The industry standard for measuring brightness is ANSI lumens. When rated brightness is listed in anything but ANSI lumens, it is pretty much a meaningless number especially when trying to compare projectors from different manufacturers (see our article on Lux vs Lumens
Sometimes manufacturer may rate brightness in other ways like Lux, ISO Lumens, Peak Lumens etc. Since these are not a universal standard of measurement, these proprietary ratings can’t be used to compare brightness between projectors from different manufacturers. It might be helpful when comparing two “LUX” rated models in a manufacturer’s own lineup, but this spec can’t be used to compare brightness with another manufacturer’s projector.
For each projector we review, we measure brightest mode at full wide angle – this is with the iris wide open, so the most amount of light gets through. We take 3-4 readings at about 15-20% out from the center of the lens. That should give a pretty good approximation of ANSI lumens unless a projector’s brightness rolls off excessively at the edges, meaning the image is brighter in the center of the screen
For the rest of the modes, we measure them at mid-zoom, so the iris is closed halfway. This is because it is more common for a projector to be zoomed in a bit than installed at full wide angle.
For some interchangeable lens projectors, max brightness might vary depending on the lens utilized. Once a lens is detected, the projector may adjust its maximum brightness level. For example, below is a chart from Epson for their Pro L1755UNL projector.
Lenses compatible with Epson Pro L1755UNL
While brightness is important, it should never be the sole consideration when designing a projection system. There are other factors such as type of screen material, ambient light in the room, and several other factors that may affect the perceived brightness and clarity of the projection image.