Method of visually measuring brightness of ambient lighting around display device

A method of visually measuring a brightness of ambient lighting surrounding a display device, the method comprising:

• selecting a type of display device as either a self luminescent display-type device or a reflective or transmissive display-type device;
• displaying a plurality of gray patterns that overlap one another;
• determining the reference brightness of the display device by determining an optimal gray scale reproduction state of the display device according to whether the gray patterns are visually distinguished from one another;
• selecting a location of the display device from at least one predetermined location corresponding with the determined reference brightness;
• displaying at least one brightness stage from a plurality of brightness stages for a user to select according to the determined reference brightness and the selected location such that a converted image having an illuminance value corresponding to the selected brightness stage is displayed;
• and
• comparing the illuminance value of the displayed image with the brightness of the ambient lighting and selecting the brightness stage corresponding to an image having a brightness value nearest to the brightness of the ambient lighting,
• wherein the optimal gray scale reproduction state of the display device is determined depending on the type of display device, such that a white level of the reference brightness is adjusted and set for the reflective or transmissive display-type device, and a black level of the reference brightness is adjusted and set for the self luminescent display-type device.