A programmable underwater lighting system, comprising: an underwater lighting fixture (16a-16d, 18a-18d) for installation in a pool or spa, the underwater lighting fixture including a light source, a microprocessor in electrical communication with the light source, and a memory having at least one stored control program executable by the microprocessor for controlling the light source, an alternating current power supply for supplying electrical power to the underwater lighting fixture, a logic power supply for supplying electrical power to the microprocessor, and a Power Line Carrier communications subsystem connected between the AC power supply and the logic power supply, and in electrical communication with the AC power supply, the logic power supply, and the microprocessor, and a central controller remote from and in communication with the underwater lighting fixture, the central controller allowing a user to specify a desired lighting sequence and transmitting an instruction to the underwater lighting fixture over a power line interconnecting the central controller and the underwater lighting fixture to selectively execute the stored control program to produce the desired lighting sequence, wherein the underwater lighting fixture receives the instruction from the central controller via the AC power supply using the Power Line Carrier communications subsystem and executes the instruction, and wherein, prior to transmitting the instruction to the underwater lighting fixture the central controller authenticates the lighting fixture by communicating with the lighting fixture and determining whether the lighting fixture is authorized for use with the central controller. an underwater lighting fixture (16a-16d, 18a-18d) for installation in a pool or spa, the underwater lighting fixture including a light source, a microprocessor in electrical communication with the light source, and a memory having at least one stored control program executable by the microprocessor for controlling the light source, an alternating current power supply for supplying electrical power to the underwater lighting fixture, a logic power supply for supplying electrical power to the microprocessor, and a Power Line Carrier communications subsystem connected between the AC power supply and the logic power supply, and in electrical communication with the AC power supply, the logic power supply, and the microprocessor, and a central controller remote from and in communication with the underwater lighting fixture, the central controller allowing a user to specify a desired lighting sequence and transmitting an instruction to the underwater lighting fixture over a power line interconnecting the central controller and the underwater lighting fixture to selectively execute the stored control program to produce the desired lighting sequence, wherein the underwater lighting fixture receives the instruction from the central controller via the AC power supply using the Power Line Carrier communications subsystem and executes the instruction, and wherein, prior to transmitting the instruction to the underwater lighting fixture the central controller authenticates the lighting fixture by communicating with the lighting fixture and determining whether the lighting fixture is authorized for use with the central controller.