Hi,
I know the bulb has very long life but I'm also thinking of purchasing a reserve bulb (mine is USHIO S400DD) to keep, just in case the bulb went dark during the movie or so.

I wonder how long I can keep it? I meant, shelf life for the bulb? Since the operating life is rating 10k-20k hours, the shelf life should be longer...

Any idea?
tempoct

I seriously doubt there is any shelf life for one of these units. Indefinite. It'll last practically forever on the shelf so long as a cat doesn't knock it off onto the floor or something like that. No worries.