Optical radiator coating sensor

A detector for measuring the reflectivity of a pollution reduction coating, comprising:

• a housing;
• a substantially transparent window formed in the housing;
• a light source operationally connected in the housing and adapted to shine out the window onto the coating;
• and
• a photodetector assembly operationally connected in the housing and further comprising:
• a first photodetector positioned to receive light from the light source reflected by the coating;
• a second photodetector positioned to receive light from the light source reflected only from the window;
• and
• a third photodetector positioned to receive light directly from the light source;
• wherein the first and second photodetectors are substantially blocked from receiving light directly from the light source;
• wherein the second photodetector is substantially blocked from receiving light from the light source reflected by the coating;
• wherein the third photodetector is substantially blocked from receiving light from the light source reflected by the window;
• and
• wherein the third photodetector is substantially blocked from receiving light from the light source reflected by the coating.

A method for measuring the degradation of a coating using a detector having a light source and a plurality of photodetectors in a partially transparent sensor housing, comprising the steps of:

• aa) measuring reflected light reflected from the coating as a function of time;
• bb) compensating for changes in intensity of the light source over time;
• cc) compensating for changes in the transparency of the housing over time;
• and
• dd) calculating the reflectivity of the coating as a function of time.