Accelerated life time testing and optical degradation of remote phosphor plates

In this investigation the thermal stability and life time of remote phosphor encapsulant plates, made from bisphenol-A polycarbonate (BPA-PC), are studied. Remote phosphor plates, combined with a blue-light LED source, could be used to produce white light with a correlated colour temperature (CCT) of 4000 K. Spectral power distribution (SPD) and photometric parameters of thermally-aged phosphor plates were measured by Integrated-Sphere. Results show that thermal ageing leads to a significant decrease in the luminous flux and chromatic properties of plates. The photometric properties of thermally-aged plates, monitored during the stress thermal ageing tests, showed a significant change both in the correlated colour temperature (CCT) and in the chromaticity coordinates (CIE x, y). It is also observed that there is a significant decay both in the phosphor yellow emission and in the blue peak intensity. The decrease in the luminous flux is strongly correlated to the deterioration of the chromatic properties of the phosphor plates. The results also show a significant decay of CCT, postulating that the degradation of the remote phosphor plates affects the efficiency of light and the colour of emitted light as well. The decrease of CCT takes place with almost the same kinetics as the lumen depreciation.