I believe that floaters like a lot of light, so if you have dimmer lighting, then you will need to minimize the distance, while you may allow extra room for a brighter light if you would like.

 

depends on the light and tank. A small tank with one light would need enough distance to spread et cetera. But most set ups have the lights high enough that it isn't much an issue. Aside from that you don't want hot bulbs an inch from tender plant leaves.

FWIW - I keep my lighting 4 inches from the water on my main aquarium and have riccia floating.

 

I have a 20 long with a single 18w tube about 4 inches above and everything I have thrown in there so far grows good and no algae. From day one with this setup I have had next to zero issues. I have a bunch of hornwort floating.

 

i have red roots, light is like 5-6 inches up
i have salvinia and light is like 10 inches up
growing well ...

 

I am glad I saw thispost, because I have a T12 bulb coming for a 10 gallon that will have najas grass, and Ihave not yet figured what kind of lighting fixture to use. I was going to get a strip light and lay it on top of one of a glass top, but that now seems too close. I would love a different way of mounting it because I was afraid one of my cats would knock it off.

 

i've got a hardware store clamp light with a 23w cfl clamped onto a lamppost next to my 10g. if your new bulb would fit into a clamp light, that might work.

 

a t12 would probably not burn any plants. I use 20W of CFLs over my ten, it's about 1-2 inches from the top, and everything does fine.

 

Awesome. Thanks.

 

I have 2 55w Power COmpact Fluorescent bulbs that actually throw a reasonable amount of heat. I've got had trouble with floating plants in the past and as I've been thinking about it, I think it is because when I top off the tank I'm filling it too high. (the light fixture sits on the top of the tank). That's the main reason I asked. Right now the plants are probably about 2 inches or so below the light and seem to be doing fine.