A method is provided of compensating for stray light in a light sensor having a detection photosensor (7) and a reference photosensor (20), the reference photosensor (7) being for use in compensating for stray light falling on the detection photosensor (20). The method comprises using the reference photosensor (20) at least in part to determine a bias voltage applied to the detection photosensor (7). Based on this method, a display device is provided comprising a backlight and a light sensor for determining an ambient light level with the effects of stray light from the backlight substantially removed, with means provided for controlling the intensity of the backlight in dependence upon the determined ambient light level.