European vehicles equipped with HID headlamps are required by ECE regulation 48 also to be equipped with headlamp lens cleaning systems and automatic beam levelling control. Both of these measures are intended to reduce the tendency for high-output headlamps to cause high levels of glare to other road users.

http://en.wikipedia.org/wiki/Headlig...nd_Bi-Xenon.29

Geez kym, how hard is it to use the search button!? :P (google)