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Re: proper lighting

On Mon, 18 Oct 1999, Marc Radle wrote:
> I'm trying to grow live plants so I want to have the
> "correct" amount of light. If memory serves, the rule is 3-5
> watts per gallon, right?

Erik Olson supplies an excellent summary on lighting needs as a
function of tank size at:


Successful plant tanks work with anywhere from somewhere 1.5 watts per
gallon to over 8 watts per gallon.  There seems to be a systematic
variation (especially in Amano's tanks), with miniature tanks needing a
lot of power per gallon and larger tanks needing much less.  Speculating,
I think that's because in smaller tanks, a lot of the light "spills" out
of the tanks without doing the plants any good, while in larger tanks more
of the light is used in the tank.  In short, big tanks are more efficient
than little ones.

I can imagine that tanks with a big foot print and shallow water will be
more efficient at using light than are tall, narrow tanks.

Of course, it could just be because it's easier to get a lot of power per
gallon on a small tank then it is to get it on a big one.

> If this is correct, that would mean my tank ( a 42 gallon
> Oceanic Systems Hex ), would need at least 126 watts !!! My
> light hood has one spot for an 18" bulb and all the 18"
> bulbs I've seen are 15 watts !!! How the HECK do I get that
> much light ?!?!?!?!?

Sounds like that hood has got to go.

Sorry I can't help with details on that tank, but from Erik's article and
the shape of your tank I guess that you may need at least 126 watts of
light if you want to grow a wide variety of plants.  The normal options
are small metal halide pendants or DIY hoods using compact fluorescent or
power compact tubes.

Roger Miller