Robot goniophotometry at PTB

Abstract

The total luminous flux of a light source is the complete integration of its spectral radiance distribution weighted with the photopic observer and taken over all parts of its surface and over the full solid angle of emittance. The spatial distributions are measured with various types of goniophotometers and the PTB robot goniophotometer is a new type with many unique features. It is built as an arrangement of three robots with arms of more than 6 m in length and with 7 degrees of freedom each. The extreme flexibility of the robots allows computer controlled tracks with variable radii and speeds up to 3 m and 1 m s−1, respectively. One robot aligns the light source and the two other robots move photometers and array spectrometers in their hemispheres simultaneously measuring planar illuminance and the related relative spectral distribution. The robot goniophotometer is optimized for the realisation of the luminous flux unit, the lumen and it is completely characterized in this report. The relevant properties and correction factors are explained, as well as the implementation of techniques for synchronisation and stabilisation of spatially resolved or integrated photometric and colorimetric quantities. Finally, all contributions are combined in the model of evaluation for the (total) luminous flux value and the measurement uncertainty associated with that value is evaluated in the presented uncertainty budget. The goniophotometric determination of the values for colorimetric quantities is explained for the total luminous flux and the spatially distributed radiant power.