Stray Light Measurement With Solid State Light Luminaire In A C-Type Goniophotometer With Rotating Mirror

The present work has been done to quantify the stray light on a C-type goniophotometer with rotating mirror in the test of a solid state light luminaire. We used two methods: blocking the light beam with black screens and collimation of the light beam with small aperture diaphragms (millimetre). The goniophotometer is inside of a completely dark room with large aperture diaphragms (C-type); however, there are reflections of light on the walls and floor due to the surface characteristics and painting. The screens with millimetre diameters and the diaphragms were placed at a distance of 10 cm from the detector to avoid further reflections. By using screens, the light reflections can be directly measured because the light beam that is aligned with the photometric centre is locked. By using diaphragms, the reflections can be measured indirectly because the stray light could be calculated as the difference between the collimated beam and the non-collimated beam. A mathematical function for each case was fitted and it was found a functional relationship between them. It was found a greater amount of stray light measurements in certain positions of the intensity distribution matrix. Then a normalized matrix of stray light contributions was calculated. Finally, applying the results we made a diaphragm that reduces the value of the measurement uncertainty.