I use several of the Busch and Muller lights. If I understand correctly they require a proper beam pattern. I currently use the Lumotec IQ Cyo, Lumotec IQ Fly, Lumotec Retro, and the Lumotec Round. The last two are halogen but still have a decent beam pattern, but cannot compare to the LED's for light output. I also have several of their tail lights. AFAIK I will never use anything but Busch and Muller lights on my bikes. Not only are they great lights I can order parts for them! I only buy the head lights and tail lights that have the stand light function, some of mine have the Senso feature that turns the lights on and off automatically, I like it, but don't have to have it.

Aaron