In a display apparatus, a display panel is divided into dimming areas and a backlight device includes light source blocks providing light to the dimming areas. Average gray-scale values and maximum gray-scale values respectively corresponding to the dimming areas are generated based on image signals provided to the dimming areas. Whether the average gray-scale values and the maximum gray-scale values are respectively within first and second reference ranges are checked. One of at least two parameters is selected according to a checked result, and representative brightness values respectively corresponding to the dimming areas are determined using the selected parameter. Duty ratios of the light source blocks are controlled based on the representative brightness values. As a result, power consumption is reduced when applying a dimming device to the display apparatus.