an object such as the hand 2 in the xy plane is determined by object detection by said three transceivers 5 said position is determined by sequentially transmitting an acoustic pulse from one transceiver 5 at a time each of the three transceivers 5 determines if a reflected signal is received after each pulse is sent by one of said transceivers 5 the object position determined by this sequential transmitting and parallel receiving method is translated into a binary code from this code the xy position of the object is determined and is translated into light control instructions like light beam deviation or other light controls like colour intensity focus etcetera in fig1 a time diagram is given of the proposed method the three transceivers subsequently send acoustic signals on three time intervals t 0 t 1 and t 2 the three transceivers will determine if an echo signal sent by a transmitter is received which depends on the position of the hand 2 in fig1 a dotted block indicates that the received echo signal strength is below a predetermined threshold and the echo signal is given value 0 if the echo signal strength is equal to or above said threshold the echo signal is given the value 1 this echo information is represented in table 1 the x and y value determine the actual position of the hand 2 in the xy plane if the hand 2 is moving to a certain direction the x y values change from these values the hand displacement direction.