Originally Posted by the_ulf

where to begin...
it all depends on what type of lamp the vehicle is looking for. LED or HID retrofit kits to replace an incandescent element would usually include a shunt of sorts (simplified) that would fool the module into seeing an intact lightbulb. i'm presuming you're planning to replace pre-LCI halogen halo with an aftermarket LED.
apart from the subject already having been discussed to death several times over on various BMW forums you also didn't really include a lot of info about the vehicle you're talking about which doesn't help either. general consensus seems to be to go with the LUX kit. or buy the ebay special and report back how it's going and how long for.