The time required for a liquid crystal to change orientation.
Another way of saying it : The time required for a pixel to change from one luminance(light) level to another in a liquid crystal display.REFRESH RATE
The time alloted for each frame of video to be displayed on the screen divided into one second. Active matrix displays like LCD use the entire alloted time to display a frame.
(ie - each frame of video is displayed for 16.6666ms , 1/.016666sec = 60Hz)
(ie - each frame of video is displayed for 8.3333ms , 1/.0083333sec = 120 Hz)
Another way of saying it: DISPLAY FRAME RATE (note: does not have to equal the signal frame rate)
LCD blurring is a combination of long response-times and long hold-times. Reducing the response time with overdriving techniques does not help the hold-time. Reducing the hold time by increasing the refresh rate does not change the response time. You have to do both to really reduce blur.Big Note here:
You cannot just double the refresh rate of the display from 60 to 120Hz to reduce the hold-time and hence the blurring. This is because the display will just duplicate the incoming 60Hz signal frames resulting in no change in hold time. (ie 8.3333ms + 8.3333ms = 16.6666ms). You must either add a new frame (interpolation) or add a black frame (BFI) to get any improvement in motion. Both approaches result in 120Hz refresh rate with 8.3333ms hold time.
For a detailed description see the following link :why 120Hz?
from SID journals
"LCD Motion blur is a well known problem. Although many solutions have been proposed, some fundamental questions have not been answered yet. In this paper, we try to answer such questions. Specifically, we calculate the waveform and its blur width of a moving edge perceived on LCD screen for current LCD and the proposed four solutions of hold-type motion blur. We found that the slow response of current LCD is not a dominant factor of motion blur. The slow response of current LCD only contributes to 30% of the motion blur, while the hold-type rendering mode of LCD contributes to 70%. Therefore, fast LCD such as OCB itself does not significantly reduce motion blur. Fast LCD, on the other hand, is critical to the proposed three solutions of hold-type blur to avoid the ghosting artifact. With fast LCD, black data insertion and frame rate doubling can provide 50% reduction of motion blur. With both fast response LCD and fast backlight, backlight flashing can provide much higher reduction of motion blur. ©2005 Society for Information Display "see paper