Determination of stray light at the PTB goniophotometer facility |
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Authors: | G Bizjak M Lindemann A Sperling G Sauter |
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Affiliation: | 1.Laboratory of Lighting Engineering and Photometry,University of Ljubljana, Faculty of Electrical Engineering,Ljubljana,Slovenia;2.Department Photometry and Applied Radiometry,Physikalisch-Technische Bundesanstalt,Braunschweig,Germany |
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Abstract: | For improved luminous flux measurements, the Physikalisch-Technische Bundesanstalt (PTB) was equipped with a new robotic goniophotometer.
In order to characterize this instrument, to reduce the combined measurement uncertainty, and to determine the respective
uncertainty components, the influence of stray light on the measurement results was investigated. Considering the specific
structure of the robotic goniophotometer, stray light was measured on-line by means of a purpose-built “back-looking” photometer.
By this means, the influence of the luminous intensity distribution of each individual light source with regard to its stray
light could be considered. Before the first experimental application, the invented procedure was tested by means of calculations
using mathematical models. In this paper, the mathematical model for the calculation of stray light in the goniophotometer
room is presented together with the calculation results and the results of the first measurements. The achieved results indicate
that the recommended stray light measurements can decrease the total relative standard measurement uncertainty of luminous
flux measurements down to 2 × 10−3. |
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