There is not much information on how this light works on the site. It isn't easy to tell from the picture. This works off of induction (magnets) and is incredible! You put one half of this on the outside of the pool and stick the light on the inside. When the two halfs connect via the magnets the light comes on. This light works perfectly below the surface of the water without modifying the pool at all. I have this in a 16' pool and there is plenty of light.