A method of detecting an occupancy state of a living space for controlling the on/off performance of a lighting apparatus. The method using a microwave motion sensor to detect a motion intrusion, wherein a microcontroller with program codes analyzes a time duration and a frequency pattern of the echoed microwave signal generated by the motion intrusion in the living space. The method using an occupancy counting APP to record, wherein an updated numerical value represents the number of occupants remaining in the living space for operating the illumination. The echoed microwave signal is judged with the frequency pattern being lower or higher than the frequency pattern of the microwave signal transmitted to adjust the numerical value. When the microwave motion sensor is operated with a frequency level below 20 GHz, a microwave confining device is required to limit a detecting capacity of the microwave motion sensor.