Visible Lumen Depreciation of a White LED based Indicator

I noticed yesterday that after nine years the LED in the num lock indicator on my laptop has faded really noticeably compared to the caps lock and hard disc activity indicators next to it.

While they look blue in the photo the LEDs are actually white, they just shine directly through the case of the laptop which is transparent blue.

Just thought it was quite interesting to be actually able to see the effect so obviously in person on such an everyday item. These three LEDs looked identical in brightness when the machine was new.