Photodegradation of Epoxy LED Encapsulate and Its Repair for SDGs

The illumination of LED displays on highways has decreased throughout 25 years of use. The main cause is degradation of epoxy encapsulate due to long-term exposure to ultraviolet rays, and this is especially notable at the tip. Benzene rings in the epoxy resin photodissociate and weaken the encapsulate. This in turn leads to light scattering due to craze formation around the tip, where the degradation is most notable, ultimately leading to decreased luminance. In this study, the degraded epoxy encapsulate was repaired by applying clear acrylic coating with silicone on its surface. The acrylic paint completely filled the craze grooves, preventing diffused reflection and resulting in a complete recovery of luminance. Upon subjecting repaired LED to artificially accelerated degradation equivalent to approximately 30 years of outdoor exposure, the decline in luminance was held to 2％, and the post-repair durability was also sufficient. This repair method was applied to actual LED displays with notably poor visibility on highways and it was verified that the luminance could be sufficiently restored.