A display device includes a display panel including a plurality of pixels, an illuminance sensor to measure illuminance, and a display controller which includes a processor a brightness controllers. The processor calculates an external illuminance value with reference to a signal from the illuminance sensor. The brightness controller turns off at least one of the pixels and controls the brightness of the display panel when the calculated external illuminance value is in a first region. The first region may be, for example, in a mesopic region.