Don't know if this helps any, but, Petco sells a kit with an AC
adapter which hangs on the back or side of tank and comes with two LEDs (Blue & Green) which are completely submersible. You can run the wires inside the tank and use suction cups to mount LEDs on glass, or partially bury in sand, or place behind rock, etc. They are sort of spot light LEDs. Below is two I have in my 29gal and they shine a reasonable distance. Think kit is around $19.95.
Personally, I think they're kind of groovy! (Did I just say groovy? Must be showing my age!)
I think are good for both freshwater and saltwater, but am not positive.
Hope helped, somewhat.