Ability to discriminate lightness values

Hi,

I read somewhere that due to visual interference the eye distinguishes
fewer luminance levels in dark areas than in light areas and that by
those means the number of luminance levels the eye can distinguish
decreases gradually from light to dark zones. Now does anybody know if
there is a certain proportion for that ability? If we´re able to
distinguish, say, ten times more values in areas of a given high
log/intensity than in those with a given low log/intensity?

Thanks for your input!
Johannes