Abstract: Apparatus for bandpass photon detection containing a lens for collimating input light, a bandpass filter element, and a photomultiplier detector. Light passes from a source into the lens which collimates the light which then is incident upon the filter. The filter is tuned to a particular band of wavelengths, such that out of all of the wavelengths that are incident upon the front side of the filter, a wavelength band is propagated through the filter and passes from the filter to the photomultiplier detector, such that the output of the photomultiplier detector is a voltage level representing the energy content within that wavelength band. In various alternative embodiments, the bandpass photon detectors are arranged in a number of cascade arrangements such that multiple wavelength bands are simultaneously detected.