9004 is a dual filament bulb that is in-built with a low beam and high beam. When choosing your HID kit, you will need to determine if you want HID lights on just your low beam or your low beams and high beams. If you elect to for both, then you will need to upgrade to the Bi-Xenon HID Kit. Included in your purchase of this HID Kit is a pair of premium ballasts and Xenon HID bulbs, along with necessary installation accessories.