Always change in pairs!Philips Xenon HID lamp D4SXenon HID lamp D4SPhilips Automotive, XenonPhilips Xenon HID lights deliver twice as much light as halogen bulbs but consume less power. This offers drivers enhanced visibility while allowing the vehicle to save electrical power for other functions. With twice the amount of light you can see potential obstacles much sooner. At highway speeds, HID lights give you up to a full second more time to safely react to road hazards.Xenon HID lamp