Thanks, but that's how I found the light and it's pretty ambigous -

"The Busch&Müller 4DToplight Senso Multi can be powered by batteries or any 6 volt dynamo. Two LEDs in the center, and an LED on each side make for increased visibility. A three position switch allows automatic switching from battery power to dynamo power when you start and stop. And is case of a wire failure, the batteries will keep your taillight "on". The bike must be moving for the Senso function to turn on the lights. So they won't switch on while your bike is parked overnight. Wiring not included. $ 41.50 ".