A sensing apparatus for detecting light of first and second fluorescent wavelength bands has a light source to generate an excitation wavelength to a first collimator element. A dichroic multiplexer has a first coated surface oblique to the optical axis and treated to transmit the excitation wavelength and to reflect the second fluorescent wavelength band and a second coated surface treated to transmit the excitation wavelength and the second fluorescent wavelength band and to reflect the first fluorescent wavelength band. A focusing element focuses the excitation light toward a light guide and directs collimated light of the first and second fluorescent wavelength bands from the light guide to the dichroic multiplexer. A first detector element is in the path of reflected light of the first fluorescent wavelength band and a second detector element is in the path of reflected light of the second fluorescent wavelength band.
