In Projectors, What is the connection between increase in Lumens with decrease in Contrast Ratio?

Question

When the Lumens or the brightness increases, the Contrast Ratio decreases. What is the link between them.

Answer 1

For a properly calibrated projector it doesn't ... in fact under some conditions a higher rated lumen output projector with a lower contrast ratio can yield a higher perceived contrast ratio than a lower rated output projector with a higher contrast ratio.

As an aside, there are no mandatory standards for measuring contrast ratio, so published figures can be both very difficult to compare and very misleading.

Contrast ratio is determined by measuring the ratio of the output from white and black in an image. The exact way this is measured can lead to widely differing results. That said, for a properly calibrated projector lumens per se do not directly impact on contrast ratio.

It is however possible to get the effect you describe. Assuming no change in settings for a calibrated projector, switching to a brighter (higher lumen) lamp will, in essence, increase the white output (probably into a state described as "blooming") and will also make the black look more grey. Even though the white output is higher, the black output is increased more and the contrast ratio is therefore decreased.

Note that contrast as experienced in real life depends on the whole system which includes not only the projector, but the screen and the room itself. So contrast ratio taken in isolation can be misleading and must be considered in context.

For example, a poorly calibrated projector, an overdriven screen (due to too high light output and/or too high screen gain), reflective surfaces in the room or ambient light will all "destroy" contrast.

Quoting from the article at the link "contrast does not stand on its own! A higher image brightness level would yield a better perceived contrast ratio for a fixed level of ambient light. This means that a projector with a lower contrast ratio but with higher rated lumens output - may under certain light conditions - perform better than one with a higher contrast ratio but lower brightness level."

Hope this helps.