Practical limitations of near-field goniophotometer measurements imposed by a dynamic range mismatch

Within near-field goniophotometry, measurement results of both an imaging luminance measurement device and a photometer detector are combined to generate the luminous intensity distribution of a light source. The simultaneous use of these two detectors may engender incorrect measurement results, due to their difference in dynamic range. In this paper, near-field and far-field based luminous intensity distribution measurements of two luminaires are presented, in order to exemplify the problem. Results demonstrate that the distributions obtained from near-field measurements may deviate from the correct intensity distribution, by an amount of up to 16% of the total luminous flux of the luminaire. A method to check for the correctness of the luminous intensity distribution from the near-field measurement, the so-called sanity check, is discussed. To conclude, some possible solutions to eliminate the dynamic range mismatch induced errors are treated.