This study deals with the accelerated life test of high power phosphor converted white Light Emitting Diodes (High power LEDs). Samples were aged at $110^{circ}C$/85% RH and $130^{circ}C$/85% RH up to 900 hours under non-biased condition. The stress induced a luminous flux decay on LEDs in all the conditions. Aged devices exhibited modification of package silicon color from white to yellowish brown. The instability of the package contributes to the overall degradation of optical lens and structural degradations such as generating bubbles. The degradation mechanisms of lumen decay and reduction of spectrum intensity were ascribed to hygro-mechanical stress which results in package instabilities.