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Display Details And LCD Panel Types

Display Power Consumption: CRTs Versus TFT-LCDs
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There's no point in stretching out a CRT discussion, since these are largely obsolete. Suffice it to say that cathode ray tube designs use an electron gun that draws images onto a fluorescent screen, line by line. At refresh rate of at least 75 Hz is desirable for a flicker-free image; 85 Hz or more is better. CRTs are housed in glass envelopes, making them physically deep, heavy, fragile, and susceptible to magnetic interference. They're also environmentally unfriendly, owing to various toxic coatings. High-frequency noise, possible implosion (it’s a vacuum tube), and some radiation also don't help curry favor when comparing to LCD technology. CRTs do have some advantages, but they are overshadowed nowadays.

Unlike CRT displays, every LCD has a native resolution at which it should operate for optimal image quality. Setting a native 1920x1080 display to only 1600x900 results in blurry images, as the output resolution has to be converted to the physical resolution. For best quality results, use digital connections to LCDs, such as DVI, HDMI, and DisplayPort. Avoid the old, analog 15-pin D-Sub connections that converted digital output into an analog signal for transmission, then re-digitize it for display on your LCD monitor. Such conversions always result in image quality loss that can be avoided by a digital link.

Most modern LCD monitors are based on active matrix thin-film transistor (TFT) technology. These displays are based on a TFT array substrate containing transistors, capacitors, wiring, and pixel electrodes, which serve to apply voltage between the TFT substrate and the color filter substrate, which contains red, green, and blue sub-pixels. The two glass substrates are kept apart by spacers and cells filled with liquid crystal material. The outer faces of the TFT panel are equipped with polarizing sheets. Finally, data lines attach to LCD driver chips. Each pixel can be addressed separately in this matrix through the bonding pads at the end of each row and column, as if the monitor were lighting up pixels by playing Battleship.

LCD Panel Types

There are significant differences in performance and characteristics between one LCD display and the next. As with most technologies, you can generally assume that newer products are superior (of course, this isn't always the case). Details like response time and input lag (the time required to change a pixel’s color and to have an input signal change the display, respectively), viewing angle, brightness, and contrast improve from one generation to the next.

Twisted nematic (TN) panels are the most widespread TFT type, offering response times of only a few milliseconds (though response time varies between different color transitions). Contrast, viewing angle, and color reproduction remain issues, especially with low-cost TN devices. Color reproduction can be problematic for image processing or other professional applications, given that each color is typically represented by only six bits, resulting in 18 bits as opposed to the 24-bit color necessary for 16.7 million true colors.

In-plane switching (IPS) panels have the liquid crystals in parallel to the panel, not perpendicular to it. Viewing angles are much wider, and light scatters much less within the matrix, which is why color reproduction can be more precise. Initially, this precision came at the expense of response time. Advanced Super-IPS (AS-IPS) provides an improved contrast ratio, and Horizontal-IPS (H-IPS) works on professional LCDs for a more natural white color. Enhanced-IPS (E-IPS) is more advanced still, bringing response time back to only a few milliseconds, but it’s much more expensive than a TN panel.

Multi-domain vertical alignment (MVA) panels are a compromise between TN and IPS. Colors don’t change as much if you move away from a perfect 90° relative to the monitor's screen plane. Color reproduction and response time are good, too. Patterned vertical alignment (PVA) is a similar technology with higher contrast. S-PVA is considered the most advanced technology of the group, utilizing more than eight bits per color, showing the deepest blacks, and offering the quickest response times.

Recently, conventional fluorescent backlights are being replaced by white LEDs. These typically last longer and consume less power, which is the main motivation for our analysis. Do LEDs really make that much of a difference? Let's find out.

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  • 30 Hide
    Anonymous , August 19, 2010 8:32 AM
    Although this is a useful article, I think your advice about ditching CRTs is misguided. Just because a new LCD uses less electricity doesn't mean it is automatically more environmentally friendly. You have to consider the environmental impacts of the production of the monitor.

    If you use your monitor 6 hours a day, it would take ~10 years for the savings in electricity consumption to offset the initial cost of a new LCD. It would likely take at least as long to offset the environmental impact of the production of that LCD (I don't feel like running a life cycle analysis for a comment but this is usually the case).

    There are many reasons to switch to an LCD, but saving the environment shouldn't be one of them. The best thing for the environment is to use what you already have until it's worn out.
  • 18 Hide
    mikewong , August 19, 2010 7:13 AM
    Ah! Haven't seen a monitor review from Tom since a long time.
    This is not really a review but it's better than nothing.
    Thanks Tom!
  • 14 Hide
    vjineo , August 19, 2010 12:18 PM
    welanand The best thing for the environment is to use what you already have until it's worn out.


