radiant heat

"How hot" isn't really part of the equation, though I supposed that that's an interesting question in and of itself; how hot does a light bulb get?

It depends on the distance between the heat source, in this case, a 60 watt bulb and the material and, of course, the type of material; a piece of 2x4, I'd say, a long long long long time.

I hope this is strictly for academic/theoretical purposes, Chasman.

You can set a towel on fire by draping it over a lamp with a 60 watt bulb, but it will take a few hours.

There are several things you need to know to solve your problem. First, what are you trying to set on fire? At what temperature will it spontaneously combust? How close it is to the bulb? (You should assume the bulb will radiate in all directions, so the proximity to the bulb will determine how much of that 60 watts is getting to the flammable material.) Finally, how fast is the material losing heat? A lamp shade could catch fire, but it is continuously shedding heat to the air.