Short- and Long-Term Reliability Studies of Broadband Phosphor-Converted Red, Green, and White Light-Emitting Diodes

Phosphor-converted light-emitting diodes (LEDs) are now widely used in all kinds of illumination applications. Their structures are more involved compared with that of chip-only band-gap LEDs. We describe the extra manufacturing steps involved in phosphor-converted LED manufacturing and how these extra features impact the reliability of such devices. Our studies looked at both the short-term and long-term behavior of phosphor-based LEDs. Devices were tested for times ranging from a few hours to 40 000 hours. Some tests were performed at elevated temperatures of up to 70 °C. The light outputs of LEDs were studied as functions of time, temperature, and drive currents of up to 2.5 A. Shifts in chromaticity point of these LEDs were also investigated as functions of drive current and, thus, LED die temperature. These studies lead to several conclusions about the reliability and degradation behavior of phosphor-based LEDs that have been elaborated in this paper.