Both terms and their effects, need simultaneous review when discussing LED performance decline over time.

Depreciation commonly is used to refer to the decline in brightness over time as a light source is used, known as lamp lumen depreciation.

LEDs also degrade.

Degradation, many may think of chemical decomposition but there is also elegant degradation. One or both of these conditions seems commonly referred to, and one or both, may occur at the same time.

LED performance depreciates over time as less lumens are emitted. The more any light is used, the more a light source brightness dims over time.

LED lumen depreciation can be solely due to heat conditions. Research has verified this independent of LED operation.

Evidence of LED lamp lumen depreciation is useful, however we know in addition to lumen deprecation, LED Kelvin CCT (Correlated Color Temperature) changes over time.  If change in apparent colour appearance of an LED, and lumen depreciation are plotted at the same point, we can see how these changes may parallel each other in some LED sources, while for others, they may be independent.

Decline in LED lamp lumens and colour temperature change over time varies between manufacturers. It seems sensible to test LED Kelvin CCT measurements and plot them at the same time as Lumen measurements are taken when LED life performance testing is conducted.