A legacy-type fluorescent lamp fixture involves a magnetic ballast and a starter unit socket. Power savings are realized by using a retrofit fluorescent lamp assembly in place of the fluorescent lamp that would ordinarily by held in the fixture. The retrofit assembly may, for example, have a smaller fluorescent lamp. A digitally controlled electronic ballast within the retrofit assembly drives the smaller fluorescent lamp efficiently, thereby achieving power savings. In addition, an RF-enabled switch is installed in the starter unit socket. The RF-enabled switch communicates multi-bit digital control signals in serial fashion from the starter socket, through existing wires of the fixture, through the lamp holders of the fixture, and into the retrofit assembly. The electronic ballast receives these signals, decodes them, and in response turns on or turns off its lamp as commanded. Additional power savings are thereby achieved by keeping the lamp off when it is not needed.