The effects of current, temperature or their joint stress on the reliability of LED bulbs are studied and the failure mechanism of LED bulbs under each stress is investigated as well. It is found that the degradation of blue chips is the main failure mechanism of LED bulbs at room temperature when the current is as the accelerated stress. With the increase of current stress, the degeneration of phosphor gradually becomes the main failure mechanism, which resulted in the increases of both the correlated color temperature and the color rendering index of LED bulbs. Under the temperature stress or the joint current-temperature stress, the degeneration of phosphor is serious and the phenomenon of blackening appears. In addition, the yellowing and blackening occur in the lamps, driving power sources, LED brackets and aluminum substrates. It is indicated that the temperature stress accelerates the failure of LED bulbs more than the current stress. Finally, the lifetime of LED bulbs under the current stress is predicted by the extrapolation method.