Unca Sam got it mostly right. Busch & Muller Ixon lights are zehr gut. I'm using the bottom of group Ixon Core which has been just great 4 years now. Low setting is usually good enough, high setting lights up the road ahead well enough for most bicycle speeds. Fast downhill you would want more. Totally reliable, simple as could be. The wife has had hers two years now and she is as happy as I am.
However. We tried the next light up, the Ixon IQ Premium with the 4 AA batteries. Flimsy plastic case. Supplied mount did not work at all, American distributor quickly supplied replacement. Worked OK but never felt solid. Then it was left in a drawer for the long days of summer. The batteries went dead. OK, recharge them. And the light would not work at all. Contacted B&M and was informed if the batteries ever went dead the electronics were fried. (Not given information in original instructions) And since we were responsible for letting the batteries die no warranty coverage at all. American distributor concurred with that. Out $100.
Even after that dismal experience we could not find a better light for our purposes than the Ixon Core so we got another. Included lithium battery does not expire over summer. Lithium battery works better in cold than most.
Top line Ixon Space light is expensive. Looks same as Ixon Core but much bigger. Throws as much light as a car headlight. Legal in Germany of course.