A touch screen, including a layer of light-transmissive material having an upper surface that is exposed for touch by one or more objects, a plurality of light emitters underneath the upper surface, a first lens assembly for directing light beams emitted by the light emitters into the layer at an angle such that the light beams, when entering the layer, remain confined to the layer by total internal reflection when the light beams are not absorbed by any of the objects touching the upper surface, a plurality of light detectors for detecting light beams and for generating outputs indicating the amounts of light detected, a second lens assembly for directing light beams at a surface of the layer towards the light detectors, and a calculating unit for determining respective one or more locations of the one or more objects touching the upper surface, based on outputs of the light detectors.