A touch screen includes a display screen having an upper surface that provides picture information, and an optical module that emits rays in directions that can be parallel with the upper surface of the screen. When an object, such as a stylus, pen or a finger is placed on the screen to select a portion of the picture information provided on the screen, at least a portion of the rays are reflected off of the object and detected in order to determine a position of the object on the screen. The position of the object can be calculated in various ways including calculating a position of the object based on a phase delay of the reflected rays, or based on an intensity of the reflected rays, or based on an incidence angle of the reflected rays.