Plasma, Rear Projection, and LCD Displays Change TV Forever

Since its invention decades ago, there have been constant advances in television manufacturing.  One thing has remained constant: the Cathode Ray Tube that projects images onto the television screen.  Now the television industry is experiencing a paradigm shift that promises to eliminate these traditional television sets by replacing them with flat panel technology. Plasma and LCD televisions and monitors provide breathtaking imagery and vibrant color. They also take up less space than ordinary televisions.  The recent decline in price has catapulted the flat panel industry from designer chic to an emerging television standard.

Cathode ray tube television sets (often called CRT televisions for short) consist of a sealed tube where an electron gun at one end of the tube fires a beam of electrons at the other end, which is coated in phosphors.  These phosphors light up on the wide end (this end serves as the television screen) illuminating pixels and creating an image. The bigger the desired display, the larger (and deeper) the television must be.  Flat panel television technology can produce astoundingly better imagery and color for a fraction of the size and almost half the weight.

Why is the traditional CRT television on the endangered list?

Flat panel displays like plasma and LCDs monitors are brighter and have incredible color contrast compared to CRTs.  Lighting conditions don’t affect the output quality as much as CRTs.  Flat panel technology is the only display capable of doing justice to increasingly popular High Definition television and other media.

Ooh, fancy.  But what is plasma?

Plasma is a gas made up of free-flowing ions and spare electrons.  Under natural conditions any particular gas is mostly composed of uncharged particles.  This means that within individual gas atoms the number of protons (positively charged atomic particles) and electrons (negatively charged atomic particles) is equal. Running an electric current through a gas in confined space introduces free electrons to the gas.  These free electrons collide with individual gas atoms, knocking other electrons within those atoms loose.  This creates ions (atoms with positive electrical charges) within the gas.

When electric current passes through plasma, it causes these gas ions and free electrons to rush towards oppositely charged (and oppositely positioned) ends of the plasma.  As they pass each other, they collide.  These collisions excite the gas atoms, causing them to release tiny amounts of energy called photons.

To create a visible effect, the plasma is contained in tiny, sealed cells.  Each cell is coated in a substance called a phosphor.  Phosphors give off one kind of light if they are exposed to another kind of light.  The phosphors employed in plasma televisions emit visible light when exposed  (in this case, exposed means bombarded by) to ultraviolet light.  In plasma televisions, the phosphors produce light in three primary colors: red, green and blue. A primary color is one of the three colors that make up every hue in the visible spectrum of light. Three of these different phosphor-coated cells make up a single pixel on a plasma television display, and a plasma television display is made up of hundreds of thousands of pixels.

A plasma television picture is achieved by sandwiching thousands of plasma-filled cells between two pieces of glass along with two sets of electrodes, one on either side of the plasma cells.  The television display computer releases specific electrical currents, each one going to a different cell.  Varying the current alters the amount of light released by each phosphor.  The display computer accomplishes this task thousands of times in a fraction of a second. This creates the vibrant images on the screen.

Ah.  Do LCD televisions and monitors work the same way?

The short answer is no. LCD televisions and monitors produce comparable image quality and in many ways are a more versatile technology than plasma televisions.  The “LCD” in LCD televisions and monitors stands for “Liquid crystal display”.  Liquid Crystal Displays are not new.  Not everyone knows what it means, or how it works.

Liquid crystals are tiny rod shaped molecules that can be manipulated with electric current.  Liquid crystals become opaque when fully “untwisted”. When liquid crystals are exposed to electrical current, they will twist tighter or unravel.  Varying the amount of electrical voltage alters the degree to which these crystals unravel. This changes the intensity of light passing through.

An LCD flat panel display manipulates the amount and intensity of light that passes through the pixels by sandwiching a solution of these liquid crystals between two polarized pieces of glass. They are placed behind a colored filter layer and in front of a layer of diodes and transistors. This electrode layer delivers commands from the display computer that indicate which crystals should untwist and which should curl.

An active LCD matrix has thousands of tiny segments called pixels (this is the color filter layer) that form images and project information on the screen.  These pixels are actually color filters. They block all but their own color spectrums of light. These pixels are broken down into sub-pixel sets, each consisting of three primary colors: red, green, and blue. Each pixel contains one of these three colors, and each display contains hundreds of thousands of pixels.

