## 1 Introduction  
With the advancement of LED lighting and display technology, LED products that ensure high efficiency and cost-effectiveness are gradually replacing traditional lamp beads in various application fields. However, as the reliability of LED chips continues to improve, the failure data generated by rated stress tests are becoming fewer and fewer, or even fault-free. It is necessary to adopt accelerated test methods to accelerate the product failure process while keeping the failure mechanism unchanged, reduce test time, and shorten the development progress. The failure mechanisms of LEDs are divided into three categories: the semiconductors, interconnects, and the package [1]. Failure mechanisms related to semiconductors include the generation and movement of defects and dislocations, et al. Interconnection-related failure mechanisms include wire breakage and wire ball bond fatigue induced by electrical overstress, et al. Encapsulation-related failure mechanisms include encapsulant, delamination, encapsulant yellowing, and lens cracking, et al. High current, poor assembly, and moisture intrusion can be classified as external causes of LED failure [2; 3; 4]. As reviewed in paper [1], light output degradation is the main failure mode of LEDs, which is caused by hydromechanical stress and electrical stress in addition to thermal stress. The reliability of LED chips heavily depends on the conditions under which the system runs, in particular, the temperature and the humidity [5]; as a result, the traditional simple stress test cannot truly reproduce the actual working environment. Therefore, it is necessary to study the multi-stress accelerated life assessment method to accurately obtain the life data of LED chips in the actual use environment. Currently, many scientists have conducted research on multi-stress acceleration models. [PERSON] deducted that temperature is the most significant factor affecting the life of LEDs, followed by humidity, but did not take into account its coupling effect [6]. [PERSON] combined the traditional acceleration model and proposed a dual-stress and triple-stress accelerated life model suitable for custom-circuit samples, electronic fuze, and smart electricity meters to predict reliability indicators [7]. [PERSON] et al. proposed some reliability tests and evaluation methods for accelerated life tests and accelerated degradation test models [8; 9; 10]. [PERSON] et al. studied the prediction of UV LED life, but they only considered the UV LED life test at room temperature, which lasted more than 8000 h. They did not consider the impact of the actual environment on the UV LED, and the error between the life and the actual value was quite large [11]. [PERSON] designed a step-stress accelerated degradation test in the UV LED life test, with temperature and drive current as gradually increasing loads, and different failure mechanisms occurred in the test. The author did not consider the coupling of temperature and current in the test [12]. [PERSON] proposed a Bayesian approach to estimate the remaining useful life of high-power white light LED packages and lamps without considering the stress coupling relationship in the accelerated degradation test [13]. However, the use of multi-stress acceleration models ignores the mutual influence between stresses and does not consider the true correlation between stresses, resulting in a large deviation in the estimated life of the test. [PERSON] proposed a general multi-stress acceleration model considering generalized coupling, but only simulation data are available [14]. Although [PERSON] considered stress coupling, he directly concluded that humidity and current stress were not coupled based on expert experience [15]. In addition, there were fewer samples for different stress experiments, a smaller current stress interval, and a shorter test time, which resulted in the coupling of temperature, humidity, and current being ignored.