Abstract: A spectral densitometer system reads dosimeter cards. The cards contain bar codes with information for calibration of the system and for identification of the cards (serial numbers for each card). The densitometer has compartments optically and physically separated by a mechanism which contains a slide for receiving the cards and moving them into alignment with openings which expose the bar code to a bar code scanner in one of the compartments. The compartment containing the scanner also contains a source of illumination which projects through another opening and through a radiation sensitive patch. A scanning spectrophotometer in the other compartment reads the spectrum of the transmitted illumination. The system includes a computer, which may be a separate host computer, connected to the spectrophotometer and the bar code reader via communication ports. The computer computes the dosage based upon the wavelength measurements and the calibration information contained in the bar code.