Incandescent bulb are black body emitters. Basically, something is heated enough so that it radiates most of the power put into it. The black body radiation spectrum is well known, with it being a function of temperature. The lower the temperature, the more the bulk of the radiation shifts to lower wavelengths.
Normal incadescent bulbs used for lighting are actually horribly inefficient. We don't have a material that we can heat up so hot to maximize the amount of visible light in its black body radiation spectrum. Actually, we can heat material that high, but it won't last long. We don't have a material that won't evaporate or sublime slowly enough to make a useable lightbulb with its black body radiation optimized for visible light.
Real LEBs (Light Emitting Bulbs) are a tradeoff between efficiency and lifetime. The hotter you run the fillament, the more efficient but also the shorter it lasts. This effect is quite non-linear. A little hotter makes a big difference.
There is therefore another reason to have separate heat lamps from ordinary LEBs, which is to make a more economical IR emitting bulb. The fillament operating temperature is adjusted for good IR production and less light. This does increase efficiency a little, but a ordinary LEB still emits most of its radiation as IR already. However, running the fillament cooler greatly increases bulb life and forces less tradeoffs in the design otherwise. Not only does the fillament evaporate slower, but the wire can be thicker, for example.
So dedicated heat lamps are a little more efficient at their intended purpose, but also last a lot longer and are more rugged and durable than incandescent bulbs shifted more towards producing visible light.
