candlepower - light intensity at a distance
lumen - light energy over a volume
http://www.theledlight.com/lumens.html

not so helpful in choosing a light
10-50 lumens give you a "be seen" bike light, or perhaps enough on a bike path
200-2000 lumens give you enough light to see where you are going at 15 mph or faster.
I use a 200 lumen setting on the MS light most of the time, I also have 4 other flashlights available to turn on.

So share the conditions you will ride in, there are plenty of expert around here.