    Couldn't have said it better.
Other Comments
  • -6 Hide
    Hupiscratch , August 19, 2010 6:25 AM
    I´m currently operating my SyncMaster 2493HM at just 10% brightness and is looking great. It can even diminish heat emissions from the screen to your face.
  • 14 Hide
    Scanlia , August 19, 2010 6:35 AM
    CRT's have a nice and high screen refresh rate, good for playing old games.
  • 13 Hide
    beans4you , August 19, 2010 6:36 AM
    brightness reduction can save you power consumption yes. I also like the idea of web designers using black backgrounds, its a fact that white backgrounds (like toms >.>) require your monitor to use more power than dark. :D 
  • 18 Hide
    mikewong , August 19, 2010 7:13 AM
    Ah! Haven't seen a monitor review from Tom since a long time.
    This is not really a review but it's better than nothing.
    Thanks Tom!
  • 12 Hide
    stewartwb , August 19, 2010 7:14 AM
    I'm not sure that a white background matters much for LCD monitor power consumption, except for HDTVs with a matrix of LEDs that get turned off behind black areas. Normally, the backlight is turned on to whatever brightness level the user selects, then the LCD panel selective filters (blocks) that white light to make various colors. If anything, showing a solid-black screen image would require slightly more electricity to force those pixels dark (pure white would require no electricity for the pixels, since it's blocking nothing). Also, a solid-black picture would absorb all of the backlight, which would convert that light to heat inside the monitor rather than allowing the light to escape.

    From the article, I assume the power required by the backlight trumps the power required to drive the LCD filter portion of the monitor.
  • 9 Hide
    zelog , August 19, 2010 7:15 AM
    But you can't beat CRT for movies or gaming, there's just so much more detail. Gaming Example: With LCD, experienced people will notice someone hiding in the shadows because they see "something" that usually isn't there. A CRT monitor will show the whole person fully visible, because the CRT handles the darker shades on dark backgrounds much better. Or maybe I just need to get a newer LCD.
  • 30 Hide
    Anonymous , August 19, 2010 8:32 AM
    Although this is a useful article, I think your advice about ditching CRTs is misguided. Just because a new LCD uses less electricity doesn't mean it is automatically more environmentally friendly. You have to consider the environmental impacts of the production of the monitor.

    If you use your monitor 6 hours a day, it would take ~10 years for the savings in electricity consumption to offset the initial cost of a new LCD. It would likely take at least as long to offset the environmental impact of the production of that LCD (I don't feel like running a life cycle analysis for a comment but this is usually the case).

    There are many reasons to switch to an LCD, but saving the environment shouldn't be one of them. The best thing for the environment is to use what you already have until it's worn out.
  • 9 Hide
    belardo , August 19, 2010 8:42 AM
    My previous monitor was a semi-pro Samsung 19" CRT, which I ran at 1600x1200. It was huge, heavy and was glad to get rid of it... but I needed an LCD that was JUST as high and res and affordable.

    As Zelog says about some advantages of CRT... sure, if comparing to LCDs made before 2008... the "ripping" effect can be easily fixed and very rare nowadays. One of the reasons I didn't want an LCD is that some games had to run on various resolutions... which would look like crap. But even with my trusty slow ATI 4670, I play almost ALL games in 1920x1200 on my Samsung 24" 245B (like in this review) which I bought in 2008.

    I'd never go back to a CRT... the text is never PIXEL crisp. My eyes are not hurting anymore. As my monitor aged, it developed issues and sometimes noise... also my son scratched OFF some of the anti-glare coating on my CRT and it was bugging me. I waited until he got a bit older before I replaced it. ;) 

    Oh, same kid (at age 3+) had a 19" 4:3 Dell LCD I got for $50. It recently died (meanwhile, my 1999 Samsung 15" LCD still works for tech work), so I bought a $110 ASUS 20" wide-screen LCD with LED back lighting. I don't like todays extra-wide screen displays, but this younger monitor easily has a better picture than my Samsung... but I ain't down-grading on size or resolution ;) 


    What I want in 2~3 years from now... is something like an iphone-rez desktop monitor.
    That is about 26" wide, but has a resolution of 3200x2000. Imagine how sharp and awesome that would be... retina display. *I* BET Apple will be doing that with their computers soon. Seeing the pixels is the next thing to go.

    PS: Death to glossy LCD displays!
  • 13 Hide
    Anonymous , August 19, 2010 8:50 AM
    Oh how I miss 85 hz!!!!
  • 13 Hide
    Transsive , August 19, 2010 8:57 AM
    LCDs have so many shortcomings
    - blur/ghosting (very important for games, not that bad with 120Hz)
    - most only handle 60Hz (60 fps in games)
    - viewing angles (horrible with TN)
    - color changes it's brightness across the screen surface (again TN)
    - backlight bleeding
    - horrible blacks
    - some LCDs buzz
    - some have input lag issues

    Other cons might include: only one native resolution, dead or stuck pixels, lack of aspect ratio control

    What's good about LCDs?
    - HD resolutions
    - power consumption
    - thickness and weight
    - design
    - less eye strain (no flicker, although the blur gives me headaches)
    - possibly higher contrast ratios
    - digital connections

    And 1680x1050 is a 16:10 resolution...

