I was reading a review comparing 2 LCDs by Samsung and the reviewer noted that LCDs that have a response time of 23 ms or less do not have ghosting. Is this true? I'm pretty sure that I've also read that there is still ghosting at 20-23 ms.
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Although there are some complexities, the basic equation is simple. You need a monitor that can respond as fast or faster than the refresh rate you're shoving at it. The complexities come when you consider that human eyes can't always see things at the fastest refresh rate so there's a limit to where this is applicable, but its a decent general rule. The bottom limit to refresh rates is usually 60Hz (which is loosely based on how fast the human eye can see, so its a good method to roughly consider the complexities I mentioned), which means 60 refreshes each second. If you divide a second by 60, you find that there is 16.67 ms between each refresh. Thus, at 60Hz, any panel that responds in 16ms or less should be able to display the picture with no ghosting. At 80Hz (a refresh rate that should be just better than anyone can detect), this comes down to 12.5ms.
Now, there have been some complaints of ghosting on 16ms monitors. The reason? they aren't really 16ms monitors all across the board, and the 16ms rating isn't necissarily measured correctly to start with. Whats being measured is the rise time of the pixel, or the time it takes to go from 5% of the total transition to 95% of the total transition. If it gets off to a slow start before 5% this can delay things (although that doesn't usually happen) and if it "rings" after it gets to the end point, that time isn't really considered. Also, the time it takes to transision depends a lot on how far its asked to go. Usually the listed responce time is measured from white-to-black or from black-to-white, but the response between shades of grey can be much higher. So, in a game thats switching between two grey shades, and if there is signifigant ringing or starting delay on the pixels, you can see ghosting on 16ms panels at 60Hz refresh rates.
Thats why there is a big hubub of people on this board waiting for 12ms panels. Not because they want to shove their refresh rates up to 80Hz and beyond (well, most of them don't want to), but so that the real delay that causes ghosting will hopefully be below the 16ms mark no matter what color its switching between and even including the delay and ring times. That way, a 60Hz refresh rate will actually refresh at 60Hz no matter what you throw at it.