Abstract: A low cost means for increasing measurement sensitivity in LED near-infrared instruments is disclosed which utilizes a current modification means for modifying the driving current supplied to each IRED as a function of the opacity of the particular sample being measured. The current modification means is part of the processing means and comprises means for measuring a signal level for each IRED at an analog-to-digital converter. Based upon the signal level detected for each IRED, the current modification means modifies the current to each IRED to a value that is as high as possible without saturating the analog-to-digital converter. Thus, by modifying the driving current of each IRED to such a maximal value, the analytical instrument of the present invention provides high resolution without the use of expensive electronic circuitry. Also provided is a system for generating and storing an optical signature of a particular user, thus further insuring the accuracy of measurements taken by the instrument.