It is important to realize that liquid crystals do not create light in and of themselves.  They simply act as a filter for another light source.  That light source in LCD televisions and monitors is a fluorescent bulb. This bulb projects white light through the polarized glass pane that sits behind the liquid crystals.  This gives liquid crystal displays vibrant colors and crisp, distinct images.

What is the difference between LCD televisions and so-called Rear Projection televisions?

Rear Projection Televisions have made huge advances in technology as well.  One example of that emerging science is DLP televisions.  DLP televisions cost less as a rule and currently are available in sizes larger than most LCD televisions in production.  The reason has to do with basic mechanics: LCD television and DLP television technologies differ greatly in how the image is generated.  It is important to understand what DLP is and how it works before deciding between rear projection and LCD.

DLP is a revolutionary design that uses an optical semiconductor to digitally manipulate light. At the heart of a DLP projection system is an optical semiconductor known as the Digital Micromirror Device, or DLP chip.  It contains a rectangular array of up to 2 million hinge-mounted microscopic mirrors. Each one measures less than one-fifth of a human hair.

Its mirrors reflect an all-digital image onto a screen.  The chip’s tiny mirrors are mounted on miniscule hinges that enable them to tilt toward the light (ON) or away from it (OFF).  This makes the screen show either a light or a dark pixel. When a mirror is switched on more often, it reflects a light gray pixel. When the mirror is switched off more frequently it reflects a dark gray pixel.

Colors are produced by filtering light from a lamp through a color wheel on its way to the mirrors. The color wheel filters the light into the primary colors red, green, and blue. A single-chip DLP projection system to create at least 16.7 million colors.  Not every brand or model of rear projection television features DLP.  Some brands use other technologies.  Read all available features of a particular product before buying.

There are quite a few new terms associated with flat panel display televisions.  What do they all mean?

Understanding the terminology of the LCD and plasma display television industry is key to making an informed purchase.  Here are a few explanations for some of the jargon you may encounter when buying a flat panel display.

Resolution: It’s important to know exactly what the resolution specs on any particular television indicate.  The resolution is usually given as one number by another number (ex: 1920×1080) and is sometimes followed by a letter, either I or P.  These letters indicate a specific type of input signal.  The two number values refer to the number of pixels the screen contains. The first number indicates how many pixels run from left to right along the horizontal edge of the screen.  The second number indicates how many pixels run from top to bottom along the vertical edge of the screen.  The second number is the most important. It determines whether the display can be classified as High Definition.

High Definition:  In order for a television to be classified as “High Definition” (more commonly referred to as HDTV) it must have at least 720 pixel rows along the vertical edge of the screen.  The highest definition televisions have 1080 vertical pixel counts, or 1080 individual rows of pixels along the vertical edge of the display screen.  These HD televisions are sometimes referred to as 1080p or 720p sets.  They produce stunning images with impeccable clarity, crisp movement, and distinct, vibrant colors.  Only 1080p HDTVs can display all the detail in 1080i signals of HDTV broadcasts or the 1080p signal delivered from players such as HD-DVD and Blu-Ray.

Interlaced vs. Progressive-scan

High Definition signals (as well as standard and so-called “enhanced” definition signals) are identified by a numerical value that is often followed by a letter.  Take “High Definition” broadcasts as an example: some HDTV transmissions are dubbed 1080i and some televisions are referred to as 1080p or 720p. The numbers indicate the lines of data contained in the signal; the letters refer to how the data is delivered.

Interlaced:  An “I” indicates that the signal is interlaced; this means that the pixel data arrives in two fields only a fraction of a second apart.  Half the pixel information required for an image is sent first, the other half second.  A viewer will perceive these two fields as a single frame.

Progressive Scan:  A “P” indicates that the signal is progressive-scan.  This means that all the pixel data for a single frame is both captured and transmitted in a single sweep.  Because interlaced images contain two fields of information at the same time, some flat panel displays will suffer blurring on the edges of moving objects.  Progressive-scan televisions and signals greatly reduce this problem.  Because the data is projected simultaneously, the image appears smoother.

Aspect Ratio:  An aspect ratio is the ratio of the width of the image to the height of the image.  HDTV is broadcast in a 16:9 aspect ratio.  A “normal” television generally comes in a 4:3 aspect ratio.  Watching standard television broadcasts on a 16:9 aspect ratio television does not mean distorted images, however.  Most sets have at least two options: they can either display the data in standard 4:3 aspect ratio (usually with black or gray bars framing the image) or employ specific algorithms to stretch the image without altering it.  It is important to note that the future of television and broadcasting probably lies with HDTV aspect ratios. I would recommend buying a flat panel display television capable of 16:9 aspect ratio.

