Chromaticity stability of phosphor-converted white light-emitting diodes with an optical filter.

The thermal stability of blue LEDs and yellow YAG phosphor for blue-pumped white LEDs is critical to the performance of white LEDs, including the color properties and luminous efficacy. To investigate the thermal effect on the color properties of emitted white light, the junction temperature of the excitation blue LED was raised by increasing the supplied current. However, by choosing an optical filter with the appropriate transmittance spectrum for processing a portion of the blue light output and reexciting the secondary yellow emission, we observed a reduction in color instability and lower color temperature across the current range of 20–200 mA. Moreover, the color temperature distribution was improved.