In some embodiments, a system comprises a head-mounted frame removably coupleable to the user's head； one or more light sources coupled to the head-mounted frame and configured to emit light with at least two different wavelengths toward a target object in an irradiation field of view of the light sources； one or more electromagnetic radiation detectors coupled to the head-mounted member and configured to receive light reflected after encountering the target object； and a controller operatively coupled to the one or more light sources and detectors and configured to determine and display an output indicating the identity or property of the target object as determined by the light properties measured by the detectors in relation to the light properties emitted by the light sources.
