Measurement model of circadian action factor of phosphor-converted white LEDs based on photometric, electrical, and thermal properties

Light stimulus is confirmed to have critical non-visual biological effects on human beings, and thus evaluation of lighting quality should not be limited to traditional visual performance. The circadian action factor (CAF) has been put forward to quantify such non-visual effects of light sources. This paper focuses on studying the photometric, electrical, and thermal properties of widely used phosphor-converted white LEDs (PC-WLEDs), and establishes an indirect measurement model of CAF regarding temperature, current and excitation wavelength. During modeling, the spectral power distribution of PC-WLEDs is described as an extended Gaussian function of the double-color (blue-yellow) spectrum. In verifications, the remarkable consistency is obtained between indirect measurements and direct calculations, while the maximum relative errors do not exceed 2.6% and the mean relative errors do not exceed 0.9%. The proposed measurement model involves a series of optical tests and calibrations, which are simple for LED system designers to comply with. It offers an effective tool to quantify the PC-WLEDs' non-visual biological effects on human beings, avoiding costly optical instruments and laborious calculations. Furthermore, it provides a potential theoretical foundation for realizing human-centric assessment, regulation and control of artificial lighting.