The point Barry is making is that we try to help people to solve problems themselves by tutoring them. What we specifically do not do is produce end products for them. If we went down that route we would become a free design team and line peoples pockets at our expense.
What you propose is already done in hundreds of commercial products, for example, water faucets (taps) that flow when hands are placed under them and illuminated mirrors that are activated by waving at them. The principle is simple, an IR source points outwards, an IR sensor points outwards but placed so it cannot see the source directly. An object placed where they can both see it reflects light back and the output from the sensor and triggers a monostable. The monostable is a one-shot timer with it's output controlling the AC. It keeps the AC active during reflection time and for a pre-set time afterwards then turns it off until triggered again. It's very easy to do.
There is a catch though - how do you make it ONLY respond to a reflection from it's own source and not from other IR devices? The answer depends upon where it is going to be used, have a think about it.
Brian.