Abstract: Based on the lognormal distribution, the efficiencies for the type-I censored step-up-stress and step-down-stress accelerated life tests are compared and analyzed according to the first criterion by comparing the total numbers of failure products and based on the second criterion by comparing the conditional expectations of life. Also for the type-II censored step-up-stress and step-down-stress accelerated life tests, the efficiencies for these two tests are compared and analyzed according to the third criterion by comparing the total test time and based on the fourth criterion by comparing the sample means. Afterwards the efficiencies for the two kinds of tests under these four different criterions are compared by using a large amount of Monte-Carlo simulations in one example of simple step-up-stress and step-down-stress accelerated life tests. As a result of this example, we see that the step-down-stress accelerated life test is available to improve the test efficiency and it is superior to the step-up-stress accelerated life test. Therefore, it is worthwhile to popularize the step-down-stress accelerated life test.

Key words: Efficiency, Lognormal distribution, Step-down-stress accelerated life test, Step-up-stress accelerated life test, Type-I censored life test