A method of visually measuring the brightness of ambient lighting around a display device is disclosed. In this method, first, a reference brightness of the display device is determined according to a type of display device. Thereafter, information about locations where the display device is used is received from the user, and illuminance values of the display device corresponding to brightness stages are set based on the reference brightness and the location information. Then, a reference brightness is converted into each of the illuminance values corresponding to each of the brightness stages. The converted images with the illumination values corresponding to the brightness stages are displayed to the user, and an image that has a brightness value nearest to the brightness of ambient lighting is selected, and the brightness value of the selected image is determined as the brightness of ambient lighting.