The helicopter flight instructor reported that he was training a new company pilot at night, and they were using night vision goggles. He added that, while in a hover, he attempted to demonstrate the use of the controllable search light to the pilot in the right seat. The flight instructor added that, "to adjust the light, I took the [left] cyclic in my left hand which would normally be holding the left collective and attempted to reach the control switch for the light and grabbed the throttles of the right collective with my right hand. My right hand would normally be on the left cyclic." He further added that he then inadvertently pushed down on the collective, and the helicopter began to settle on the runway. He reported that in response "[his] reflex was to pull up with [his] left hand (which would normally be on the collective)," and when he did so the helicopter moved rearward. Subsequently, he "pushed the cyclic forward to correct" the rearward movement, but in doing so, the helicopter touched down hard, and the main rotor impacted the upper wire strike protection unit. The main rotor sustained substantial damage. The flight instructor reported that there were no preaccident mechanical malfunctions or failures with the helicopter that would have precluded normal operation.