In one form, a touch screen includes an optically transmissive medium, first and second light sources, a detection circuit, and a control circuit. The first light source is positioned to emit light across the optically transmissive medium in a first direction, and the second light source is positioned to emit light across the optically transmissive medium in a second direction orthogonal to the first direction. The detection circuit detects standing wave patterns of light emitted by the first and second light sources along the first and second directions. The control circuit is coupled to the detection circuit and measures a first standing wave pattern in an untouched condition, and a second standing wave pattern in a touched condition. The control circuit detects a touch location in response to a difference between the first standing wave pattern and the second standing wave pattern.