A touch screen includes light emitters and light detectors arranged around a periphery thereof. The position, orientation, shape and/or size of objects may be determined by switching the light emitters on one-by-one and detecting shadows caused by the objects. The objects include at least a first part with optical properties of a first type and a second part with optical properties of a second different type. By determining the optical phenomena caused by the second part, the orientation of the objects may be determined and/or the objects may be recognized or identified.