Apparatus is provided to sense and measure solar-induced luminescence, as well as reflectance, within the field of view of a target window for receiving a composite ray of light from the target. A first filter within the path of the composite ray of light transmits a first narrowband component thereof,...http://www.google.se/patents/US4865424?utm_source=gb-gplus-sharePatent US4865424 - Optical device with adjusting means
