Lights should be positioned as far apart as possible. The further two points of light are away from each other, the further away the eye can distinguish them. Separating lights vertically also ensures that you will be seen by people in low and tall vehicles alike. For headlights a good setup is to have a primary handlebar mounted headlight, and a secondary light on the helmet. Good helmet lights should have a narrow beam and not be too bright – you want to be able to light up a specific area where you’re looking without blinding everyone around you.
For taillights, a rack or seatpost mounted light in addition to a helmet light provides good coverage.
