[citation][nom]bildo123[/nom]Gosh darn it, and here I though my Samsung 24" LED monitor with its 12,000,000:1 CR was cool. Where do they get these numbers, throw a dart at the board and add six zeros to the end of it?[/citation]
They get these numbers by very simple mathematics. They're valid and mathematically meaningful (though not necessarily visually meaningful). They're the ratio of the minimum brightness of a pixel to the maximum brightness. If the minimum brightness is 0.1 nits and a maximum brightness of 2000 nits, the contrast ratio is 2000/0.1 = 20000.
LG is making a possiblly meaningful statement by taking the maximum brightness and dividing it by a minimum brightness which approaches 0 (as is the case with 'off' OLED pixels). As a divisor approaches 0, the result of any division approaches infinity, though, correctly, division by 0 is actually undefined.
If LG believes the minimum brightness is 0, they would be correct to state this TV has, 'undefined contrast ratio,' but that wouldn't look very good on a sign or brochure.