I have a dock on a local lake and was considering installing the green underwater lights.
Do they actually work attracting crappie?
I know my above the water lights work but the bugs are awful if they work as well I want the.

I can't say for crappie but I sure catch a bunch of sandies off of them. There are a couple of docks I fish that have crappie structure under the dock with the lights but I've never fished for them. But may try next time out if I can keep the sandies off my jig.

Mine attracted tons of threadfin shad, that said the easiest thing to catch off of my dock is bass. Crappie will be there sometimes, but the numbers of bass & gar are the most prevalent.

It attracts the night time bass fisherman too!

they work great for attracting crappie, especially if you put structure down (christmas trees or bamboo, etc.). Caught many, many crappie under lights on docks - plus lots of summer sandies, bass and occasional catfish.

Lights attract plankton which in turns draw in bait fish which in turn draw in predator fish which usually hang on the outside of the light ball and ambush the bait as it swims around in circles around the light. You have to have lots of bait to start a feeding frenzy. A little bit of bait and you will have fewer fish there but they will be there.
Crappie and bass and catfish hang close to the lights and eat the bait. If you have crappie in your lake then you will have crappie around the light for sure but again it all depends on the bait being present.

I catch them occasionally at PK under lights. They won't actually come into the light like stripers and sandies do but will be attracted to the large amount of minnows. I usually catch them right at the edge of the light. Considering the size of the of the stripers and LM Bass I've seen under the light, I don't blame them for not wanting to be illumiated as a target.

I have one (took the 2nd one off) on my boat and the few times I used them they worked pretty well.

I have an underwater green light. It works. It generally takes around an hour to attract the fish after the lights are turned on unless you have structure to keep them.

Bass will come into the circle of light. Crappie will not. So if you want to catch crappie cast out beyond the light and slowly retrieve your jig toward the edge of the light circle. Floats are good for jig control when you do this.

Create some structure at the outer edge of the light circle for best results.

And yes, boat fishermen will be attracted to your underwater lights and fish your dock area. Not much you can do about that except turn off the lights when you are not fishing yourself if it bothers you.