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Liquid crystal display technology works by blocking light. Specifically, an LCD is made of two pieces of polarized glass (also called substrate) that contain a liquid crystal material between them. A backlight creates light that passes through the first substrate. At the same time, electrical currents cause the liquid crystal molecules to align to allow varying levels of light to pass through to the second substrate and create the colors and images that you see.
Active and Passive Matrix Displays
Most LCD displays use active matrix technology. A thin film transistor (TFT) arranges tiny transistors and capacitors in a matrix on the glass of the display. To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge until the next refresh cycle.
The other type of LCD technology is passive matrix. This type of LCD display uses a grid of conductive metal to charge each pixel. Although they are less expensive to produce, passive matrix office monitors are rarely used today due to the technology's slow response time and imprecise voltage control compared to active matrix technology.
LCD displays offer super sharp pictures and great color. But do the pros outweigh the cons when it comes to LCD TV displays? Before deciding on a thumbs up or thumbs down, you should understand how an LCD display works.
Mechanics of an LCD display
The LCD consists of a large number of pixels, or picture elements, consisting of liquid crystal molecules held between two sets of transparent electrodes.
The liquid crystals react in predictable ways when the electrical charge running between those electrodes is changed — meaning they twist and move in ways that let different amounts (and colors) of light through the crystals. The LCD has a control system that translates your video signals into the proper charges for each electrode. A light source shines through the LCD panel and creates your picture.
When compared to the other type of flat-panel display (plasma), LCDs tend to be found on the smaller size of the spectrum. You’ll rarely find a plasma smart TV smaller than 42 inches, but you can find LCDs at sizes as small as 13 inches.
Benefits of LCD displays
LCD displays have some strong points when it comes to playing video:
Extremely high resolutions: LCDs can easily reach HDTV resolutions (in fact, most LCD displays do). You can find a 1080p-capable LCD display in all but the smallest sizes — while many plasma displays are still 720p.
Excellent color: LCDs offer exceptional reproduction of colors, with the potential for beautifully re-created colors across the spectrum. This differs from other flat-panel displays (such as plasma systems), which often tend to display certain colors inaccurately.
Great picture: The newest and most expensive LCDs use an LED (light emitting diode) instead of a traditional bulb for their light source. These LEDs produce a higher-quality picture because the LED itself emits a more natural (closer to daylight) light than a bulb (which tends to be yellowish, not true white).
Energy efficiency: LCD HDTVs are perhaps the greenest HDTVs. Compared to plasmas, LCD HDTVs use less electricity to run. You can probably expect to use about 30 percent less power for an LCD than for a similar-sized plasma.
PC monitor-capable: Most LCD television displays can also do double-duty as a gaming monitor, plugging directly into any PC with a standard PC video cable.
No burn-in: If you play a lot of video games, watch the stock ticker on MSNBC, or do other things with your display that involve a lot of static content (images that don’t change or move around) on a CRT display, you can end up with those images permanently burned into the phosphors on your LCD screen. Because LCDs use a separate backlight instead of creating their own light with phosphors, they are immune to this problem (plasmas are not, by the way).
Inherently progressive: Unlike direct-view systems, LCDs don’t display their picture using electron guns scanning lines across a screen. Instead, LCDs use millions of tiny transistors that can be individually controlled by the “brains” inside the display. This means that LCDs can easily handle progressive-scan sources, such as progressive-scan DVD and HDTV.
Drawbacks of LCD displays
Consider the following problem areas before you buy an LCD system as your primary display in a home theater:
Slightly more expensive for their size: Inch for viewing inch, LCDs tend to be a bit more expensive than plasma flat-panels.
Poor reproduction of blacks: Compared with direct-view tube displays, LCDs do a poor job of reproducing black images. Darker screen images never show up as true black, but rather as various shades of gray, and actions happening in these darker areas are difficult to discern.
Limited viewing angle: Although they are getting better due to some intensive efforts by manufacturers, LCDs typically have a poor viewing angle. If you are not sitting almost directly in front of the screen, such as 21.5 inch screen pc, or 24 inch screen pc, you don’t get a good picture.
Limited brightness: Because LCDs use a backlight shining through the liquid crystal, most of the light is absorbed. As a result, the LCD displays have lower contrast and are harder to view in a brightly lit room (the picture appears washed out), compared with plasma TVs. LCD TVs with LED backlights do better in this regard.
LED vs. LCD TVs explained: What’s the difference?
Despite having a different acronym, LED TV is just a specific type of LCD TV, which uses a liquid crystal display (LCD) panel to control where light is displayed on your screen. These panels are typically composed of two sheets of polarizing material with a liquid crystal solution between them. When an electric current passes through the liquid, it causes the crystals to align, so that light can (or can’t) pass through. Think of it as a shutter, either allowing light to pass through or blocking it out.
Since both LED and LCD TVs are based around LCD technology, the question remains: what is the difference? Actually, it’s about what the difference was. Older LCD TVs used cold cathode fluorescent lamps (CCFLs) to provide lighting, whereas LED LCD TVs used an array of smaller, more efficient light-emitting diodes (LEDs) to illuminate the screen.
Since the technology is better, all LCD TVs now use LED lights and are colloquially considered LED TVs. For those interested, we’ll go deeper into backlighting below, or you can move onto the Local Dimming section.
Three basic illumination forms have been used in LCD TVs: CCFL backlighting, full-array LED backlighting, and LED edge lighting. Each of these illumination technologies is different from one another in important ways. Let’s dig into each.
CCFL backlighting is an older, now-abandoned form of display technology in which a series of cold cathode lamps sit across the inside of the TV behind the LCD. The lights illuminate the crystals fairly evenly, which means all regions of the picture will have similar brightness levels. This affects some aspects of picture quality, which we discuss in more detail below. Since CCFLs are larger than LED arrays, CCFL-based LCD TVs are thicker than LED-backlit LCD TVs.