so what would be an example of a 'good' contrast ratio and what would be an example of a 'bad' contrast ratio?
Actually there probably is neither good nor bad... just marketing hype.
"CR = "Ratio of light/dark on the same screen".
For most situations, the brightness needs to be turned down from the factory-set maximum. The comfortable amount of luminescence is approximately 120 nits. (1 nit = 1 candela/meter^2). The average "darkest black" most monitors can produce these days is approximately 0.6 nits. (On some models, it's .8 or .9) 120/.6 = 200 CR. Nothing impressive about THAT!
So, the makers try to be "creative" about these numbers [read LIE]. So what if the monitor has a brighness of 500? You won't normally use more than about 120 and you have to turn the brightness down to about 25%. (If the room is brightly lit or if viewed from a farther distance than normal, you can use a higher brigtness setting comfortably.)
Therefore, what we REALLY need for CR is (a) makers to engineer their LCDs so that their monitor's darkest black is actually darker than it is presently, and (b) to post in their specs the "actual luminescence of the darkest black when viewed with normal usable brightness"..... I haven't seen that one, have you?
Think about this... if the makers got their darkest black down to 0.1 nits, and we can "use" 120 nits of brightness, that's 120/.1 = 1200!
The place to find out the ACTUAL CR on a specific monitor is to check out x-bit labs or other reviewers who do things like measure colors with a colorimeter and measure luminescence electronically. When you do that, you often find the *maximum* CR is around 400-450 and the usuable CR is 200-250. (Another way, though subjective, is to read the Newegg reviewers' comments and notice which ones claim "really dark blacks"... that's the only important measure of CR.... and at least those models have a chance of having lower black luminescence.)
I happen to like Samsung. But their claim of "200:1 CR" is virtually meaningless... and this type of marketing is being used on most newer models. On an older model, a claimed CR of 700:1, is likely to be closer to the truth because when those models came to market the makers weren't making such exaggerated claims.
Just as claimed "response times" are mostly balloon juice, so are the claimed CRs.
(And BTW... the makers also screw with the specs on "viewing angles", too!!
😀 )