All projector manufacturers work with a select group of lamp manufacturers (Philips, Osram, Ushio, Panasonic, Phoenix) who build the lamps installed in new projectors.
Each lamp comes from the manufacturer with a “rated lamp life”, usually between 1500 and 3000 hours. While far from the most important factor in selecting a projector, lamp life should at least be understood, because replacement lamp costs can add up.
While the most obvious definition of “lamp life” is it’s operating time, or, the length of time before the lamp goes dark (or begins to flicker). However, another factor in lamp life involves the slow decline in brightness. Reduced light output over time may degrade the usefulness of the lamp before it actually goes dark.
Lamp Operating Time
When a manufacturer states the rated lamp life, it does not mean that every lamp of that type they manufacture will keep operating to the end of the rated life. Rather it means at least 50% of the lamps will reach the rated lamp life. Because of manufacturing imperfections and projector owner disregard of protecting the lamp from overheating or rapid cooling, some lamps will fail early.
For example, according the Christie, a prominent projector manufacturer, given a typical lamp rated for 2000 hours of operation, approximately 5% of the total lamps produced will not reach 200 hours. Many manufacturers offer a pro-rated lamp warranty to compensate customers for this small percentage of very early lamp failure.
Lamp Brightness Decay
All projector lamps have a brightness decay curve that describes the decline in light output over time.
The figure above shows a typical projector lamp brightness decay curve. Note that after 500 hours the lamp will only be producing 65% of the original brightness, assuming the lamp is being operated in full output mode. If operated primarily in eco mode, the lamp will produce 75% of original brightness at 500 hours.
Projector lamp lumen depreciation of only 25% to 30% can alter the effectiveness of presentations made in rooms that are partially lit. While the original brightness of the lamp may have allowed bright projected images in only partially darkened rooms, after 500 hours or so, the brightness decay may require fully darkened rooms to achieve that same clarity of image.
The importance of brightness decay will vary depending on the projector application. However, it is important to understand that rated lamp life includes both the obvious condition of lamp failure as well as the more subtle, progressive process of lamp lumen depreciation.
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