Characterization of photometers for high illuminance levels

Photometers measuring high illuminance levels, ranging up to 200,000 lux, often undergo significant heating during operation. This temperature rise affects critical components - the spectral matching filter, diffuser, and silicon photodiode - thereby impacting the accuracy of illuminance measurements and contributing to measurement uncertainties. The study investigates the temperature dependence of the luminous responsivity, showing that as temperature increases, the photodiode's sensitivity rises, and the transmission characteristics of filters may change, especially in narrowband spectra such as coloured light sources. The degree of this effect varies based on photometer design and materials. Thermostatic stabilization, commonly integrated into laboratory-grade photometers, regulates the internal temperature, minimizing deviations caused by ambient conditions and stabilizing measurements across high illuminance levels. Nevertheless, temperature effects cannot be fully neglected even with thermostabilisation. The findings highlight the necessity of understanding temperature effects to enhance accuracy and reliability in photometric calibration processes.