A display device is provided, which can precisely control a light source by measuring the quantity of light from the light source under uniform conditions. The display device includes a display panel displaying an image, a light source generating light, a light guide plate guiding and providing the light to the display panel, a receptacle accommodating the light source and the light guide plate, an optical sensor fixed to the receptacle to sense the light, a light receiving hole formed at an edge of the receptacle to provide a path through which the light reaches the optical sensor, and an optical adjustment member interposed between the light guide plate and the optical sensor to reduce luminance of the light incident to the optical sensor. The optical sensor is completely exposed to the optical adjustment member through the light receiving hole.