An optimized model is established to improve the accuracy and efficiency of lifetime estimation for LED-based light bars. A Weibull function is used to fit test data of remaining luminance under two groups of accelerated stresses, and a method for determining the optimal test time is put forward. The results show that the optimized model for lifetime prediction best reflects the characteristic of luminance degradation. Furthermore, the error of the accelerated lifetime first decreases and then increases, finally decreasing again, which confirms that the method for determining the optimal test time is feasible given the level of accuracy required.