Geek 101: LCD and Plasma Basics

LCD vs. Plasma

If you've gone shopping for a new PC or HDTV, you've probably seen a dizzying array of display-technology terms bandied about in the fine-print specs listings on store shelves. You may have asked yourself, "What do these terms mean? Does any of it really matter?" We hear you. Here's our no-nonsense guide to what these specs mean, what you need to know about them, and what you should be looking out for.

LCD and plasma are the most common types of displays you'll see on the market. Plasma is predominantly used for HDTVs, while LCDs are common in both TVs and computer monitors. Several other interesting technologies are on the horizon, as well.

Some of the most important factors contributing to a display's quality are its color depth (how accurately the screen can reproduce colors), its viewing angle (whether any color shifting occurs when you view the screen from the sides), and its motion processing (how well the screen can handle fast-action scenes). We'll look at all of those topics in this primer.

Plasma vs. LCD

Until fairly recently, plasma was the preferred technology for HDTVs; it has since been overtaken by LCD. Plasma technology has several advantages and disadvantages in comparison to LCD.

Plasma sets have claimed a smaller percentage of HDTV sales lately. Some vendors, such as Samsung and Panasonic, make both LCD and plasma HDTVs, but most manufacturers have ditched plasma technology. Pioneer discontinued its plasma HDTV line last year.

The biggest drawback to plasma is its power usage. Plasma HDTVs generally consume more power than comparable LCD TVs do, which of course means that you'll have to pay more on your electric bill with a plasma model than with an LCD set. Plasmas are also more susceptible to screen burn-in and image ghosting than LCDs are, although that is less of a problem with current plasmas than it was with older models.

That said, there are real reasons to consider buying a plasma instead of an LCD, especially if you value image quality. Plasma displays do a much better job of handling dark scenes, and they have better viewing angles than most LCDs do. Plasma HDTVs have historically handled fast motion more smoothly than LCDs have, too. In fact, it hasn't been until the past couple of years--with the advent of LED backlighting and faster refresh rates--that LCDs have become competitve with plasmas in this respect.

LCD: Liquid Crystal Display

Liquid crystal display--LCD for short--is one of the most common screen types you'll find in a PC or TV.

LCD screens employ several different technologies, with twisted nematic (TN) and in-plane switching (IPS) being a couple of the most prevalent. Other higher-end LCD types include MVA (Multi-domain Vertical Alignment) and PVA (Patterned Vertical Alignment).

The differences among the display types tend to be arcane (having to do with how the liquid crystals inside the displays are structured), but there is one key difference that most people should care about: A TN LCD panel will generally have narrower viewing angles than an equivalent IPS, MVA, or PVA panel. Wider viewing angles mean less color shifting when you look at the screen from the side. HDTVs normally use the higher-performing IPS, MVA, and PVA technologies.

Color Depth

Some LCDs are 6-bit panels, which are capable of displaying approximately 65,000 colors; others are 8-bit, and can display over 16 million colors. On the very high end, there are 10-bit LCDs that can display over a billion colors. A 6-bit LCD can mimic 8-bit color to some extent by using a technique called "dithering." This approach tries to approximate the true color of an image by using combinations of colors that the screen is capable of displaying.

For most computer users, a 6-bit display may not be ideal, but if all you're doing is Web browsing and word processing, it isn't the end of the world. On the other hand, if your work requires high color accuracy--professional photo or video editing, for example--you'll want to make sure that you get at least an 8-bit screen. HDTVs normally use 8-bit or better screens, so this is less of a concern for HDTVs.

Backlighting

The other big differentiator among LCDs is the backlight. Traditionally, LCDs used a cold-cathode fluorescent lamp (CCFL) backlight, a setup that basically uses a fluorescent tube to illuminate your screen. The biggest drawback to CCFLs is that over time the backlight dims somewhat, so as your HDTV or computer monitor ages, it'll become darker and less vibrant.

LED (light-emitting diode) backlighting fixes that particular issue, and offers some added benefits. LED backlighting won't dim as it ages; and unlike CCFL backlighting, which takes a few moments to warm up to full brightness when you turn on the screen, LED backlighting is at its full brightness from the moment you switch it on. LED backlighting is also more energy efficient, making it ideal for laptops and other portable devices such as smartphones or tablets. Market research firm DisplaySearch predicts that over half of the HDTVs sold in 2011 will ship with some form of LED backlighting.

You can find two variations of LED backlighting. Edge-lit LED backlighting, as its name suggests, places the LEDs along the edge of the display, whereas in full-array LED backlighting, the LEDs sit behind the panel itself. Typically, full-array LED backlighting can do a useful additional trick: It can turn off the backlight in darker areas of a scene to improve the display's contrast--a technique known as local-area dimming.

That said, local-area dimming is coming to some edge-lit LCDs as well. At this year's Consumer Electronics Show, Samsung announced edge-lit LED-backlit HDTVs that also have the local-area dimming function.

Next: Refresh rates, contrast ratios, 3D, and OLED

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