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

Jan Audenaert,Peter Hanselaer,Paula C Acuña R,Frédéric B Leloup

doi:10.1364/oe.23.002240

Abstract

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.

Highlights

The far-field intensity distribution of a light source or luminaire, better known as the luminous intensity distribution (LID), is one of the key characteristics of a lighting device which is used to perform lighting calculations and simulations
While far-field goniophotometry (FFG) relies on illuminance data captured by a photometer, near-field goniophotometry (NFG) starts from the luminance distribution acquired by use of an imaging luminance measurement device (ILMD) [6, 7]
We introduce a new metric, which we call the discrepancy metric d, based on the fraction of the total luminous flux that is emitted in a different direction for the two LIDs I1,n and I2,n, obtained after normalization of I1 and I2 to the total luminous flux φt :

Summary

Introduction

The far-field intensity distribution of a light source or luminaire, better known as the luminous intensity distribution (LID), is one of the key characteristics of a lighting device which is used to perform lighting calculations and simulations. While far-field goniophotometry (FFG) relies on illuminance data captured by a photometer, NFG starts from the luminance distribution acquired by use of an imaging luminance measurement device (ILMD) [6, 7]. To this end, the ILMD revolves about the DUT, and captures luminance images for all directions in which light is emitted. NFG enables the simultaneous determination of both near-field related characteristics, such as the near-field illuminance [12] and the luminance distribution from the luminaire, as well as far-field related quantities, i.e., the LID and the total luminous flux. Some possible solutions to eliminate the dynamic range mismatch induced errors are proposed

Near-field goniophotometers

Devices under test

Comparison of measured LIDs

Findings

Discussion

Conclusion