In article , MiamiCuse wrote:

Any idea how to determine how many fluorescent light fixtures I need to
lit a garage 22'x22'x8'H?

I am thinking of getting this:

http://www.lightmart.com/index.asp?P...D&ProdID=19062

Parabolic Surface Troffer 18 CELL 3x32 T8

I wonder if I need 2 or 4 (or more) of these...any thoughts?

There are some different approaches:

1. Suppose you want the garage to be really bright, like classrooms or
brighter retail areas.

How much light is that? One fine day I took a light meter to a big-box
home center, and brighter areas came up around 1300 lux, which is around
120 footcandles (120 lumens per square foot).

32 watt T8 lamps mostly have "design lumens" (light output when of
"average age and condition") around 2700-2800 - I would say 2750 as a
"1-size-fits-all".

The ballasts probably have a ballast factor around .88 for 3-lamp
fixtures (guesstimate). The fixture could trap and lose 10% of the light.
.88 times .9 times 2750 times 3 bulbs is close enough to 6500 lumens.
(You could easily get anywhere from 6000 to 7000 lumens from this
fixture.)

So, to illuminate a 22 by 22 foot area to 120 footcandles requires
58,080 lumens - requiring 8 or 9 or so of these fixtures.

With some light reflecting around from the walls, etc. and lack of need
to have every square foot of the garage quite that bright, you could
probably get that garage nice and quite bright with 6 of these fixtures.
(Though probably a little short of 120 footcandles in most areas and
more than a little short in a few areas)

2. Just get the garage fairly evenly illuminated, as brightly as hallways
in office buildings (roughly 50 footcandles / 550 lux):

It appears to me that 4 fixtures will get the garage fairly evenly
illuminated. Four 3-lamp fixtures should easily achieve 50 footcandles
over nearly all of the garage.

3. See what is done in office areas of office buildings (brighter, maybe
around or over 100 footcandles): What I think is common is for a 4-lamp
fixture to be in a 2-by-4-foot ceiling panel for every 5 of these panels
without fixtures. That is a 4-lamp fixture per 48 square feet.
I suspect your 3-lamp fixture is intended to be used in such situations.

It appears to me that doing this for 484 square feet means 10 fixtures,
and that sounds to me like overkill for a garage.

I would go with #2 (4 fixtures), and have a little task lighting also.

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I would look for fixtures that have a high amount of diffusion or
otherwise are good for lighting wider areas if only 4 are being used,
unless you won't have any problems with uneven illumination. Otherwise
you could need 9 fixtures to get even illumination.

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- Don Klipstein )