What kind of tank/hood is it? I have an Eclipse 5 gallon hex tank that came with a 10 watt 5000 or 5500K bulb and it was so bright. It was almost too bright for me just looking at the tank! I removed this bulb and added a 7 watt/ 5000K bulb and it's perfect. Just right for plants and not too bright for the betta or me. The betta started to sit in his java moss bed that was up near the water line, instead of hiding on the bottom.
This new bulb fits into the hood, and I called and made sure it would be ok. The bulb is a compact fluorescent with a screw base. The only thing they said was don't put the bulb on a timer or dimmer. I did want to put it on a timer, but I guess it didn't matter either way. I have other tanks that I can't use a timer with either so I turn them all on and off myself.
Here's the bulb I got: http://www.bulbman.com/index.asp?Pag...OD&ProdID=4160
On the left, click on "Compact Flourescent -- Screw Base" to see more. There are CF
-- spirals, torpedo, A shape, etc.
As long as the bulb you have doesn't get too hot in the hood, and it fits, I think it's ok. I had my replacement bulb in for a few months and it was fine.