Just stumbled across another option.

Not so high tech, not so visible, and again rear brake only (well you could have them on your front brakes, but it probably wouldn't do much good)

Promax I-Pad's Brake pads with integrated rear facing (3mm?) red LED's (one per pad).

If they gave these amber side LED's as well they might be better.

V-Brake/Canti's only I think.