Current and Future OLED Applications

Currently, OLEDs are used in small-screen devices such as cell phones, PDAs and digital cameras. In September 2004, Sony Corporation announced that it was beginning mass production of OLED screens for its CLIE PEG-VZ90 model of personal-entertainment handhelds.

Photo courtesy Sony Corporation OLED display for Sony Clie

Kodak already uses OLED displays in several of its digital-camera models.

Photo courtesy Shopping.com Kodak LS633 EasyShare with OLED display

Several companies have already built prototype computer monitors and large screen TVs. In May 2005, Samsung Electronics announced that it had developed the first 40-inch, OLED-based, ultra-slim TV.

Photo courtesy Samsung Electronics Samsung's prototype 40-inch OLED TV

Research and development in the field of OLEDs is proceeding rapidly and may lead to future applications in heads-up displays, automotive dashboards, billboard-type displays, home and office lighting and flexible displays. Because OLEDs refresh faster than LCDs -- almost 1,000 times faster -- a device with an OLED display could change information almost in real time. Video images could be much more realistic and constantly updated. The newspaper of the future might be an OLED display that refreshes with breaking news (think "Minority Report") -- and like a regular newspaper, you could fold it up when you're done reading it and stick it in your backpack or briefcase.

OLEDs pros and cons

OLED Advantages and Disadvantages

The LCD is currently the display of choice in small devices and is also popular in large-screen TVs. Regular LEDs often form the digits on digital clocks and other electronic devices. OLEDs offer many advantages over both LCDs and LEDs:

• The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystalline layers in an LED or LCD.

• Because the light-emitting layers of an OLED are lighter, the substrate of an OLED can be flexible instead of rigid. OLED substrates can be plastic rather than the glass used for LEDs and LCDs.

• OLEDs are brighter than LEDs. Because the organic layers of an OLED are much thinner than the corresponding inorganic crystal layers of an LED, the conductive and emissive layers of an OLED can be multi-layered. Also, LEDs and LCDs require glass for support, and glass absorbs some light. OLEDs do not require glass.

• OLEDs do not require backlighting like LCDs (see How LCDs Work). LCDs work by selectively blocking areas of the backlight to make the images that you see, while OLEDs generate light themselves. Because OLEDs do not require backlighting, they consume much less power than LCDs (most of the LCD power goes to the backlighting). This is especially important for battery-operated devices such as cell phones.

• OLEDs are easier to produce and can be made to larger sizes. Because OLEDs are essentially plastics, they can be made into large, thin sheets. It is much more difficult to grow and lay down so many liquid crystals.

• OLEDs have large fields of view, about 170 degrees. Because LCDs work by blocking light, they have an inherent viewing obstacle from certain angles. OLEDs produce their own light, so they have a much wider viewing range.

Problems with OLED
OLED seem to be the perfect technology for all types of displays, but they also have some problems:

• Lifetime - While red and green OLED films have long lifetimes (10,000 to 40,000 hours), blue organics currently have much shorter lifetimes (only about 1,000 hours).

• Manufacturing - Manufacturing processes are expensive right now.

• Water - Water can easily damage OLEDs.

Type of OLEDs

Types of OLEDs: Passive and Active Matrix

There are several types of OLEDs:

• Passive-matrix OLED
• Active-matrix OLED
• Transparent OLED
• Top-emitting OLED
• Foldable OLED
• White OLED

Each type has different uses. In the following sections, we'll discuss each type of OLED. Let's start with passive-matrix and active-matrix OLEDs.

Passive-matrix OLED (PMOLED)
PMOLEDs have strips of cathode, organic layers and strips of anode. The anode strips are arranged perpendicular to the cathode strips. The intersections of the cathode and anode make up the pixels where light is emitted. External circuitry applies current to selected strips of anode and cathode, determining which pixels get turned on and which pixels remain off. Again, the brightness of each pixel is proportional to the amount of applied current.

PMOLEDs are easy to make, but they consume more power than other types of OLED, mainly due to the power needed for the external circuitry. PMOLEDs are most efficient for text and icons and are best suited for small screens (2- to 3-inch diagonal) such as those you find in cell phones, PDAs and MP3 players. Even with the external circuitry, passive-matrix OLEDs consume less battery power than the LCDs that are currently used in these devices.

Active-matrix OLED (AMOLED)
AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer overlays a thin film transistor (TFT) array that forms a matrix. The TFT array itself is the circuitry that determines which pixels get turned on to form an image.

AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than external circuitry, so they are efficient for large displays. AMOLEDs also have faster refresh rates suitable for video. The best uses for AMOLEDs are computer monitors, large screen TVs and electronic signs or billboards.

