A sensing device is provided to sense light and generates a sensing output signal indicating intensity of the light. The sensing device includes a photo element, a comparison circuit, and a logic circuit. The photo element senses the light and generates a current signal at a first node. The comparison circuit is coupled to the first node and receives the current signal. The comparison circuit includes a filter for filtering a high-frequency component on the current signal, and the comparison circuit generates a result signal according to the filtered current signal. The logic circuit receives the result signal and performs a logic operation to the result signal to generate the sensing output signal.