Front projector bulbs have a typical life expectancy of 2000 hours. I started calibrating my own displays a few years ago and as with any ‘hobby’, one learns things over time by speaking to others and learning things through practical experience. In my conversations with professional calibrators (who aren’t stingy with their advice), the 2000 hour rule is a pretty good one and universally accepted as “normal”. Projector bulb design is not hugely different between each manufacture. Most projectors have a low lamp and a high lamp mode (some call this different things, but it’s all the same). If you need to run the bulb in high lamp mode to get your preferred image luminance, life expectancy dips a bit, but not much. Some projectors are not affected by this at all, like the JVC projectors. Much of this is due to how well the projector bulb cooling system works. JVC’s have an excellent cooling system, which is why their life expectancy is not adversely affected by mode. But with this cooling, you have fan noise that is increased in high lamp mode, so pick your poison.
There is a common belief that just because the lamp still lights, the bulb does not need to be replaced. This is not entirely true. Even though the bulb lights and throws an image up on the screen, unless you have a light meter, it’s difficult to determine through casual viewing if the bulb needs to be replaced or not. As the bulb performance dips, you grow accustomed to this and do not notice it. I re-calibrate my projector every two hundred hours. Every time I do this, I have to make changes to keep grey scale and color gamut under a DE of 2. As the bulb ages, the light spectrum changes. Grey scale, gamma and gamut all start to drift. Lumens also changes, so white and black levels need to be adjusted to maintain my preferred luminance, which in turn affect grey scale, gamma and gamut.
Within the first 500 hours of use on a new bulb, lumens can be expected to decrease up to 50%. Lumens will remain relatively constant for the next 1000 hours or so, and then it does a nose dive.
But, if the image is still pleasing to you, all this really doesn’t matter and it’s not worth worrying about. Once you do, you will start down the rabbit hole and end up investing a lot of money and time to get back out the hole, but never really getting out.