I agree with the difficulty in lighting a deep tank. But in general,
the watts per gallon relationship only holds for a fairly narrow
range. 3 W/g is insufficient for a 3 gallon tank, just as it's more
than you need for a 125 gallon.

I'm not disagreeing with that. Have you seen the article this page was based
on?

http://www.thekrib.com/Plants/Tech/Lighting/

It's true, the wpg relationship is true only for tanks in a certain range --
but a 65 gallon tank falls in that range. If anything, a 65 gallon tank needs
more light than the rule of thumb suggests, probably because of its depth.

He even includes a calculator showing the amount of lighting Amano
would probably use on a given size tank. For 65g, it says 155W (or 2.4
W/g). For 29g, it's 107W (or 3.7 W/g). So if you believe all this,
Almazick is actually slightly understating the lighting equivalence
between 29 and 65 gallon tanks.

I'm afraid I don't buy that calculator. I don't think a "best fit" curve is a
good idea for making recommendations for specific tanks. While it's
interesting to see the whole picture on a graph, a best fit curve interpolates
for areas where there's no data, and forces data to fit in areas where it
doesn't. It's a best fit curve, not an *actual* fit.

While I have no argument with the general premise of the page, I think his
calculator is flat wrong for a 65 gallon tank -- probably because the
calculator doesn't take into account the depth of the tank.

A better calculator would take into account the depth of the tank, the length
of the bulbs (longer bulbs produce more light for their wattage), and the
surface area, not just the tank volume. And probably the efficiency of the
reflector.

Okay, that's probably not practical. But I think there's good data in the Krib
lighting survey, because it shows what people are actually using for a specific
size of tank. I suspect that's more useful than any rule of thumb or best fit
curve could ever be. The logarithmic scale is difficult to read for many,
though. Rather than a calculator or a graph, I'd do a table, showing the tank
size, lighting range, and average lighting. So you could just look up your
tank size and see how much light other people are using.


Leigh

http://www.fortunecity.com/lavender/halloween/881/