Somewhat related...

I had a bit of a strange incident a few days ago. A guy had two lights, somewhat bright, maybe 2 or 300 lumen, mounted far apart on his wide, flat bars. I glanced up, and was certain...I mean, dead certain that it was a car, quite far away. The position of the lights, the height, and the brightness was all consistent.

When I saw that he was in fact a cyclist I was stunned. How many people have thought the same and pulled out in front of him, secure in the knowledge that they had tons of room between them and this oncoming 'car'?

I think that a single, bright, steady headlight centrally mounted is the best choice for a cyclist. The driver can see you, judge your distance and identify you immediately.