Originally Posted by
Giro
As MechBgon suggests, don't depend on just one light. You want to take a variety of steps; also consider a good ANSI Class 2 or 3 reflective vest.
Another tail light to consider is the
Ultrafire WF-501 B. Do note, however, you would have to make the investment in 18650 batteries and charger.
I have this light and even with the cost of batteries and charger, the total is under $30.
It's searing to the eyes -- you will injure your retina looking into it.
It's awesome for fog or for the mornings you ride directly into the sun and you need something to make you stand out (for the drivers with dirty windshields).
Have the SuperFlash too, and I use them both. The Ultrafire is 10x more powerful though.