A variety of headlight bulbs are on the market, some that are required by a specific vehicle or motorcycle model and some that give drivers the option of customising their head lamps. H4 and H7 bulbs are high-intensity discharge halogen bulbs, meaning they emit extremely bright light.
H4 bulbs contain two filaments, giving them the option of being either high- or low-beam lights. The bulb has a three-pronged attachment to the wiring harness. Originally developed for European race cars, these bulbs are very bright and can give off white, blue, violet or yellow light.
H7 bulbs contain a single filament. H7 bulbs also come in white, blue, violet or yellow options. The most significant difference between the bulbs is the attachment. H7 bulbs fit different bulb sockets, having a two-pronged plug. Check your owner's manual to determine the type of bulb needed.
Check vehicle manuals before installing new head lamp bulbs. Bulbs with too high a wattage can damage the wiring harness for the bulb and the head lamp reflector. When unsure, contact the bulb manufacturer to ensure vehicle compatibility. HID bulbs are extremely bright and can cause visibility issues for oncoming traffic. When installing the lights, adjust them downward to increase safety for other drivers.