Incandescent light bulbs are very inefficient, which is why they get hot. That's a lot of energy turned into heat not light. Nonetheless us plant collectors have made use of this inefficiency for years. Our home-made "Acme" plant dryer operates using two pairs of 100W light bulbs that provide just the right amount of safe heat to dry specimens in plant presses. When collecting plants you've got lots of drying plant material sandwiched between layers of cardboard, blotters, and newsprint. You don't want to try to heat this to about 50-55C using any heat source that could start a fire. At any rate once you have a light-bulb heated dryer, you just want to continue with business as usual, so when the local big box store puts 100W bulbs on sale, TPP could not resist buying a few dozen bulbs to get us through this season. Bulbs don't last long when they are on 24-7. After this batch of bulbs, well, some other heat source will have to be found.