Conclusions
In this paper we obtained the highest test temperature to accelerate the life of the LED devices from the step
stress test, and the temperature could effectively shorten
the test time, without any new failure mode imported. The
higher test temperature could accelerate the degradation at
the early period of test, and with a consistent variation
between different levels at the later period of the
experiment. The high temperature test could fully explain
the degradation trend of life.
Making use of the data obtained through the reliability
test of LED products, we could determine the point
estimate and lower limiting value of the mean time to
failure with the specified confidence coefficient. The
formulas in 2.2 could also be used for the data gotten from
field use conditions, such as the actual ignition time and
the number of failure products, evaluated the mean time to
failure of LED products under the practical operating
conditions.