Have no idea what that is, lol! Something involving light and water it sounds like... I know what candling is and what floating is but haven't heard of the two being combined. Is that just a misnomer, perhaps? Water testing is pretty unreliable overall, a strong torch is best in my experience.
I see. Well, it's nowhere near as reliable as torching/candling. (Who actually uses candles for that anymore? lol).
Eggs float both when they're so rotten they're about to explode, and when they're almost ready to hatch. Some rotten eggs won't float apparently; also there are numerous degrees of floating or buoyant behavior which can mean varying things, from stage of development to stage of decomposition, and also be influenced by things like what sort of bacteria invaded and killed the embryo, what degree of heat the egg was exposed to as it rotted, etc.
Anyway, that's my 2 cent's worth, torching is best, but maybe someone has some more useful info.
Water candling is when you place the egg in water and watch for the egg to move once the water is settled. Most people use it right before lock down. There are a lot of youtube video's on it showing what you should see. If you do try this make sure the chick has not pipped yet or the chick will drown as water pours in through the pip spot.
I don't think that water candling should be used to verify/confirm whether a chick is dead in the shell however it can be used to say that yes a chick is moving in the egg because that movement is what makes the egg move in the water. I wouldn't use it to eliminate/throw out eggs because the chick could be napping when you do this and so they would not be moving.