That's actually no good for flashlight bulbs as it won't allow the gas fill to return tungsten back to the filament.
This is referring to the
halogen cycle which only applies to... halogen bulbs. So yes in that case it's best to run them at rated voltage or perhaps slightly below. But for regular incandescent bulbs (as in: no halogen gasses inside the bulb), it's different: lower working voltage = exponentially longer life. To find out more, search the intertubes for "lamp rerating".
Myself I own only a few incandescent flashlights. And I wouldn't consider stocking more than say, 3..5 spare bulbs for each. Unless they get thrown in my lap for free (which happens occasionally
).
Why? I rarely use these lights anyway. And each bulb represent a # of hours runtime. Say each bulb is designed to last ~1000h
at rated voltage (do note that especially small bulbs are often overvolted in their normal applications). A stock of eg. 5 spare bulbs then represents 5000hrs of runtime, which is ~30 weeks or more than 1/2
year of continuous operation. No way I hit anywhere close to that with occasionally-for-fun use.
Yes there's drops etc, but I'm careful with my gear. So given the above it just doesn't make sense to keep money tied up in a lifetime stock of spare bulbs. Never mind that it's only a matter of time before popular bulb types are produced new again (if not already happening). Same as happened with old media like cassette tapes, vinyl records etc, or even some types of electronics tubes :huh: (no I kid you not!).