The invention provides a lighting controller, comprising: a detector adapted to detect a voltage of a power source, said power source is for providing power to a lighting unit via a lighting driver; a controlling unit, coupled to the lighting driver and adapted for controlling the driver to deliver a constant power to the lighting unit regardless of the power source is being consumed, before the detected voltage drops below a first threshold, and controlling the driver to deliver a gradually reduced power to the lighting unit after the detected voltage drops below the first threshold. Wherein the controlling unit is further adapted for switching an up-converter between the power source and the driver to boost the output voltage from the power source to the driver, in a first condition; and bypassing said up-converter, in a second condition, and implementing said step of controlling the driver; wherein said first condition comprises operating in high occupancy periods, and said second condition comprises operating in low occupancy period.