This a high quality product is equivalent to the Philips Xenstart box found on D1S OR D1R bulbs. This base can be used with any D2 bulb to Create the D1 equivalent!! This give you much more choice in replacement bulb. For example: You could fit a Philips 6000k D2s to the D1 base to make a 6000k D1S with all the Philips quality! D2 bulbs have a much wider selection than D1 bulbs. On top of that why buy D1S/R unit (bulb and base) each time when you really only need to replace half of the component? Now you can choose to replace either the bulb or the base! In the long run you will definitely save money through this component. Each time your bulb runs out you can simply purchase an OEM D2S/R and not the whole D1S/R unit and so save £££. For other questions regarding application, Wholesale or other queries please don't hesitate to contact Vincent@HIDorigin.com