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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Anonymous User - Friday, October 17, 2003 - link
I'd just like to bump #60. He asks some great questions - anyone have any answers?The 15" laptop 1600x1200 vs 19" desktop version has always bothered me. I wish I could buy my ThinkPad's display as a standalone device!
Anonymous User - Monday, September 15, 2003 - link
Thank you Kristopher for your informative article.I have been staring at a computer or TV monitor for over 25 years and between the CRT and aging, my eyes have been getting worst every year. I am interested in getting the best video quality monitor for under $1000 per monitor. After reading your article, I would assume that a CRT would be the best choice. However, I am in the market to purchase TWO monitors. This is so I can view two programs simultaneously or when a client comes over, rotate the second monitor for their viewing. I mostly stare at numbers, words and Internet images. Also, I prefer larger monitors (i.e. 19"+). Should I consider two CRTs, CRT as my primary and LCD as the secondary, or match monitors and save real estate with two LCDs? What models would you recommend?
Your suggestions are appreciated.
Michael
Anonymous User - Saturday, September 13, 2003 - link
Also, it seems that marketing is mostly centered on inches instead resolution. A bit too often this is also true for reviews which tend to place things like elegance of design, or number of USB ports or some such, above petty details like displayable desktop area.Is this just some braindead carryover from CRTs, or does the average consumer really not care about the number of pixels he gets?
Anonymous User - Friday, September 12, 2003 - link
One thing I'd like to know is why is that usual native resultion for 19" LCDs 1280x1024? Or more specifically, why do 17" and 19" LCDs generally have the same native resolution.I would have thought that the logical progression would have been (based on the resultions usually used on equivalent sized CRTs):
15" 1024x768
17" 1280x1024
19" 1600x1200
But no, you generally have to go up to 21" LCD to get a 1600x1200 native resolution. And it can't be a technical problem, because we have 15" notebook LCDs with 1600x1200 (and higher) resolution.
So, does anyone know why the LCD industry made the bonehead decision to standardize on having 17" and 19" LCDs have the same native resolution?
PS. And don't bother pointing out that there are a few 1600x1200 19" LCDs. I'm aware of these exceptions. I just don't understand why this isn't the standard.
rapsac - Thursday, September 11, 2003 - link
#58That is anybody's guess. No way to find out unless you buy one and open it up. Then use the panel# to get the specs at the panel manufacturer. (And wave your warranty goodbye like I did mine :( )
joramo - Tuesday, September 9, 2003 - link
Are this 16.7m color specifications true or is the same 18 bits AUO panel?ACER AL732 - 17"
Technical specifications
Display size 17"
Display type Active color matrix TFT
Display area 338 x 270 mm
Brightness 260 cd/m²
Resolution 1280 x 1024 pixels
Colour 16.7m (8-bits per color)
Pixel pitch 0.264 (H) X 0.264 (W)
Contrast ratio 450:1
Response rates Total: 16ms
Thx
KristopherKubicki - Monday, September 8, 2003 - link
#55: on the contrary, lg.philips actually informed us of the opposite. While technically the dithering does not impact the response time, electrical modulation does. This is a direct result of how many bits the signal is capable of.Kristopher
Anonymous User - Monday, September 8, 2003 - link
Are there any formal reviews on new substrates that offer 10-bit gamma correction? In particular, I am considering either the Sharp T1820 or the EIZO L695 (L685EX), and considering that their specs are fairly similar, I assume they are using the same substrate. Supposedly the 10-bit gamma correction is capable of displaying a 1024-step greyscale, which can help prevent banding in subtle gradiants.Unfortunately, neither of these LCDs are widely available for me to perform my own eye-testing. Ideally if someone can offer advice on whether this is an overpriced two-step-conversion technology (as with using an analog cable on an LCD), or if this truly offers discernable benifits, that would be great!
The Sharp T1820:
http://www.sharpsystems.com/tmplproduct_T1820.asp
The EIZO L695:
http://www.eizo.com/products/lcd/l695/contents.htm...
Also worth noting, EIZO CG18
http://www.eizo.com/products/lcd/cg18/contents.htm...
Please email: fhsieh@exeter.edu
Any information is appreciated!
Anonymous User - Monday, September 8, 2003 - link
ALL TN+film panels use dithering (or Frame Rate Control as they call it) to interpolate 24 bits colors with a 18 bits signal. These panels are either quoted as 262K colors (64³) or 16.2 millions colors (253³). This applies to ALL 15" monitors and almost ALL 17" monitors (including the Samsung model quoted as 16.7 millions in the article). However all 18" and higher monitors use panel driven with a 24 bits value.BTW, dithering has absolutely no impact on response time.
Anonymous User - Sunday, September 7, 2003 - link
Info on the Samsung X line fo monitors, in case anyone is interested.http://monitor.samsung.de/detail_tft_syncmaster.as...