  A fluorescence system is developed by using several light emitting diodes
(LEDs) with different wavelengths as excitation light sources. The fluorescence
detection head consists of multi LED light sources and a multimode fiber for
fluorescence collection, where the LEDs and the corresponding filters can be
easily chosen to get appropriate excitation wavelengths for different
applications. By analyzing fluorescence spectra with the principal component
analysis method, the system is utilized in the classification of four types of
green tea beverages and two types of black tea beverages. Qualities of the Xihu
Longjing tea leaves of different grades, as well as the corresponding liquid
tea samples, are studied to further investigate the ability and application of
the system in the evaluation of classification/quality of tea and other foods.
