Back in the day, I used to use em off the side of the boat. Its not a guarantee, but it does work. I gets the food chain going. The zooplankton are attracted to the light, the minnows are attracted to the smorgasbord and in turn so are the predator fish. You usually will do best fishing the edge or outside the edge of the visible light. Like I said, its not a sure thing. I've watched crappies feed on the minnow under the green light, but I couldn't buy a single bite.
I went out on a casino boat in Key Largo many moons ago and they anchored up out in international waters and had bright white lights out around the boat. By the end of the night or at least the end of my gambling budget I went to the rail to find the entertainment of the evening. The light had attracted bait fish and sharks were surrounding the boat pickin of mullet or whatever they were like candy. I was awesome.
