 watts) + (22 watts for the ballast) = 150 watts per fixture. 22 watts is approximate - ballasts vary a bit but it's an inexact calc at best so 22 watts works fine.

4 watts per sf is mighty high. I've seen showcases wired to that level, but never a whole store. 2-3 w/sf would be more common, but in most stores they have display areas lit to higher levels.

Will you be finishing the ceiling? If you will, the most effective way to do this will be with 2x4 drop in light fixtures designed for suspended ceilings. A four lamp fixture of that type should run you about $50 with lamps. You can get rough-in plaster frames for most brands that allow you to install them flush with a drywall ceiling in a tidy fashion. If you're handy, you can cobble up a similar frame with ceiling angle and wood framing. Be sure to test your handiwork to assure that you can get the fixture in the frame before the drywall goes on.

8' "tandem wrap" fixtures will work as well - 8 ' long fixtures with either 8' T-8 lamps or 2 pairs of 4' T-8 lamps in each fixture. These are available as open-lamp fixtures, but for a high-end installation like yours, I would use the sort with diffusers. They're more $ than 2x4's - $110-130 with lamps if you shop around.

There are several other considerations:

Overall square footage is 864, but how much of this is built in cabinets that won't need light? How much is bench space that will have it's own (generally undercabinet) fixtures?

What color will the space be? White spaces need far fewer fixtures than dark-colored ones. Ceiling color is important. Wax the floor for more light yet.

How high is the ceiling? Really high ceilings need more fixtures, and if your ceiling is 14 foot high or better, I'd consider 250 watt lo-bay metal halides rather than fluorescents.

What does the ceiling framing look like? Sometimes fixture layouts and quantities are dictated by framing constraints. You can get by with a lower overall light level if the lighting is even - how many can you lay out evenly?

What power is available? The max number of 4 lamp, 4', T-8 fixtures you can put on a 20 amp, 120 volt circuit is 12, and then only if you use a 20 amp switch. If you use a 15 amp circuit, the max is 9.

So - how many fixtures? There are proper calculations that take in to consideration things like room cavity ratios and reflectences, but in the end I suspect you will come out with something like two or three watts per square foot if you use white walls and ceilings with a checkerboard floor. My garage is lit at 2 watts and I find it acceptable but not spectacular. My floor however, is a dull gray, and the ceiling is unfinished. I have gray shelves down one side, filled with brown boxes that suck up the light on that side. It's pretty bright even at that - if it were white it would be very bright indeed.

Assuming 2x4 fixtures on an 8' white ceiling with white walls then:

2 watts/foot is 12 fixtures - an easy number to lay out and only one circuit, but perhaps a bit shy of your expectations. 3 watts/foot would be 17 fixtures - a difficult number to lay out. I might go with three rows of five fixtures if it were me. Use two circuits and a minimum of two switches, perhaps with the commuter car storage area on it's own switch. Three rows of six fixtures would be deluxe, indeed; overkill IMHO, but everyone's opinion of "enough" light is different.

Allow for a trouble light on a cord reel, just in case.

Post pictures of the shop when you're done?

Last edited by Cheyenps; 12-29-04 at 08:31 PM.
Old 12-30-04, 09:58 PM
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i have a 24x28 finished inside with 8' ceiling.i got them with two light that are 4'long at lowes with the plug in on them,just cut them off and wired it in.i have 8 of them and they are walls are a med gray,ceiling not panted.these were about $10.00,and they work good in cold to.

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