Everybody stay calm.  Please, people, work with us.  We're just a few non German speaking, burrito eat'n, pizza order'n, soy sauce dunk'n, Sriracha squirt'n, Americans who only speak English, but could probably ask for a library in Spain.  Who knows what Busch + Muller are trying to say.  For that matter, who knows what B+M's co-conspirator, Peter White, is trying to say.  It's a Dynamo light for the rear of your bike!  It helps to make you visible in the dark.  It will emit light in 320 degrees.  The missing 40 degrees is the back of the light which faces the front.  So use your front light to illuminate the road ahead of you, not the tail light; it's just 40 missing degrees.  What we gather is that this light actually refracts brighter the nearer oncoming light approaches. New "Brake Plus", light senses dynamo slowing and glows brighter.... Can you say AWESOME! Spend 320 business hours researching before ordering. Wiring not included.  
Requires two mounting holes spaced at 50mm or 80mm.  Mounting brackets are available.