Conclusion of the accelerated stress conditions affecting phosphor-converted LEDs using the fractional factorial design method

• We identified most influential stresses for phosphor converted LEDs’ degradation; temperature, humidity and operating state.
• Fractional factorial design was used to find out the most suitable combination of their levels for performing ALT.
• The combination of 70°C and 85%RH under operating was turned out to be the optimal.

A reliability test of phosphor-converted LEDs having the benefits of long life and high efficiency has been an important issue. The aim of this paper is to find out the most influential stress factors and their levels which have the biggest effects on the degradation of the light power of LEDs. The influential stress factors were determined through the preliminary tests, which included a high temperature accelerated test, a high temperature and a high humidity test under operating and non-operating conditions. By performing accelerated life testing under the stress conditions obtained by the fractional factorial design method, it was proven that the optimal set of stress conditions which affects the electrical and optical properties of LEDs the most is 70 °C at 85% humidity under operating.