Design issue of novel type of an illuminance meter photometric head

Abstract

The aim of the study was to design a novel type of illuminance meter photometric head. The goal of this design was to get a head with high photometric efficiency and without spectral errors. The photometric head must be spectrally and cosine corrected. The most widely used cosine correction element is a diffusing plate. This type of illuminance meter head has a low photometric efficiency. For the low level signals, the low photometric efficiency can not be compensated by gain of an amplifier. Additionally the spectral characteristic of the diffusing cosine correction is partially spectrally selective. Also the spectral characteristic depends on the angle of incidence of the measured flux. The changes in the character of the spectral characteristic cause the spectral correction error of this type of illuminance meter photometric head. This error is the function of the angle of incidence of the measured light. Due to these facts a novel kind of cosine correction element was designed. This element is transparent and its spherical shape was determined from an analysis of the phenomena occurring in it. This kind of cosine correction element is much less spectrally selective than the diffusing plate and the illuminance meter photometric head equipped with it has a photometric efficiency 4.3 times higher than commercially available photometric heads.

Keywords:

• photometry
• illuminance meter
• light source
• luminous flux
• cosine correction element
• optical filters

Acknowledgements

This research was performed at Bialystok University of Technology, Faculty of Electrical Engineering under the S/WE/2/06 project.