Choosing An LCD Monitor (Part 2): Response Time

Posted on Thursday, September 28 2006 @ 14:05 CEST by Thomas De Maesschalck
This is the second part of the LCD display buying guide, here's the first part.

If Contrast Ratios and Nit levels haven't confused you enough, then let's bring more terms into the discussion! In this 2nd part of "Choosing An LCD Monitor", we're going to take a look at response times, and how there are two very important and yet different response time specifications.

Black-To-White-To-Black Response Time

When LCDs began surfacing in the consumer market more noticeably a few years ago due to lower price costs, a measurement of how well the monitor responded to changes to input data on the screen was usually observed in the specifications of the product. This became known as Response Time.

The response times of various monitors were expressed in terms of milliseconds and gave the consumer an idea of how fast the LCD monitor could display images. At the time, playing movie content on the computer was just catching on and becoming rather popular and convenient.

The response time of the LCD monitor was not only expressed in milliseconds, but additionally meant how long it took for a pixel of the monitor (which is the smallest unit of an image on an LCD monitor) to change from "off" to "on" and back to "off" again. This also meant how quickly a monitor could change from black to white to back once again.

Initially, lower millisecond ratings meant the higher quality of the monitor and the quicker it could draw images as they were being fed to the monitor's input panel. If the response time was slower than another monitor, this meant the slower monitor could not interpret the transition of one image to another, and created "afterimages" or a blurring effect. Many users also refer to this effect as ghosting.

Gray-To-Gray Response Time

While response time was a good indicator of a monitor's performance, it did not demonstrate another important specification which was transitions between gray levels (i.e., Gray-To-Gray response time). Images include gray levels of color and not just black and white colors, so recently, LCD monitor specifications have included Gray-To-Gray response times.

Gray-To-Gray response times are a little more telling of a monitor because an LCD's crystal molecules respond faster to the high voltage needed for black-to-white transitions versus the lower voltage requirement for gray-to-gray transitions. What this means is that it can actually take longer for gray level transitions to finish, which will result in lower response times, regardless of the black-to-white response time.

Potential LCD users might wonder why the gray transitions would be more difficult for a monitor to produce than black-to-white transitions. A higher voltage excites the LCD crystal molecules much more easily than at a lower voltage.

A Tale Of Two Monitors

When purchasing an LCD monitor, you may come across two of them (or more) which have the same black-to-white response times. It is recommended you also look at the gray-to-gray response times. Most LCD manufacturers are now listing gray-to-gray response times, so this certainly helps you make the right choice.

For example, Monitor A could have a black-to-white response time of 16ms, while Monitor B has 20ms. You would normally think the one with the faster response time is better, but if the gray-to-gray response time of Monitor A is higher than Monitor B, ghosting and afterimage effects will be more prevalent for Monitor A. Today, LCD manufacturers are still playing around with both of these response times. Many response times are not quantified so you do not know which response time the numbers are supposed to be referenced from.

Investigate And Ask

The best investment, is a wise investment. Accordingly, if you're going to spend a significant amount, you really should contact the manufacturer if the response time of the LCD monitor are unclear. Demand an answer. A few emails and even a few calls to your prospective LCD purchase could save you a lot of trouble.

©2006 by Jason Busch

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Re: Choosing An LCD Monitor (Part 2): Response Time
by Anonymous on Thursday, September 28 2006 @ 16:23 CEST
I didn't know about the voltage differences, it makes sense. To the point and informative read.