interesting idea, but not really what I'm looking for. those only hold 22 lbs and for a larger light I don't think that would be enough.
I was thinking more like.... your light has two or 4 holes for attaching on both ends so you run the cbles out of the attachment points to a single cable over the center of the fixture and that cable runs through an eyelet and down to the wall where you have a small crank that can stop each time you turn it. like a winch pully for getting your boat on the trailer. and then when you're done you just take the pressure off the system by turning the crank a bit past the stop and push in the stop and slowly crank it backwards back down to the tank.
For alot of people this may be ugly, but the back of my tank is in its own compartment in the wall, so ugly is not a concern