LCD – For the Novice and the Expert
by Kristopher Kubicki on September 4, 2003 12:13 AM EST- Posted in
- Displays
Testing procedures
Manufacturers often post specifications that bring them the largest advantage. Below is a small cross-section of how some of those specifications are obtained in the lab (and what they mean).Luminescence [cd/m2]: This measurement is the basis for most other measurements concerning displays. Candela per meter squared basically just lets us know how bright the image is.
Contrast Ratio [N/A]: This is a unique measurement in the respect that it has no units. Purists argue that this is one of the most confusing and misleading specifications on an LCD. In any case, the Full Screen Contrast Ratio is obtained by placing the display in a dark room. The screen is turned to black and the luminescence obtained (Lb). The screen is then turned to white and the luminescence obtained (Lw). The ratio is then a measurement of the Lw versus Lb. Manufacturers sometimes skew this number by not taking the luminescence values on center.
Response Time [milliseconds]: This is a very important figure for gamers. LCDs do not rely on refresh rates for screen redraws. Instead, they rely on the time it takes a single pixel to power on and off. This measurement is done by placing the screen in a dark room and turning the screen to black. The time it takes the screen to go from black to white is the “Rising” response time, and the time it takes to go from white back to black is the “Falling” response time. Adding both of these together gives the average/typical response time. The important fact to remember is that even though it takes 16ms for the pixel to completely untwist and then twist, most media do not solely consist of extreme shades of color.
For example, a pixel may be illuminated in a grey fashion (i.e. all sub-pixels are half untwisted). According to a lot of our substrate insiders, the Gray-to-Gray response time is much more important. Due to electrical modulation, the response time from one gray half tone to another gray half tone can be as high as 100ms on a typical VA monitor!
Viewing Angle [degrees]: Viewing angle is a very straightforward measurement that can be done very easily with very little equipment. Because the LCD twists and untwists, the human eye has trouble seeing the crystal at different angles. At extreme angles, usually around 80 degrees from center, the human eye cannot determine if the crystal is twisted or untwisted and thus, the image doesn’t really look like anything. Using a protractor, you can determine the viewing angle of your monitor by rotating it until you cannot see the image anymore – then measuring the angle.
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KristopherKubicki - Thursday, September 4, 2003 - link
#16 - very interesting. Thank you for this information as I will pass it on to others.#19 - Sorry James (whips himself with a wet noddle.) Next time I do something like this I will spend a little more time talking about the BL.
#20 - Im a big Local H fan, but the subtitle actually is derived from an old excellent Stanely Kubrick movie. http://www.imdb.com/title/tt0057012/
#21 - We have had some troubles obtaining Hyundai and LG.Philips based monitors. Fujitsu and Samsung (and AUO I guess) kind of dominate the Us market. I will see if I cant get some more for our internation readers.
#22 - That would be the contrast ratio. However, as we have mentioned before, this measurement seems to vary so much from manufacturer to manufacturer, that it becomes almost useless.
Thanks for all the positive feedback!
Cheers,
Kristopher
Anonymous User - Thursday, September 4, 2003 - link
A point that usually isn't addressed when talking about LCD displays (perhaps it's just me) is the intensity of the colors. I don't care how many variations of pastel an LCD is capable of, the colors just look washed out to me. Is there a measurement that quantifies this?Anonymous User - Thursday, September 4, 2003 - link
Yeah, I was reading the article and immediately wondered why Hyundai is not cited as panel manufacturer.I am the VERY HAPPY owner of an Hercules Prophetview 920DVI Black Edition, second generation (same panel as the Hyundai Q17, 20ms response time). I bought it because of an excellent THG review, based on other input as well, based on its great look, based on its price at that time and based on the panel replacement policy by Hercules that seems (not a single dead pixel, yet...) better than others.
Also, as can be seen in several reviews online and as I personally experienced at a LAN where a buddy brought his Hitachi CML174, the response time in games feels a little better on my 20ms than on his 16ms...
Just a single annoyance, maybe due to my R8500LE DVI output, is that, in Quake3, when there is a lot of 'shiny' light/reflection (as in the second solo level, the fire wall/column when getting inside, and having to choose left or right), there is a lot of tearing/banding, especially visible on these shiny/reflective surfaces...
