If you ride with two lights, make sure they are not attached side by side. From the perspective of oncoming traffic, they look like headlights from a distant car. When I went to a local bike skills class, the instructor told the story of a car making a left turn directly in front of an oncoming bicycle, almost hitting him. The driver pulled over immediately when she realized her mistake and apologized; to her the dual headlights positioned horizontally on the handlebars looked like an oncoming car that was a good block away.

Positioning the dual lights one on top of the other instead.