In article , Ignoramus20878 wrote:

Thanks. I am very interested in this. I am very tired of working under
less that ideal lighting. Would you say that a 400W bulb provides
"ample" light for a garage? (say 20 x17 feet, drywall) Or would you
say that going higher may be warranted?

Now, I gotta remember how many square feet is usually illuminated by a
quad 4-footer in typical office space... Maybe 96 square feet, maybe even
less.

I do remember calculating that typical lighting levels from overhead
lighting in office space was generally in the range of 110 to 200
footcandles (lumens per square foot). A quad 4-foot fluorescent fixture
typically produces around 11,000 lumens (13,000 lumens for no light losses
with brand=new 40 watt bulbs). One of these per 96 square feet would
achieve about 115 footcandles... Maybe common is a quad 4-foot fixture
per 64 square feet, which would achieve about 170 footcandles.

(Going by lumens per square foot, not actual photometric readings.)

A 400 watt metal halide produces about 40,000 lumens - figure more like
35,000 once the bulb has aged somewhat. 20 by 17 feet is 340 square feet.
Assuming good reflection of light hitting walls and even light
distribution, the illumination level would be on the low end for office
lighting.

What I would be afraid of is that the light would not be distributed
well and would hit many work surfaces at a bad angle. Unless temperatures
are unfavorable for fluorescent, you are probably better with an adequate
number of fluorescents - 12 to 20 4-footers to achieve an illumination
level like that in an office. If you use 400 watt metal halide, 1 may not
do well, you may need two.

- Don Klipstein )