This doesn't mean CO2 can make up for insufficient lighting. The
light needs to be at least enough for the plants to grow.

Chuck Gadd
http://www.csd.net/~cgadd/aqua

So - what IS sufficient light for plants to grow ? I'm having a hard time
establishing plants in my tank. Even hornwort is dying - all the little
needles are littering the bottom of my tank. I've ordered a CO2 system -
it's on its way. But I know I need to change my light, I just don't know
how.

I have a 55gal tank - it's 48" long, 20" high and 12" deep. I have a
stanard one-bulb hood on it - the kind where there are 2 lids you can lift
at the front to feed the fish. Right now I have one 40-watt bulb. Is there
some formula for figuring out wattage ? Can I buy a 75-watt or a 100-watt
bulb for this one-bulb hood ? Do I need a new hood ?

Thanks for any and all advice.

shawn