An optical system comprises a wearable device for measuring one or more physiological parameters. The physiological parameters may change in response to stretching of the hand or movement of fingers or thumb of the user, or the parameters may be related to blood constituents or blood flow. The wearable device comprises a light source with a plurality of semiconductor diodes and a detection system that measures reflected light from tissue comprising skin. The semiconductor diodes may be light emitting diodes or laser diodes. The signal to noise ratio for the output signal may be improved by synchronizing the detection system to the light source, increasing light intensity of at least one of the plurality of semiconductor diodes from an initial light intensity, and using change detection that compares light on versus light off for the detection system output. The wearable device is also configured to identify an object.