Start at a low setting at the light source

[DKL]

I'd say starting at a low setting will increase the lifetime expectancy a lot.
Mostly I see people starting at 70% or 80% just because they have a experience with bad guides.

[tester]

Starting at 30% or 40% depending on the diameter of the light guide does it for us.
This can save you serious money!

[Michel@SJD]

In our OR's the light power setting almost never exeeds 35% (300W systems) everything above is completely useless. The camera system wil regulate the extra lighting down. higher settings only result in more heat development and damage to the used materials.