Originally Posted by GregLee
Important to what? Important to the numerical value of the quotient, yes, I suppose. But we're interested in human perception, here. Even though differences in very small denominators might be imperceptible to a human viewer, they make a large difference to the numerical value of contrast ratio. So for small values of the denominator, contrast ratio is not measuring anything we are interested in.
Small value denominator is the first thing you are interested in if contrast is important (assumes gaumat of both displays are equivalent). A black level difference between .0005 nits and .05 nits represents a 100:1 and is tremendously discernible in a darkened (or even moderately lit) room. Comparatively, going from 800 nits to 2000 nits won't yield a fraction of the perceived contrast improvement. Look at the slope of the lines for the attached luminescence vs visual perception charts, these clearly demonstrate my point. The human eye sensitivity to luminescence is logarithmic, with most of the perceived differences coming from lower levels (see how the line slope is nearly vertical at the low end).
There are two reasons why manufacturers tout high luminescence values:
1: It's somewhat easier to improve high luminances levels (relative to low) in a display. In a world driven by physical laws a 2x increase in overall light output is easier to achieve than a 10x,20x,100x, improvement in low luminescence capability.
2: This is a more more regrettable reason: most people will identify a unit change from 1000 to 2000 as a bigger difference than .005 to.05 (forget about the impact of a logarithmic scale). Display manufacturers can capitalize on this to market their product.
Again, if contrast is important to you then a display's black level performance (low luminescence capability) is paramount. The exception is if you watch a display in a very bright environment, that necessitates high output to compete with the ambient light. In that case you don't give a hoot about black level anyway as dark scenes won't be particularly visible.