120 what: watts?
Incandescent bulbs put out a lot of heat, which is bad on its own. And what you really care about is the K rating: you want it to be in the range under which plants grow best (if, as I assume, you are growing macro down there). That's why people get special fixtures.
The most common DIY fixture option that I've seen is a "lights of america" thing from home depot: it has a 6500K flourescent bulb.