Lumens is a unit of measurement for light, so why is it called ANSI Lumens on projectors?
The light output from a projector is not even. The image tends to be brighter in the centre and gets dimmer towards the edges. Projector manufacturers in the past used to quote Lumens as the light output specification for their projectors. This, however, was misleading as the figure quoted often related to the brightest part of the image, usually the centre of the screen. The American National Standards Institute (hence ANSI) in 1992 introduced a measurement system whereby the Lumen light output is measured at 9 specific points on the projected white image and the readings are then added together and divided by 9. This provides an average light level in ANSI Lumens and this is what we use to measure the light level of projectors.