HDMI:  HDMI is the newest form of input connection for flat panel display televisions.  It allows a digital signal to remain digital.  HDMI is a slim, single cable connection that also carries audio input with minimal degradation.  It is the heir apparent to DVI, a video-only cable that is commonly used to connect a flat panel display for use as a computer monitor.  Most LCD or Plasma display televisions have one HDMI port. Some are equipped with more. This offers better communication with components that support the connection.

How do I choose between LCD and plasma flat panel displays?

This is a tough question, and there is no simple answer.  The original obstacles that plagued flat panel technology in the past have been virtually eliminated. Consider what you intend to do with the flat panel display.  You should also have a clear idea of what expectations and standards you desire.  Here are some of the pros and cons regarding Plasma and LCD display televisions.

Plasma Display Pros:

  • Many Plasma televisions produce richer, more vibrant hues and deeper inky blacks than LCD displays.
  • Fear factors like “burn-in” and screen glare have been largely eliminated.  When a plasma display heats up, it can “burn” an after effect of an on-screen image into the pixel phosphors.  New models of Plasma television have features that help to minimize burn-in. Combining these new features with simple responsibility on the consumer’s part keeps these phantoms from appearing.
  • There is no limit to the angle at which you can view a Plasma screen television.  LCD displays tend to distort when viewed from an angle. This makes it imperative to stay relatively in front of the screen.  Newer, high-end LCD displays have virtually eliminated this problem.

Plasma Display Cons:

  • One thing that still holds true is this: Plasma televisions require a large field of space for their pixel arrays. This prevents plasma display televisions from being offered in sizes smaller than about 40 inches.  They are often heavier than LCD televisions, when compared to a model of similar size.
  • Plasma televisions tend to have lower pixel counts than LCDs, which leads to visible pixel structure and difficulty reproducing gradations between subtle shading. Newer high-quality models virtually eliminate this distinction.

LCD Display Pros:

  • LCDs are the lightest and most versatile of the two flat panel technologies.  LCDs that are of comparable size to plasma displays weigh less; they also generate less heat and therefore are more desirable for applications where space and ventilation are hard to find.
  • LCDs come in a much wider variety of sizes; the restrictions involved in plasma display televisions prevent them from being produced much smaller than 40 inches.
  • LCD displays are ideal for computer applications because higher resolutions make them perfect for gaming, graphics, and other computing tasks.
  • The advent of LCD display televisions with 1080p resolutions promise to provide astounding image quality.

LCD Display Cons:

  • The angle at which an LCD screen can be viewed is less than that of Plasma televisions.  Higher end LCD flat panels have significantly reduced this drawback, but it still exists.
  • LCDs have difficulty producing the same vibrant colors and deep, inky blacks of plasma televisions.  Higher end LCDs have made serious strides to correct this problem, but it still exists in more affordable models.
  • LCDs with slower refresh times (a refresh time refers to the time it takes for an LCD pixel to switch on and then off again) experience “streaking” or “trailing”.  LCDs can also suffer from “ghosting”, a term used to describe after-images left over when the screen changes abruptly from a dark image to a lighter one.

The Final Decision

No matter what flat panel technology you choose, take your own desires into consideration first.  Are you a sports fanatic?  Higher HD resolutions in LCDs and rear projection displays are perfect for keeping tabs on instant replays!  Are you a movie buff?  Plasma displays create vivid colors and inky blacks like no other.  Do colors matter most to you? Or is it precision graphics and imagery?  Will you be filling the largest wall in your living room, or simply installing your flat panel on the kitchen counter to watch while cooking or for company during dinner?

The flat panel display industry is ready for you, no matter what your application or budget.  Join the hundreds of thousands of viewers that now experience their TV programs, movies, and sports broadcasts in amazing picture clarity and precise attention to detail.  Ditch your CRT television, or keep it as a memento to good times past.  It’s time to awe the family and impress the neighbors with your new high-tech living room and your knowledge of flat panel display televisions!

Related Links: LCD TV (25″ or less), LCD TV (26″ or more), Plasma TV (43″ or less), Plasma TV (46″ or more), Rear Projection Television, DLP Television