Setting your projector for its low power mode drops the brightness by about 20%. We concur, however in our reviews we find that the range can vary from as little as a 10% drop (barely detectable) to 30%, depending on the projector. Projector’s low power mode has two major benefits. First, the longer life. The typical projector claiming 2000 hours in full power claims 3000 hours in low power mode. That can differ, however. There are models out there that claim no increase of life in low power, and in some rare cases - a few Mitsubishi projectors, for example, claim 5000 hours in low power mode. The bulb may explode if they are used beyond there rated life.

Manufacturers design the mounts to limit damage, but you will need to get the projector serviced if your lamp does explode. Today’s projectors have two brightness modes, many now follow low and full power independently and adjust their warnings per your handling. Most warranties provided by manufacturers, are 90 days or 500 hours. In couple of years, however several companies that offer third party extended warranties on projectors have been offering lamp warranties as well.

source: http://www.projectorreviews.com/projectorlamps/ProjectorLampLife/index.php

Almost all home theaters and business organization depend on UHP lamp. These are lamps that use mercury. In projector you will see them called UPH (ultra high pressure), or any of a half dozen plus acronyms. Trying to tell them apart by the different names, is mostly a waste of time. UHP, UHM, NSH, UHE, etc, are the same thing, in almost all cases

Another type of lamp are very high end, and extremely bright projectors, and its totally different. They are Zenon lamps. Comparatively Zenon lamps have a better colour range that mercury lamp (UHP). They are expensive and have very a shorter life when compared to UHP lamps. They tend to start at over $1000, and typically have a lamp life of 500 to 1500 hours compared to UHP lamps good for 1500 to 5000 hours. They also are usually only found on projectors that sell for more than $10,000