This disclosure relates to a method of detecting an occupancy state of a living space for controlling lighting apparatus. The method comprises using a motion sensor to send wave signal and detect echoed signal reflected from a moving human body and using a control circuitry operated with a software program to analyze the echoed signal for establishing a numerical value account. In referring to preset parameters, the software program judges the echoed signal by analyzing time duration and frequency pattern of the echoed signal as an incoming motion, an outgoing motion or a local random motion, such that the numerical value account is accordingly updated to represent actual occupant number for activating the controller circuitry to turn on or turn off the lighting apparatus.