What is a contrast ratio?

Question

How much difference is between 30,000 and 50,000 contrast ratio?

Answer 1

In principle, contrast ratio is the ratio of white over black.

For the same white level, higher contrast means you get better blacks.

For LCDs, such high numbers usually define dynamic  contrast, which is pretty much meaningless.  There is more to picture than contrast, so make sure you have a chance to watch real-video on both sets before you decide what to buy.

Answer 2

Contrast ratio is basically how black the black colors are compared to the whites.

Contrast ratio measurements in the tv industry are arbitrary as there is no industry standard to measure contrast.  

Instead of focusing on that number look at the response time, whether the set is 60hz or 120, and that the set will be name brand (preferably Sony, Samsung or Sharp).