Look, one of these things....
http://www.ebay.co.uk/itm/Microwave-Switch-Occupancy-Sensor-360-degree-Light-Presence-Detection-/230851297808?pt=UK_Light_Fittings&hash=item35bfcf4210
What I want to happen , is when someone walks in the door, the 2 wall lights come on , and the extractor /...