I have used the floating lights and submersable lights for a few years now. I havent noticed much change in my catch but they help with knots etc. I also have used 12v submersable bulbs from a landscape lighting store attached to wires and a batt. They are also ment for ponds. They are super cheep and are the brightest ive used.

Where are you using them at and what are you using them for? Cause I can go drop a jig in a brushpile in the dark and let it soak for an hour and get nothing. Then I can drop a light down there and have the bite turn on like... well, a lightswitch.
Lights won't help you unless a) the fish are there already, or b)you have the same light in the same place night after night after night so it becomes part of the fishs' enviorment.