Packaging-related
- Epoxy degradation Some materials of the plastic package tend to yellow when subjected to heat, causing partial absorption (and therefore loss of efficiency) of the affected wavelengths.
- Thermal stress Sudden failures are most often caused by thermal stresses. When the epoxy resin package reaches its glass transition temperature, it starts rapidly expanding, causing mechanical stresses on the semiconductor and the bonded contact, weakening it or even tearing it off. Conversely, very low temperatures can cause cracking of the packaging.
- Differentiated phosphor degeneration. The different phosphors used in white LEDs tend to degrade with heat and age, but at different rates causing changes in the produced light color, for example, purple and pink LEDs often use an organic phosphor formulation which may degrade after just a few hours of operation causing a major shift in output color.
Read more about this topic: List Of LED Failure Modes