If you are in a situation where you have to move the power source to your pool light and the light cord will not reach to the new location, you have two options. You could buy a whole new light fixture with a longer cord or you could splice into the existing cord and add to it. If you add a spliced cord, you should not put the splice underground inside the light wire's conduit. That pipe generally collects water and the spice would eventually short out. The splice should be made above ground. This guide shows you how to splice into your exiting light cable above ground.