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LCD – For the Novice and the Expert

 by Kristopher Kubicki on September 4, 2003 12:13 AM EST
63 Comments | Add A Comment
63 Comments

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.

Where do manufacturers get their specs? How to adjust your monitor correctly
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  • KristopherKubicki - Friday, September 5, 2003 - link

    #42 - this will be addressed in Part II =)

    Kristopher

  • Anonymous User - Friday, September 5, 2003 - link

    Very nice article. Easy to read, fun and very informative.

    However, as someone here stated earlier, the reference to how some companies manage to get more than the 262000 colours with the 16ms AUO substrate is missing. It seems that they do this by alternating two colours, which would in effect mean the actual total rise and fall time for that one colour is more than 16 ms. But perhaps this is to be discussed in the follow-up to the article? I'm really interested in reading about the grey-grey times for the panels, so I'll be looking forward to part II.

  • AbRASiON - Friday, September 5, 2003 - link

    Wouldn't touch one until it beats a CRT in every single way - period

    For work yes, sure right now, one res all day, no games, no worries.

    For home, multiple resolutions, more dos boxes - linux sessions (ok I don't have any but if I did) - games which I don't have a strong enough video card for native resolution etc etc.

    also the stupid ghosting / shading effect of the high refresh (16ms is too high)

    Until it beats a CRT in every single way - I'm not going over - EVEN IF CRT's end up costing more.
    Plus CRT's are getting better, my 22" Philips (100hz 1600x1200) is only like 45cm deep - quite short really considering.

  • virtualgames0 - Thursday, September 4, 2003 - link

    I think you missed a big issue with LCD image problems that I have commonly observed. Most LCDs are very dim, and almost all of them I've seen are nowhere close to comparable to a CRT, the only ones I've seen that were comparable was the NEC.
    Another problem I have commonly observed is that the majority of LCDs have very visable "gate lines(as you called it in the artlce), so then you can see that every pixel is seperated, and it makes everything look pixelated, and it feels like you're trying to look through that mesh...

  • spikemike - Thursday, September 4, 2003 - link

    I'm not 100% sure but i believe a 1280x1024 LCD monitor is actually built in a 5:4 ratio. So the pixels are still square.

  • n0d3 - Thursday, September 4, 2003 - link

    What I missed, and I'm sure it will be coverd in an update, was something more about resolutions. Here's why.

    Today, people seem to be using 'weird' or 'odd' resolutions a lot, basically because it seems better to have bigger numbers. For instance, 1280x960 is not acceptable (The drivers for my old Connect3d radeon 9000 did NOT support this resolution) however 1280x1024 is just fine. This strikes me as odd because monitors still use a 4:3 ratio. A lot of resolutions conform to this 'standard' 640x480 800x600 etc etc. But in the higher range they seem to 'cheat' a lot more. From what I can understand, this would cause a distorted display. This is very true for CRT's but LCD's seem to be heading that way asweel, wich is something I Don't get. I say this because it is always recommended to use an LCD at it's own resolution, wich is the amount of pixels on the substrate. I can hardly imagine that they would produce non 4:3 screens, allthough ofcourse it is possible.

    Some more info on this would be greatly appreciated since I could be wrong about this and tell people wrong things : )

    P.S. and yes, I know that if your monitor is capable of going up really high in resolution the distortion on lower resolutions should be minimal, nevertheless, it is deffinatly there.

  • Anonymous User - Thursday, September 4, 2003 - link

    Thanks for a very informative article.

    I have a Samsung 172T and I have to say the image quality is outstanding. I don't play a lot of FPS games, but for varied use including games and video,using DVI, there are no significant motion blur problems. This monitor is head and shoulders above comparable units I've seen, at least for general use. The price of this unit has dropped significantly since I bought mine almost a year ago. (It may be discontinued).

    Been an Anandtech reader since 1996. Keep up the great work!

  • spikemike - Thursday, September 4, 2003 - link

    I'm still not sure if you have it quite right, each subpixel can be independently controlled, you can get 16 shades of blue 16 shades of green and 16 shades of red, giving you 12bit color or 4096 total colors, the red blue and green do not depend on each other, red can be full on, blue can be "1/2" on and green can be off. The main problem was the lack of color, slow response times, and the fact that the information would "bleed" into the column, having one off pixel in a whole column of on pixels would decrease the over all brightness of that column

  • KristopherKubicki - Thursday, September 4, 2003 - link

    #33, I clarified the article a little to apply to both the EE folks and just the casual reader ;)

    Kristopher

  • spikemike - Thursday, September 4, 2003 - link

    oops i meant posts 29 and 30 were mine
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