I specifically said heat bulbs and not hot rocks or undertank heaters for bearded dragons for a reason. Hot rocks can cause thermal burns and undertank heaters make it difficult to regulate the temperature in the enclosure accurately. UVA rays are also delivered to your bearded dragon by using certain heat bulbs.
The bulbs needed to heat an enclosure all fit in the same type of fixture - an incandescent ceramic socket.
Ceramic heat bulbs provide no light to an enclosure but they do provide heat. Just like regular incandescent light bulbs, they come in different wattages. The wattage needed depends on the size of the enclosure and if any other heat bulbs are used. Unlike regular incandescent bulbs, they last for an extremely long period of time, making them more cost effective, but they do not deliver UVA rays. Therefore, these are a heat assist device to a bulb that emits UVA rays (full spectrum flurescent or UVA ray emitting heat bulb). Make sure these bulbs are not placed on a surface that will melt.
As stated before, there are stipulations with using this bulb, but it provides both heat and is a full spectrum bulb.
These are your typical heat lights that emit light, UVA rays, and varying wattages of heat. Different bulb sizes and shapes are available, as well as colors of light (wavelengths). Daylight bulbs are regular white lights, nightlight bulbs are blue/purple lights (make sure the bulb isn't painted blue/purple glass, but in fact blue/purple glass), and nocturnal lights are red (don't use painted bulbs).
The wattage needed depends on the size of the enclosure and if any other heat bulbs are used. The size and shape only matters for fitting in your incandescent fixture.
The shapes of these bulbs usually has a purpose. Basking lights are shaped to direct heat into the area directly below the bulb as opposed to the entire tank, and are usually shaded on the sides to assist in directing the light.
These bulbs do all the same things as incandescent heat bulbs and even though they cost a bit more, they emit more heat, light, and UVA rays than an incandescent bulb of the same size. They also usually last longer and use less energy than incandescents.
Some halogen bulbs fit in incandescent fixtures and others fit in halogen fixtures. Make sure your bulbs fit into your fixtures before purchasing them.