Although HID lights have only recently come available for a number of different uses, such as for headlights, the idea behind the lights has been around since the 18th century. HID light bulbs create an electric arc though tungsten electrodes that heats metal ions to the point of becoming plasma, giving off a bright blue-white light. HID lights are quite different from incandescent and fluorescent light bulbs, and their use has disadvantages as well as advantages.
Pro: Greater Briliance with Less Energy
HID bulbs provide greater illumination at much less cost in energy than incandescent bulbs. They release more radiation as visible light instead of heat. They also provide greater illumination than other low-energy lights like fluorescent light bulbs. As a result, they have often been used for large open areas, like stadiums.
Pro: Clearest Lighting for Driving
HID lights not only provide more light than other light bulbs, but also emit light toward the blue-white end of the spectrum, which is more easily seen by night time drivers. They light up the area ahead of a car more clearly than conventional lights.
Con: Less Natural Fade
HID lights have less fade between the beams of light and the surrounding darkness. This can be a disadvantage when driving on uncertain and winding roads. The area around the beams will not be visible at all, whereas incandescent lights, while not as bright, would illuminate more of the area around the beams.
Con: Glare
The largest disadvantage for HID lights is the glare that drivers who are driving in the opposite direction experience when they pass a vehicle with HID lights. Because HID lights emit light closer to the blue side of the spectrum, which is more visible to drivers at night, the light comes across as painfully blinding to other drivers.