The best fishing for big bluegill that I've found using lights is under the "buggy whips" or bug attractants that knock bugs into the water. Basically a light turns on at dark, that has a rotating monofilament whip that spins about. Usually for about one to two hours after dark the bluegill will cruise the areas of the bug light waiting for hapless insects to be knocked in. The theory goes that the bug "zappers" aren't as good because the bluegill don't like the taste of electrified or cooked bug as well. I don't know how true that is, but it makes some sense.
I'm not sure if this is what you're talking about, but I realize that there are lights that are used to attract white bass, because (I think) they attract zooplankton, and consequently smaller baitfish, thus starting the food chain.
I've used two lights submerged at each end of the boat to attract alewife, in turn atrracting Wiper and Walleye. There are clouds of zooplankton around the lights after just an hour. I don't see why it wouldn't work for gills.
...and crappie as well. One interesting theory I've heard is that summertime fishing for bluegill in smaller ponds is really poor because virtually all of the oxygen comes from photosynthesis (as opposed to wave action) and when plants begin to respire at night that the dissolved oxygen levels start to drop and bluegill get really inactive.
I've fished the docks at Lake Perris at night, using an underwater lamp (Just attach it to a battery).... Like Bruce said it starts the food chain.
Brings in lots of tiny freshwater shrimp and then minnows and such... the problem is... I love to catch Bluegill and when I fished with the light... you really didn't know what you were going to catch.... Bass... Trout... Crappie etc... We have monster Largemouth at Perris (lake record is over 19 lbs) and fish that size will keep the bluegills away. Our Bluegills grow large to up to 3 lbs plus, but the mouth on a big Bass is like a bucket and will scare all but the mightiest bluegill away.
One thing I did try a few years back was the little light sticks. They are about an 1 1/2 inches long. You shake em up and then bend them till you hear a crack, the chemicals inside mix and the little green light comes on and will stay on for about 24 hours.
I fished this about 9 inches ahead of the hook. I tried them at night and even during the day and they caught fish when other anglers were struggling to get a bite. I have since heard rumors that they are illegal in some states so don't use them without making inquiries. But take it from me... when the fishing slows down they can make a huge difference.
If you decide to try these, (you can get them at Cabelas I think) here's a trick.
They come with small soft plastic sleeves. You can use these sleeves to attach them to your line. Prior to tying on your hook/jig slide the sleeve onto your line, place it about 9 inches above where you anticipate your bait to be and hold it in place with a tiny piece of shot or a slip knot and bead. This way your sleeve is in position and when you need the light just crack it and apply a little saliva and slide the light into the sleeve. Good to go.
I also use these for night float fishing. They work really well and you can see them from a long ways off. Remember you don't need too much light showing. Once you cast out the light creates a reflection so if you have a one inch light stick you'll actually see about 2 - 3 inches of light because of the reflection. Makes your heart pound when you look out into the darkness and all you see is black... set the hook...
Sounds good for me to try it at my parents live on private lake. I think it would be great for crappies because lights to bring lot of minnows closer then crappies move in! Insects would work when the light is above the water and maybe only 2 feet above the surface.
About 10 years ago, my wife and I spent several days in the Key West in Florida. We drank some beer at night on a private dock with lights in the water. We watched lot of baitfish and small fishes all over the dock with light on and several big tarpons swim around. Of course no fishing but interesting to watch it at night with lights. During the day..... no fish!