What is response time? Why do I need to care? How low is quick enough? How is it measured? What response time should my LCD have? Will my games play ok if my response time is x ms?
One of the major measurements of an LCD is its response time. Many people choose an LCD based on this measurement without really knowing what it measures and how it is measured. In a nut shell response time is the time it takes a pixel to go from one color to another and back again. The response time of an LCD is actually the total response time - the time it takes a pixel to rise to a color plus the time it takes that same pixel to fall again back to the original color. The lower the response times the quicker and smoother a moving image will appear on an LCD.
Enough stalling! I want to do games, movies, etc. What should the response time of my next LCD be?
- It is generally accepted that 16ms and below is good enough for fast gamming. (Unreal 2k4, Quake III, etc.)
At 16ms and lower response times in LCDs can support refresh rates of 62.5Hz or higher. This will lead to a max frame rate of FPS games at 62.5fps for 16ms or higher for lower response times. - Most post I read agree that 30ms and below is acceptable for most movie viewing. (30ms = 33.3 refresh rate which is still higher than 29.97fps TV or 24fps Movie) To get technical interlaced video effectively runs at 59.94fps since it paints 2 interlaced fields per frame. (29.97 frames per second * 2 fields per frame = 59.94) However, for most viewers 30ms is enough to produce a smooth image for a typical movie, but some people prefer 25ms or better for movies.
What will effect the LCD's response time?
- As a general rule the LCD will have higher response time as you reduce the contrast setting. So depending on what your contrast is set to will affect your response times.
- There is no standardization on how a manufacturer measures its response time on an LCD. This leads to interpretation by the manufacturer. Based on how and when a manufacturer chooses to measure its response times can make a direct comparison between two different LCDs inaccurate or misleading.
- Response times vary based on the color the pixel is coming from and going to. For example if on a certain LCD the pixel is coming from black and going to grey-50 the response time could be 20ms. If on that same LCD the pixel was coming from black and going to grey-175 the response time would be 30ms.
Many FPS games are dark and use lots of darker shades of grey. The response time from black to grey-175 could be higher than the manufacturers stated response time. Therefore, a better representative measurement would be to take an average of all colors turn times since all applications don't operate solely in pure white and pure black but in grey values. Some manufacturers provide a matrix response time data sheet on their LCD panels for the varying shades of grey.
Are all LCD panels created equal?
- There are four basic types of LCD panels. Each type has a different matrix on its individual rise and fall times of a pixel. On one type the pixel may fall faster than it rises and vice versa. For example a typical TN matrix might have a 25ms rise time and a 5ms fall time for a total time of 30ms. A typical MVA or PVA matrix might have a 15ms rise time and a 15ms fall time. Each type in this example has a total response time of 30ms. However, the MVA and PVA would appear faster on scrolling text than the TN type even though their total response times are equal.
So what does all this mean to me?
- Basically, if you skipped the whole thing know this: The response time on the box of an LCD is important, but it should not be considered an absolute value. You want the lowest response time that you can afford, but in some cases a particular LCD may have a higher response time listed on the box yet still meet your needs.
- All LCD panels are not created nor measured equally. This explains why for one person a given response time rating may by sufficient, yet for another person that same response time may be too slow. It depends on what you plan on viewing on the LCD, how honest and clear the manufacturer stated their response time, and other variables like the contrast setting.
What is the best way to evaluate an LCD's response time/determine if it will meet my needs?
- The simple answer is just watch something on it and make up your own mind. Depending on how much grey is in the viewing content, how fast that content is, the response times of that LCD, and user preference can all determine if a particular LCD is right for you.
For excellent technical reading and where I obtained some of my facts surf over to the following:
X-bit’s Guide: Contemporary LCD Monitor Parameters and Characteristics