OLEDs Emit Light

How do OLEDs Emit Light?

OLEDs emit light in a similar manner to LEDs, through a process called electrophosphorescence.

The process is as follows:

1. The battery or power supply of the device containing the OLED applies a voltage across the OLED.
2. An electrical current flows from the cathode to the anode through the organic layers (an electrical current is a flow of electrons).
   • The cathode gives electrons to the emissive layer of organic molecules.
   • The anode removes electrons from the conductive layer of organic molecules. (This is the equivalent to giving electron holes to the conductive layer.)
3. At the boundary between the emissive and the conductive layers, electrons find electron holes.
   • When an electron finds an electron hole, the electron fills the hole (it falls into an energy level of the atom that's missing an electron).
   • When this happens, the electron gives up energy in the form of a photon of light (see How Light Works).
4. The OLED emits light.
5. The color of the light depends on the type of organic molecule in the emissive layer. Manufacturers place several types of organic films on the same OLED to make color displays.
6. The intensity or brightness of the light depends on the amount of electrical current applied. The more current, the brighter the light.

Small Molecule OLED vs. Polymer OLED The types of molecules used by Kodak scientists in 1987 in the first OLEDs were small organic molecules. Although small molecules emitted bright light, scientists had to deposit them onto the substrates in a vacuum (an expensive manufacturing process called vacuum deposition -- see previous section).

Since 1990, researchers have been using large polymer molecules to emit light. Polymers can be made less expensively and in large sheets, so they are more suitable for large-screen displays.

OLED Components

Like an LED, an OLED is a solid-state semiconductor device that is 100 to 500 nanometers thick or about 200 times smaller than a human hair. OLEDs can have either two layers or three layers of organic material; in the latter design, the third layer helps transport electrons from the cathode to the emissive layer. In this article, we'll be focusing on the two-layer design.

An OLED consists of the following parts:

• Substrate (clear plastic, glass, foil) - The substrate supports the OLED.

• Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows through the device.

• Organic layers - These layers are made of organic molecules or polymers.
  • Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.
  • Emissive layer - This layer is made of organic plastic molecules (different ones from the conducting layer) that transport electrons from the cathode; this is where light is made. One polymer used in the emissive layer is polyfluorene.

• Cathode (may or may not be transparent depending on the type of OLED) - The cathode injects electrons when a current flows through the device.

Making OLEDs

Photo courtesy Philips Laboratory set up of a high-precision inkjet printer for making polymer OLED displays

The biggest part of manufacturing OLEDs is applying the organic layers to the substrate. This can be done in three ways:

• Vacuum deposition or vacuum thermal evaporation (VTE) - In a vacuum chamber, the organic molecules are gently heated (evaporated) and allowed to condense as thin films onto cooled substrates. This process is expensive and inefficient.

• Organic vapor phase deposition (OVPD) - In a low-pressure, hot-walled reactor chamber, a carrier gas transports evaporated organic molecules onto cooled substrates, where they condense into thin films. Using a carrier gas increases the efficiency and reduces the cost of making OLEDs.

• Inkjet printing - With inkjet technology, OLEDs are sprayed onto substrates just like inks are sprayed onto paper during printing. Inkjet technology greatly reduces the cost of OLED manufacturing and allows OLEDs to be printed onto very large films for large displays like 80-inch TV screens or electronic billboards.

OLED's

Imagine having a high-definition TV that is 80 inches wide and less than a quarter-inch thick, consumes less power than most TVs on the market today and can be rolled up when you're not using it. What if you could have a "heads up" display in your car? How about a display monitor built into your clothing? These devices may be possible in the near future with the help of a technology called organic light-emitting diodes (OLEDs).

Photo courtesy Samsung Electronics Samsung's prototype 40-inch OLED TV

OLEDs are solid-state devices composed of thin films of organic molecules that create light with the application of electricity. OLEDs can provide brighter, crisper displays on electronic devices and use less power than conventional light-emitting diodes (LEDs) or liquid crystal displays (LCDs) used today.

Your cellphone as a credit card

Can I use my cell phone as a credit card?

by Julia Layton

January 12, 2007
Radio technology will soon do another consolidating act and remove an apparently extraneous "device" from your pocket: Your wallet. Or at least your credit card. If you're the type who never leaves home without your cell phone, you'll automatically have a credit card or debit card with you wherever you go thanks to an improvement on standard RFID technology called near-field communication, or NFC.

