Wet niche light fixtures come with a cord attached. You have to install the j-box close enough to allow the light fixture to be removed from the niche, set up on the pool deck (while unwinding the cord) then open up the fixture to replace the bulb. The cord usally will not reach to a pool house. This is why the pool junction box is located as close as 4 feet from the pool edge and is to be 8" above the max water level.
This allows you to change out the bulbs without draining the pool.
The only service call I know of where you get paid to go swimming.