A hand-held portable modular spectrometer unit. The unit includes a detachable head containing a light source and optical components for detecting spectral information from light reflected from or transmitted through a target and a processor for converting the detected spectral information into digital information. The unit also includes a plug-in rechargeable power supply and a control module for controlling the components in the measurement head. The controller includes a computer processor for analyzing the digital information produced by the measurement head and a display monitor for displaying spectral information produced by the control unit. In preferred embodiments several measuring heads are available. Each of these measurement heads includes a spectrometer.