A digital high intensity discharge (HID) kit is used to convert conventional car halogen headlights so they emit a high-intensity discharge. HID kits are controversial and banned in many countries because they produce a concentrated glare that can temporarily blind other road users. The “digital” aspect is little more than a marketing term used to try and legitimize this kind of kit, claiming that is has a “slim ballast.”
- The filament of a halogen bulb is a coil that produces its greatest light intensity at the center of the filament. HID bulbs, on the other hand, are lit by two electrodes on either end of the bulb which light up a gas such as mercury vapor. For this reason, they are brightest at each end. This makes them suitable for lighting large spaces such as sports fields efficiently, but unsuitable for specially directed lighting.
- Because of the great difference between halogen and HID bulbs, HID kits can actually reduce the functionality of car headlights. This is because the reflectors and controls in car headlights are designed for light emitted by halogen, not HID bulbs. Installing HID bulbs can lead to emission of unwanted glare, loss of the “bright” setting and even a reduction in visibility.
- Because of their potential for being a hazard to on-coming drivers, HID kits are illegal for use on cars in many countries, including the U.S. The European Union says that use places other road users in “extreme danger” because of the increase in glare.