Does not appear on the theoretically slower 172T on a R9700Pro.....
Anonymous User - Thursday, September 4, 2003 - link
This has nothing to do with actual LCD's but I loved the Local H reference in the article subtitle.Matt
Anonymous User - Thursday, September 4, 2003 - link
Glad to see the article Kristopher, but how could you have a whole article about LCD's without discussing the all important BACKLIGHT.When you look at a modern active matrix LCD you're basically staring straight into a fluorescent bulb--the backlight. The appearance of the substrate can be significantly affected by the quality of the backlight, and when you're using the LCD to perform everyday work like word processing or working in a spreadsheet then 90 percent of the screen is pure white and all you're really seeing IS the backlight.
In that situation the experience using the LCD is highly dependent on characteristics of the backlight--such as the flicker rate of the fluorescent backlight or any anomalies in the backlight's spectrum of colors.
It's true that these factors are usually glossed over by mainstream PC magazines I was expecting Anandtech to cover these issues.
James
Anonymous User - Thursday, September 4, 2003 - link
When I got my monitor. I though it had few dead pixels but in reality it was a little specks of something on the screen, In which case whipping it fixed the "dead pixels".Anonymous User - Thursday, September 4, 2003 - link
I have been looking at getting an LCD for a little while now and found this artical to be very interesting. One thing I would like to comment on is you talk about large screen LCD monitors and how there is a lack of a choice. This is true but one thing I have been looking at is getting a Samsung LCD HDTV Monitor. These have a 16ms response time and reach the larger sizes and have PC hook ups in DVI and a regular 15 pin connector. Of course all of this is assuming that price is no option, as these screens are expensive. Samsung already has a 32inch screen that looks great, model LTN325W, and is gonna be putting out a 26 inch mondel, LTN265W in near future. I wonder how these screens would stack against the LCD monitors you discussed.rapsac - Thursday, September 4, 2003 - link
One important conclusion is missing in the article:On page 10 in the list of brands with the same panel you can see that the # of colors change from manufacturer to manufacturer. Fact is that this specific panel only uses 18bit color info, resulting in 262200 colors. All companies that state more colors LIE.
The controllers they use for these panels use some form of interpolation to fake more colors, but this will never result in as good a picture as with 24 bit panels.
Also, the interpolation is based on FRC (frame rate control); hereby the pixels get different color info each refresh. This results in visible noise (look at any Acer/BenQ from closeby, chances are you'll see it straight away) and it will also completly ruin the response times as more than 1 refresh is neccesary to give the pixel its color.
I have had a lengthy discussion with BenQ about this. The only result is that they promised to state the #colors of models with interpolation to 16M instead of 16.7M, at least this gives the end user a means to detect a 262k panel with interpolation.
Anyway, I've been screwed by BenQ with a 15" FP567 and whenever I see a LCD review I try to warn ppl. Acer and Benq (and lots of other brands) use these 262k panels in almost all their cheap models, so watch out and demand that you can return it if the specs are completly false.
Anonymous User - Thursday, September 4, 2003 - link
Its a shame that this article did not point out the Hyundai panels. I have an L70S with a 16ms response time, and the picture quality is very good, and I can't perceive any "ghosting." The big downside to this monitor is the lack of DVI. Has anyone else had good experiences with the Hyundai panels?PrinceGaz - Thursday, September 4, 2003 - link
Excellent article.@#13: "A good article.I my self use CML174.
Made a lot of difference to my eyes compared to CRT."
Were you by any chance running your CRT at the default refresh-rate of 60hz? Thats the usual reason people claim they cause eye-strain (often because they don't know how to change it). For the price of a new LCD display, you could get a larger high-quality CRT monitor capable of running at 85hz or higher (ideally 100hz) and you'd be amazed how much better it is than any LCD. On the other hand you could just increase the refresh-rate on the old one and save some cash.
Myself I use the 22" CRT Mitsubishi DiamondPro 2070SB with a 20" visible display at 1600x1200 @ 100hz and the picture is fantastic. Theres no LCD available which could come close to it especially for gaming. Unless you need to take it to a LAN party :)