It is difficult to find the old fashioned rear light. When I used one, I eventually kept the power supply independent of the front lights. A 1 watt bulb was useless in penetrating the red lens. A 3 watt bulb offered a good degree of illumination. Far better than an LED flasher by itself.
Reflectors work great at the back of the bicycle.
I use a three inch amber reflector on the fender and it works great. I'm sure it is the first thing a motorist will see on a flat level section. For illumination, I used a Xenon strobe. It is much less directional than LED and brighter too. More expensive and the batteries last only two winter commutes.