quantum theory fluorescence is linked to a process in the atom which only occurs when the atom under consideration takes in a definite quantity of energy if the emitted fluorescent light has the frequency u03bd a c u03bb a c velocity of light this energy must be at least be h u03bd a h planck 39 s active quantum if the light irradiated has the wave length u03bb a it can only introduce the energy h u03bb e into the individual atom since this is the magnitude of the quanta out of which the energy of the light of that frequency is composed hence fluorescence can only occur when h u03bd e gt h u03bd a or when u03bd e gt u03bd a and u03bb e lt u03bb a referring next to fig2 a system in accordance with the present invention can be better appreciated the pieces of glass of types 103 and 105 rest on carrier 221 which may for the present example be understood to be a conveyor belt at an appropriate point on the path of the conveyor 221 the glass pieces 103 and 105 are illuminated by uv lamps 215 the glass pieces 103 fluoresce and that fluorescent emission is detected by optical sensor 207 which may for example be one or more cameras or one or more optical sensors and may for example be arranged in an array extending across all or a portion of the carrier 221 for.