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Terry,

There could be a number of things happening that are causing a difference in measured light output. First of all, no two projectors will be exactly alike, and manufacturing tolerances can account for significant differences even in two units of the same projector model.

This projector has a 1.7:1 zoom, and while we always measure the projector at the widest angle lens setting, ProjectorReviews takes their readings at the lens's midpoint. Since the midpoint of the zoom isn't a set location (you have to eyeball it, more or less), it's possible that their numbers vary due to zoom changes between readings.

There are also differences in light meters, and sometimes these differences are exaggerated by where the user holds the meter while taking the readings. There could also be an error in someone's readings, but without re-testing both projectors there's no way to tell who, if anyone, is wrong.

Then there are differences in settings. Since the PE401H is a DLP projector, it is possible to change white light output significantly by using BrilliantColor. If one projector had BC enabled and the other did not, that would easily account for a 1,000 lumen difference.

Long story short: there are a lot of factors that can cause differences between two projectors, and without seeing both projectors, there's no way to tell which readings are correct. They may both be correct. They may both be wrong.

Also, as a minor correction: Projector Reviews actually measured 4685 lumens in Bright mode at full wide zoom, compared to our reading of 3975. So the two differences you pointed out are far from the only ones. If you corrected all of their numbers for zoom lens light reduction, none of the image modes match up correctly. Because of the difference in testing methods, it's not a straight-up comparison.