There used to be available little "diode discs" that were placed at the bottom of an incandescent light socket. The rectified voltage that was fed to the light averaged only half of normal and reduced energy used. But the lights were a very dim-orange colour and flickered. Since the filiament was cooler, it had less resistance so didn't save as much energy as hoped for. If the light gives 90 percent heat and 10 percent light at full voltage, then maybe it gives 68 percent heat and only 2 percent light at half voltage.
Since refrigerators have a powerful motor that consumes power day and night, some people have connected their 'frig to a "power factor controller". Apparently, the poor power factor of the motor makes the utility's power meter record much more power than is true. They say that the power factor controller makes a big reduction on their electricity bill.