[HPsquared]

Light bulbs (including LEDs) are similar. If you use them at slightly lower then their maximum rating, things tend to last a LOT longer. The "Dubai lamp" uses this concept - oversized LEDs that are derated, and last a very long time (100k hours). You can do the same by buying oversized dimmable LEDs and simply turning down the brightness.

[butvacuum]

That doesn't help nearly as much as reducing the current through them. And, PWM doesn't change the lumens per watt at all.