    My next LCD will be an ISP 1920x1200 120Hz monitor... if they ever show up. I've had it with TN panels, too much image degrading, you buy a gaming rig to play at high details only to have the monitor waste it.
  • 6 Hide
    Minerva , August 19, 2010 9:14 AM
    Hmmm, I run a dual 19" setup at home, with CRT's ;) 

    I still haven't found an LCD monitor that I like :(  I don't like the heavy widescreen display, in fact, I still prefer 4:3. Also I collect Vintage computers, so 4:3 CRT fits in with them quite nicely. I can just imagine how cruddy 320x240 is going to look like on a 24" LCD.

    I don't know what the "bleeding" is like these days on LCD's as that used to be a huge issue on the older stuff.

    Come to think of it, the only LCD that I own is the one on my HP 6910p work laptop :? I have 2x 17" and 3x 19" and they are all CRT :D 
  • 0 Hide
    icepick314 , August 19, 2010 9:53 AM
    transsiveMy next LCD will be an ISP 1920x1200 120Hz monitor... if they ever show up. I've had it with TN panels, too much image degrading, you buy a gaming rig to play at high details only to have the monitor waste it.


    for those who are interested in ISP panels...

    http://www.pchardwarehelp.com/guides/s-ips-lcd-list.php

    unfortunately it doesn't show what refresh rate those monitors have....mostly likely 60Hz...
  • 1 Hide
    pertshire , August 19, 2010 10:08 AM
    Stupid question, when you said reducing the brightness to save power, are you talking about the back lighting level or the actual brightness level? I usually keep the backlighting low and brightness and contrast high thinking brightness has nothing to do with power.
  • 7 Hide
    helmutcheese , August 19, 2010 11:52 AM
    Sony FW900 F.T.W

    16:10 24" CRT (22.5" Viewable) Max 2304x1440 @ 85HZ

    Good for Nvidia 3D as it only needs be 100HZ on CRT or lower RES 1 notch and go for 1680x1050 @ 120HZ.

    Gaming at 1920x1200 100HZ with proper blacks and full colours and zero input lag with no need for V-Sync so no need to enable laggy Triple Buffering which affects Online MP Gaming.
  • 0 Hide
    nebun , August 19, 2010 12:14 PM
    transsiveLCDs have so many shortcomings- blur/ghosting (very important for games, not that bad with 120Hz)- most only handle 60Hz (60 fps in games)- viewing angles (horrible with TN)- color changes it's brightness across the screen surface (again TN)- backlight bleeding- horrible blacks- some LCDs buzz- some have input lag issuesOther cons might include: only one native resolution, dead or stuck pixels, lack of aspect ratio controlWhat's good about LCDs?- HD resolutions- power consumption- thickness and weight- design- less eye strain (no flicker, although the blur gives me headaches)- possibly higher contrast ratios- digital connectionsAnd 1680x1050 is a 16:10 resolution...My next LCD will be an ISP 1920x1200 120Hz monitor... if they ever show up. I've had it with TN panels, too much image degrading, you buy a gaming rig to play at high details only to have the monitor waste it.


    they have been out for years...look at dell and apple
  • 14 Hide
    vjineo , August 19, 2010 12:18 PM
    welanand The best thing for the environment is to use what you already have until it's worn out.


    Couldn't have said it better.
  • 1 Hide
    ihs97 , August 19, 2010 12:56 PM
    beans4youbrightness reduction can save you power consumption yes. I also like the idea of web designers using black backgrounds, its a fact that white backgrounds (like toms >.>) require your monitor to use more power than dark.


    True, but reading large walls of white text on black backgrounds is an eye-strain and a half.
  • 1 Hide
    gto127 , August 19, 2010 12:59 PM
    I'm currently using a Hitachi HM-4721D 21 inch monitor that I've been using since 1998. No blurriness all text is razor sharp. I have it on for about 5 or 6 hours a day since 98. It might save chump change to switch to a LCD but I wouldn't trade it for one.
  • 0 Hide
    Wolygon , August 19, 2010 1:07 PM
    beans4youbrightness reduction can save you power consumption yes. I also like the idea of web designers using black backgrounds, its a fact that white backgrounds (like toms >.>) require your monitor to use more power than dark.

    Not really for most monitors as they generally don't have the ability to shut off light to sections of the screen like Plasmas. Although for some of the new ones and LED backlits this applies.
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