These are a special type of incandescent lamp, also known as quartz-halogen or quartz-iodine lamp.
This type of lamp burns very brightly and very hot, and so the glass is made with quartz to withstand these higher filament temperatures.
It is important to never handle these lamps with your bare fingers, as the oils on your hand will leave a residue that will shorten the life of the bulb, and possibly lead to a violent failure of the bulb. To protect people, halogen lamps must be installed behind some sort of glass shield or housing.
What makes the halogen lamps unique is the addition of a small quantity of halogen gas in the bulb. When the tungsten filament burns it slowly evaporates, just like a standard incandescent lamp, but the additional halogen gas combines with the evaporated tungsten and redeposits it back onto the filament. This is known as its regeneration cycle. This has the added benefit of extending the lamp’s usable lifespan and helps prevent the inside of the glass from darkening.
The filament will eventually fail because the tungsten is not redeposited evenly, but typical lamp life is in the region of 2500-3000 hours, and they are an excellent white light source with a high CRI.
While these lamps are suitable for dimming purposes, they must be occasionally be operated at their full rated voltage, as the regeneration cycle requires high temperatures for the halogen gas to bond with the evaporated tungsten. Using a halogen lamp at a reduced voltage for a prolonged time may actually shorten the lifespan of the lamp.