| Popis: |
The influence of phosphor and binder layer chemistries on the lumen maintenance and color stability of remote phosphor disks was examined using wet high-temperature operational lifetime testing (WHTOL). As part of the experimental matrix, two different correlated color temperature (CCT) values, 2,700 K and 5,000 K, were studied and each had a different binder chemistry. The 2,700 K samples used a urethane binder, whereas the 5,000 K samples used an acrylic binder. Experimental conditions were chosen to enable study of the binder and phosphor chemistries and to minimize photooxidation of the polycarbonate substrate. Under the more severe WHTOL conditions of 85 °C and 85% relative humidity (RH), absorption in the binder layer significantly reduced luminous flux and produced a blue color shift. The milder WHTOL conditions of 75 °C and 75% RH resulted in chemical changes in the binder layer that may alter its index of refraction. As a result, lumen maintenance remained high, but a slight yellow shift was found. The aging of remote phosphor products provides insights into the impact of materials on the performance of phosphors in an LED lighting system. |
