Well in the case of my 25% drop after 400 hours, I have very few bulb strikes as I use my projector for many hours at a time. Never less than 3 hours at once I would say and usually longer per use.
Does your room have A/C? I've noticed a while ago (before getting my rs2000) that in a non A/C room, during long sessions, the ambiant temp can go up and that can have a negative impact on brightness.
That's one of the reasons why I invested in A/C for the cinema room.
In small room, the PJ can contribute to a significant raise of temp that not only impacts on the calibration (especially greyscale) but also on brightness/lamp life, as least as far as I could observe.
Since I make sure that A/C is on especially during long sessions (calibration or watching), I don't notice such big drops in brightness.
One other possible reason is that when you measure brightness in respect to lamp life or to check the lamp spec, the only mode to use is high bright (profile off, uncalibrated, no color temp correction).
Every other mode can be impacted by an Autocal for example, especially if you use a poor Spyder for color, as it will overcorrect. A drop in brightness caused by a poor Spyder can be up to 15% and more if it's really off and nevertheless used for color. Using a proper meter (say an i1pro) for color can claim back that much wasted brightness.
So I only use high bright / profile off to monitor bulb life, as that's the only "factory" mode that remains "factory" even if you use Autocal. Unless you restore the INIT file before each brightness measurement, which is unlikely.
It is, by the way, the mode that JVC uses to define the specs (at shortest throw).
It is also the mode used to calculate native on/off contrast, but at longest throw this time.
When I stopped using Autocal and started using the native color gamut with a large 3D LUT (profile off with the filter), I gained another 5-10% in brightness compared to an Autocal with the i1pro2.
So the calibration isn't only more accurate, it's also brighter.
Please note: I am not saying that a Spyder always wastes brightness when used for color, or that anyone will gain brightness if they stop using Autocal. Autocal is great, it's just not my preferred way to calibrate anymore now that better options are available in my situation (external 3D LUT available for all my sources and not just for my HTPC). The need to calibrate non-HTPC sources was the main reason why I was using Autocal previously. I would still be using it today if I didn't have the ability to use a 3D LUT for all my sources.
