Ever since BMW launched the 1 series facelift and EfficientDynamics on quite alot of cars in their range in 2007, BMW also has started to use LEDs in different places to replace the old incandescent bulbs.
One such location are the license plate lights. BMW employs for all their recent models now a version with two integrated LED bulbs which give a whiter kind of light, even with a hint of blue.
Tuning and styling fanatics of course wanted to mimic this new style (and the use of LEDs on competitors such as Audi’s headlights) and a few aftermarket options are already available for the BMW range.
However, if you get the correct parts, the OEM BMW parts can be fitted on cars which did not come with the LED versions of the license plate lights. This can work for pre-facelift 1-series and pre-EfficientDynamics 3-series cars, but also for 6-series and even the previous model Z4.
People at the z-roadster.net forum were so kind enough to draft a manual on outfitting your Z4 with these OEM LED lights. The text is in german, but the included pictures make the modification self-explanatory.
Get the manual: Install OEM LED license plate lights.