A method for adjusting brightness of an electronic visual display of an electronic device, comprising: identifying a luminance-indicating area in a field of view of an image sensor of the electronic device; capturing at least one first image of the field of view by the image sensor; determining an ambient luminance value for the electronic visual display using the luminance-indicating area of the at least one first image; and adjusting the brightness of the electronic visual display according to the determined ambient luminance value; wherein the step of identifying the luminance-indicating area in the field of view of the image sensor comprises: capturing a plurality of second images of the field of view by the image sensor, each second image being taken at a different time of a day, and analyzing the plurality of second images so as to identify an area of the field of view of the image sensor which has the most stable average luminance level.