You could also put the light in an enclosure so that you just get the heat from the bulb like this guy. http://brewstands.com/fermentation-heater.html
THAT, looks dangerous. I have done enough elecrical work to know that an un-grounded lamp cord in a metal can that can...
"bring the temp up from 58 to 68. and it only took a couple hours with a 60 watt bulb " site quoted
is asking for a fire or just a bit less bad, a tripped breaker on the fridge.
If I were doing the "bulb in a can" thing I dont think I'd go over a 25watt bulb.
I was thinking the same thing. That plan is so unsafe. Why not just use a heatwrap in the enclosure?