Ageing characterization of colorimetric and photometric properties of commercial LED lamps

This paper analyzes the changes of spectral-derived characteristics of LED lamps during their operational life. The analysis is based upon a laboratory-controlled ageing experiment over 17 LED lamps samples. Each sample is put into its normal operating condition up to 20000 hours. As a comparison, lumen maintenance tests are also performed over another set of 9 lamps. In order to analyze the change in characteristics, the photometric and color quantities of the lamps are evaluated. The results show that the blue peak value and the re-emitted yellow component are decreasing independently over time. This implies that the ageing process induces a change of the color temperature and of the color rendering index of the output light. Four mathematical models are also proposed to investigate the relationship between color output and the operational time of the lamp. The selection of the best fitting is based upon the coefficients of determination from each model.