importance of resonance

According to Steven Gibbs an HDR unit works based on resonance. He also told me that his HDR unit works better with an old Radio Shack inverter than with household power. The current in your house is sine wave. However the old inverters generated a square wave. Basically, a square wave has richer harmonics as you can see in the motor movie. Take a look at the movie. Actually, this is the key - resonance.