The SP discussion brings up something i'ven been ruminating on for a while: I want to be seen but i don't want to blind or disorient the woman coming up behind me in the 6000lb suv with an uber-bright light. Somthing called "target fixation" happens when you see something you don't recognize or which disorients you: you inadvertantly fixate on it and tend to head towards it.
Target fixation is a well-known phenomena especially among newbie motorcyclists - lots of head-on collisions happen around curves where the newbie drifts into the car heading their way.
Cyclists tend to run into rocks/roots/etc by fixating on the obstacle. you know it's true...
I want the person behind me to see 1) see me, 2) avoid me. I think this is best done with standard blinkies and good reflector tape, so the person behind you can judge what you are, how far away, how big, etc...