There are many types of headlight replacement bulbs on the market. If your car came with factory HID, then you will be looking at the below list of bulbs available for you. Each type is available as OEM factory and aftermarket models. HID bulbs come in Four main variations. D2S bulbs are used for HID projector use. D2R bulbs are used for HID reflector use. D1S bulbs are basically D2S bulbs with built in igniters, and are made for HID projector use. D1R HID bulbs are similar to D2R bulbs with built in igniters, and are used for HID reflectors. HID bulbs have a capsule filled with a mixture of noble gasses and metal halide salts. The replacement ballasts send a startup current through the bulb, which arcs across two electrodes on each side of the capsule, creating light. HID bulbs have a very long life span of around 2500+ hours. Compare that to a standard halogen bulb which generally only lasts around 300 hours. Replacement Bulbs come available in many sub-variations too. You can select from higher lumen output versions such as the Philips 85122+ to ones with more or less of a kelvin (color) temperature. As a rule of thumb, the higher the kelvin rating of a bulb, the lower its lumen rating. So a bulb that is a 4300K pure white will be significantly brighter than a 12,000K purple bulb. True HID xenon bulbs are better than normal halogen bulbs in every way.