Thanks, but I found the answer on another site. (AVS)
Q16: Talk to me about the bulb. How much does it cost, how bright is it, how long does it last, do I want a bulb warranty?
A16: Mits is selling the bulbs for this set for $99 these days if you buy it from their website. Third party places are charging substantially more as of this writing (up to twice that price at some I've seen), so it probably is worthwhile to go directly to Mits for it. The part# is 915B403001. In theory, you can check how many hours of use your lamp has by entering <menu> 2 4 7 0. Unfortunately, this does not seem to work (reports impossibly low number) for 737 and C9 owners with the V41 011.00 firmware (as reported on that same screen as "DM Software").
^^ and that is exactly my case.
With a new bulb it's reporting 17 hours of use.. there is a problem with the firmware / version #.