Take a look here: StVZO Beleuchtung und TA Bestimmungen. The page refers to the "TA" rulings, which are the "technical requirements" guidelines which tell you how to test the stuff defined by the StVZO to get the stuff approved by the "Technisches Bundesamt".

Look under "TA 23: Beleuchtungskörper" - there is a picture which shows how much or max. light (in lux at 10m) is allowed in the different quadrants.

Greetings,

H.C.