It's not quite that simple because light is refracted and diffuses in
water - it does not travel in a straight line.

Picture the bulb at the apex of a cone of light and the tank bottom as the
base of the cone. OK? Well, that's not the way it happens. Light bounces
around inside the tank in a manner in which I suddenly realize I was
watching the girls in science class the day we learned that and can't
properly describe.

Daniel Whiting wrote in message
...
Well, each half of the 55 gal would be its "own" tank 27.5 gals each,
right? And each section has a 55 watt bulb.. So each side would have 2
watts/gal. The 40 watt bulb means an extra 20 watts are on each side, so
75 watts per 27.5 gals, so 2.7 wpg? Or is my logic flawed?

Richmond wrote:
Just wondering am I (are we) making an error when calculating
watts/gal.

Mine is a 55 USGal tank, 49" length, with two section 24" each
separated by a metal frame. I have two 55 watts PCF bulbs (22"), each
covering a section. Now my tank is 1 watt/gal or 2 watts/gal ??

I also have a 40 watts (48") bulb which covers entire tank. So
logically my tank is 1.7 watts/gal and not 2.7 watts/gal. Is that
correct?

--
Thank You

Dominic
http://www.dlink.org/aqua