A light sensor and a sensing method thereof are provided. The light sensor includes a plurality of sensing sub-pixels and a control circuit. The sensing sub-pixels are arranged in an array to form a sensing array. The control circuit is coupled to the sensing sub-pixels. The control circuit operates a plurality of diodes of the sensing sub-pixels in a photodiode mode to sense intensity of ambient light. The control circuit operates the diodes in a Geiger mode or in an avalanche linear mode according to the intensity of the ambient light.