If you're mixing it up with traffic, you need:
-- a front light to see at your speed. I chose 20w spot so would not have to drop speed much
-- a front light to be seen. I chose a 10w flood. [ part of 2 light set ]
-- front side lights so cars don't turn into you
-- a rear light.
The first three are most important. Only about 2 percent of accidents are strikes from rear. Most are from the side, and some from the front.