BULB DESIGN HP5: Four high-power SMDs, under a diffusing lens. Just like the HP3, but run at higher power, with integrated copper plating for superior heat dissipation, allowing maximum brightness. HP36: Full 360 degree illumination with 36 High-Power Samsung LEDs. Aluminum base for optimum heatsinking, and non-polar design for easy installation. XP50: Each of the four sides of this bulb contains two 5W-rated chips, and the top is fitted with two more under a projector lens. Housed in an aluminum casing with textured finish for maximum heatsinking properties. Fitment. All three bulbs use a quality inject-molded 921 terminal, with a sturdy base connector and proper pin alignment, designed for exact replacement of your factory 921 bulb. You will not need resistors for backup lights. Just replace the factory bulb.