To disconnect a light, you must disconnect all three wires of the fixture, including the black hot wire, the white neutral wire, and the yellow or copper ground wire. The wires coming from the light fixture and the wires coming from the junction box are connected with plastic wire nuts.
Flip the breaker or remove the fuse that supplies power to the light fixture before touching the wires. Unscrew the wire nuts by hand. Disconnect the ground wire, which may be wrapped around the mounting bracket or fastened in place with a green screw. Carefully separate the wires of the fixture from the wires of the junction box.