It may be time to replace your projector lamp. Projector lamps dim as they age. Some projectors allow you to check the number of hours your lamp has been used through the built-in menu system. Check your user guide for information about this feature.
Just like any light bulb, projector bulbs have an expected operating time, called lamp life. This value is expressed in hours and represents the number of hours before the lamp is at half its original brightness.
The expected life of a lamp will vary based on the lamp technology and the projector; however, most projectors offer about 2000 hours. The lamp's success rate is based on a bell curve, so that a majority of (but not all) lamps will meet the lamp life hours specified. Some lamps will fail sooner and this is part of the acceptable operating range of the rating.
For projectors that are used under normal operating conditions (no more than three to five hours per day in a clean, relatively dust-free environment) the lamp will have the greatest likelihood of lasting through its entire rated lamp life.
There are several things you can do to increase your lamp life. Do not allow the projector to become overheated by ensuring that there is adequate clearance near the intake and exhaust vents.
Operate your projector in a clean, relatively dust-free environment.
Clean air filters every 3 months or more often if there is a lot of dust or contaminants in the room.
Striking the lamp ages the lamp as it causes slight changes to the shape of the electrodes that light the lamp, so light up your projector when you're ready to use it and avoid frequent on and offs.
Avoid shock to the lamp or projector.
If your projector has this feature, Use "Lamp Economy Mode" to lengthen the life of the lamp by reducing its brightness. In most cases you will get a 50% increase in lamp life with a 20% reduction in brightness and you will not likely notice the reduced lumen output.
Allow the projector fan to turn off after you power down and before you unplug the projector. The only exception to this is a projector that is designed to keep the fan turning for a brief period after removing power.