A display device is applied to a light sensing system. The display device includes a display module and a pattern layer. The pattern layer is made of optical material capable of either fully or partially reflecting or absorbing invisible light of specific wavelength emitted from the display module, and is formatted on the display module, thus defining gaps through which invisible light can pass. A light sensor is utilized to sense the pre-determined pattern defined by the invisible light passing through the pattern layer. Based on the light sensing result, the light sensor can recognize the corresponding pattern. The optical material of the pattern layer may be arranged to incorporate locational varying invisible light transmittance to define the pre-determined pattern at a finer degree, thus further increasing sensing accuracy.