A very bright helmet mounted light had done more to increase passing space and decrease passing speed than anything else, when riding at night. I use a 1200 lumen Zebralight H600w Mk IV, with the temperature controlled brightness it is probably closer to 900 lumens sustained but still it works great. Blinding motorists is an issue created in the minds of Bikeforums posters.

You can use primary (non-rechargeable) CR123A lithium batteries and set the strobe level to 502 lumsn for that model of Zebralight. Runtime is impacted but the brightness should stay the same.