An investigation of catastrophic failure in solid-state lamps exposed to harsh environment operational conditions

Abstract

Today’s lighting technology is steadily becoming more energy efficient and less toxic to the environment since the passing of the Energy Independence and Security Act of 2007 (EISA) [1]. EISA has mandated a higher energy efficiency standard for lighting products and the phase out of the common incandescent luminaire. This has led lighting manufacturers to pursue solid-state lighting (SSL) technologies for consumer lighting applications. However, two major roadblocks are hindering the transition process to SSL luminaires: cost and quality. In order to cut cost, manufactures are moving towards cheaper packaging materials and a variety of package architecture construction techniques which may potentially erode the quality of the luminaire and reduce its survivability in everyday applications. Typically, SSL luminaires are given product lifetimes of over twenty years based off of the IES TM-21-11 lighting standard which does not include moisture effects or large operational temperatures [2]. A group of recently released off-the-shelf luminaires have undergone a steady-state temperature humidity bias life test of 85°C/85%RH (85/85) to investigate the reliability in humid environment applications. The lack of accelerated test methods for luminaires to assess reliability prior to introduction into the marketplace does not exist in literature. There is a need for SSL physics based models for the assessment and prediction of a luminaire’s lifetime which is being spearheaded by the DOE. [3] In order to be fully accepted in the marketplace, SSL luminaires must be able to perform similarly to incandescent luminaires in these environments, as well as live up to the lifetime claims of manufacturers. A luminaire’s package architecture must be designed with performance factors in mind, as well as address some of the known and published package related failure mechanisms, such as carbonization of the encapsulant material, delamination, encapsulant yellowing, lens cracking, and phosphor thermal quenching [4]. Each failure mechanism produces the similar failure mode of lumen degradation predominately due to two contributing factors: high junction temperature and moisture ingress. The current state-of-the-art has focused on lumen degradation [5] - [19]. The investigation of catastrophic electrical driver failure of SSL replacement bulbs under harsh operating conditions has not been seen before in literature. This work followed the JEDEC standard JESD22-A101C of 85/85 with a one hour interval of applied voltage followed by a one hour interval of no applied voltage [20]. This test was performed continuously for each SSL luminaire until it became nonoperational, i.e. did not turn on. After the SSL luminaires were nonoperational, the failure modes and mechanisms were analyzed for each test vehicle. An important result from this work shows that harsh environmental conditions have a drastic effect on the survivability and reliability of the SSL bulbs when compared to the actual lifetime.