A light sensing method, applied to a light sensing system comprising a light sensor and at least one light source. The light sensor comprises a plurality of light sensing units. The light sensing method comprises: controlling the light sensor to capture images according to the light source; generating an exposure condition according brightness that each of the light sensing units senses, to control all the light sensing units to generate a target brightness distribution according to the exposure condition; and controlling the light sensing units to sense light from the light source according to the exposure condition. The light sensing system can have a better SNR via adjusting the exposure condition for each one of the light sensing units. Such light sensing method can be applied to compute physiological parameters.