Originally Posted by jputnam

It's not just the lumens, it's the beam pattern. Car headlights are in the 1,000-lumen range, but much less blinding than the typical bike headlight, because car headlight beam patterns are strictly regulated to keep the high-intensity part of the beam aimed down at the road, not up in the eyes of oncoming traffic.

Some bicycle headlights have reasonable beam patterns, but most use cheap round flashlight-style reflectors that throw at least half the light places it isn't useful.

Of course, helmet lights point the light where you're looking, so it's a bad idea to put a dazzlingly-powerful light on a helmet. But you don't need that bright a light to be seen by motorists. Put the powerful light on the bike where you can control its beam responsibly, and put a smaller light on the helmet for conspicuity.