there are many led LCD now that have 4ms lag input >.>
as i already told
It seems that producers noticed the problem and begun to work in that way, so i think that we will see almost 0 lag input in future HDTV
And 4ms of lag input is almost not noticeable.
I also heard of a japanese brand of LCD monitor that could arrive at less than 2 msecs :O
So my question remains... WHERE are you getting this 4ms figure from? Are you getting it from the panel manufacturer? Or from people on forums who are actually testing it? How are they testing it? The only way to truly test for input lag is to use a distribution amp, line up two TVs, the TV you want to test, and a 0ms baseline (a TV you know for a fact has 0ms of lag)... then run a frame counter on it, and snap a photograph. Compare the numbers between the two displays on the photograph and you will have the actual lag.
Lots of people online do something called the "guitar hero / rock band test", where they hold up one of the guitars that are designed to compensate for lag, and it gives you a result. The problem is that these tests are highly inaccurate; on my own TV, (which I have calculated myself to 36ms of lag), I get a varied result every time. Doing something like 10 tests, I received results anywhere from 20ms to 80ms. Except for a truly scientific test like the one I posted above, you can't know the actual input lag.
Now if you got the 4ms figure from the panel manufacturer, then I can tell you they are not talking about input lag, but refresh rate; and once again, refresh rate is not the same as input lag. Most panel manufacturers claim to have anywhere between 2ms-8ms refresh rate... which in most cases, is a lie. If your TV had a 2ms refresh rate, that means that it should be able to display 500fps. There isn't a single TV on the consumer market that does more than 240fps, and that is an over 4ms refresh rate.
I see LCD monitors with a 2ms refresh rate "score"... that only does 60hz (fps)... That means in reality, it only has a refresh rate of 16.7ms, but it uses frame duplication and interpolation to mimic the remaining frames in order to prevent ghosting. You'll also notice that these refresh rates vary by technology. A 16ms IPS monitor will actually look better than a 4ms TN film monitor because the IP technology doesn't have the same worries about ghosting that a TN film monitor does, so they dont need to do the interpolation required to reduce ghosting, and the "score"