I think you're talking about winterizing. It really depends on the type of light and how deep it was put in the pool. Most of the time, if it's closer to the top of the water, you'll "sink" it by unscrewing it and tying a weight (jug with rocks works well) to it. It's still be attached via electrical wire.
Properly mounted and installed lighting in an inground pool should not be a source of extraneous light transmission to any place other than the below the level the surface level of the water. The water surface may reflect or transmit a glow as a result of the light reflectivity, but should not come out.