Prediction of Lumen Depreciation and Color Shift for Phosphor-Converted White Light-Emitting Diodes Based on A Spectral Power Distribution Analysis Method

The spectral power distribution (SPD) is considered as the figureprint of a light emitting diode (LED). Based on the analysis on its SPD, a method to predict both lumen depreciation and color shift for the phosphor converted white LEDs (pc-LEDs) is proposed in this paper. First, the entire SPD of a pc-LED is predicted by superimposing two asymmetric double sigmoidal (Asym2sig) models, which represent the decomposed blue light and phosphor converted light peaks, respectively. For a better understanding of how the SPD model affects the photometric and colorimetric characteristics of a pc-LED, a sensitivity study of the SPD parameters is then performed on its luminous flux Φ, color coordinates CIE1976(u', v'). Second, the evolutionary process of the SPD is predicted for a pc-LED with the color temperature as 3000 K under degradation testing. And based on these predicted SPDs, the drift curves of Φ, u', v', and du'v' are further predicted. Finally, lifetimes of the pc-LED due to lumen depreciation and color shift are estimated simultaneously from the predicted Φ and du'v' drift curves.