I replaced every light bulb in my apartment with LED's. It's now been over 5 years and I've seen zero instances of the bulbs getting dimmer. Zero. It has also made a great difference in my electric bill. The bill has gone down over 25%! Greg
I did the same as Greg. Big reduction in power consumption, which saved me money, which was great however they do not last long. I’ve probably replaced about a quarter of all my LEDs in any given year as they just start to randomly flicker. Maybe it’s a brand issue, but I think I bought almost all mine from Home Depot.
They do lose brightness over time, but it should be imperceptible. Loss of brightness is what the life expectancy rating on the packet is based on rather than the time to complete failure.
The life expectancy will be reduced somewhat when used in a confined fitting where the air can't circulate due to them running hotter.
I like the filament style led bulbs, which look alot like a tungsten bulb.