Wayne Sallee wrote:
While the watts per gallon rule is not perfect, I find it interesting
when people knock it as being of no value, and then they can't even come
up with anything better.


OK, here is something better - LUX, on a per organism basis. IE: This
acropora needs X lux, that maxima clam needs y lux, etc.

Then one can use any old light meter... er... make that any old WATER
PROOF light meter, to see if the spot they plan on placing the organism
in their tank gets enough light.

Next best thing after that would be lumens per gallon. (I know you said
lumens is percieved light (or something similar) a few posts ago, but
that ain't EXACTLY so. Lumens can be looked at measure of light output
in the visible spectrum -- more correctly called "luminent flux") Lumens
per gallon would indeed be better than watts per gallon.

I would even be OK with the watts per gallon were it to be based on the
radiant flux wattage of the light, rather than the electical consumption
of the light. In fact, this would be the best overall method, since it
would show the true light output of the bulb. But usually, when you see
"watts" listed with a bulb, they are talking about electrical
consumption, not radiant flux.