  We report on the development of a compact commercial instrument for measuring
carotenoids in skin tissue. The instrument uses two light emitting diodes
(LEDs) for dual-wavelength excitation and four photomultiplier tubes for
multichannel detection. Bandpass filters are used to select the excitation and
detection wavelengths. The f/1.3 optical system has high optical throughput and
single photon sensitivity, both of which are crucial in LED-based Raman
measurements. We employ a signal processing technique that compensates for
detector drift and error. The sensitivity and reproducibility of the LED Raman
instrument compares favorably to laser-based Raman spectrometers. This compact,
portable instrument is used for non-invasive measurement of carotenoid
molecules in human skin with a repeatability better than 10%.