The NFC mobile-payment application is currently in trials in the United States, Germany, Finland, the Netherlands and a few other countries, with transportation ticketing as a primary use (think SpeedPass on a cell phone). The idea is that you just touch your phone to an NFC reader (or bring it to within a few centimeters), and it acts just like the credit card or debit card you use right now. A mobile-payment-enabled phone is associated with a bank or credit-card company just like it's associated with a phone-service provider. The technology is similar to the RFID (radio frequency identification) transmitters used in contactless credit cards (see How Blink Technology Works), except that NFC chips allow for two-way communication instead of only one way, which is supposed to make for a more secure payment method.

The technology behind NFC, like RFID, uses inductive coupling to transfer data. Induction occurs when a wire (or any other conductor of electricity) passes through a magnetic field, generating an electric current in the wire. It's similar to the principal of electromagnetism -- that passing an electric current through a coil of wire will generate a magnetic field -- only in reverse. An NFC chip has a coil of wire built into it, much like an RFID chip. When an NFC-equipped cell phone gets to within a few centimeters of an NFC-equipped payment station, which is generating a magnetic field and also has a coil of wire inside, an electric current jumps between the two coils of wire, signaling data-carrying, short-range radio waves to pass between the two devices.

Copyright © Nokia Corporation 2002. All rights reserved. Nokia 6131 NFC

Unlike the RFID tags in contactless credit cards, which only send information when asked for it, an NFC chip can also receive information. So when an NFC phone gets close to an NFC payment station, it can have a two-way conversation with the payment station. Instead of simply sending your name and credit card number when the data is requested via the circuit, the chip can have a conversation with the chip in the requesting device. It can say, for instance, "Not yet -- wait until my owner enters a password on my keypad." The pay station will then say, for instance, "Okay, I'll wait," and the devices will keep the connection open until the phone approves the transaction and sends the data.

Nokia revealed the first fully integrated NFC phone, the Nokia 6131 NFC, at the 2007 Consumer Electronics Show (CES) in Las Vegas. At CES, Nokia was in a perfect position to show off what some in the industry consider to be the myriad other applications for an NFC phone -- like sucking data off an NFC-equipped business card and downloading data from an NFC-equipped kiosk. The NFC chip is embedded underneath the cover of the phone. According to the NFC forum, you could also use an NFC phone to unlock the door to your house and synch your phone calendar with your PC calendar.

The 6131 NFC is in trials in New York City as of January 2007. Nokia says it should available to consumers by March. No word yet on which stores or transportation venues will be equipped with the standardized NFC readers.

For more information on mobile phones as payment methods and other NFC applications, check out the following links:

• NFC Forum
• PC Magazine: Nokia Intros NFC Phone That Doubles As Credit Card - Jan. 7, 2007
• CNET News.com: Sony, NXP to develop short-range wireless chip - Nov. 20, 2006

Noise-canceling Headphones

Photo courtesy Consumer Products Bose was the first company to introduce noise-canceling headphones.

Unfortunately for music lovers, many types of ambient sounds can interfere with or even block the sounds coming through their headphones. If you have ever tried to listen to a CD or MP3 player on a plane, then you know the problem well: The roar of the engines makes it difficult to hear what's being piped through the speakers -- even when those speakers are situated in or on your ear. Fortunately, noise-canceling headphones can provide a more enjoyable listening experience.

Noise-canceling headphones come in either active or passive types. Technically speaking, any type of headphone can provide some passive noise reduction. That's because the materials of the headphones themselves block out some sound waves, especially those at higher frequencies. The best passive noise-canceling headphones, however, are circum-aural types that are specially constructed to maximize noise-filtering properties. That means they are packed with layers of high-density foam or other sound-absorbing material, which makes them heavier than normal headphones. The tradeoff of all that extra weight is a reduction in noise of about 15 to 20 decibels (dB). But considering jet engines create 75 to 80 dB of noise inside the aircraft cabin, passive models have some serious limitations. That's where active noise-canceling headphones come in.

Decibel Defined A decibel (dB) is a measure of sound intensity. The dB scale is logarithmic, meaning that a change of 10 dB represents a tenfold change in loudness. So, a sound measuring 30 dB is 10 times louder than a sound measuring 20 dB.

Active noise-canceling headphones can do everything that passive ones can do -- their very structure creates a barrier that blocks high-frequency sound waves. They also add an extra level of noise reduction by actively erasing lower-frequency sound waves. How do noise-canceling headphones accomplish this? They actually create their own sound waves that mimic the incoming noise in every respect except one: the headphone's sound waves are 180 degrees out of phase with the intruding waves.

If you look at the illustration below, you can see how this works. Notice that the two waves -- the one coming from the noise-canceling headphone and the one associated with the ambient noise -- have the same amplitude and frequency, but their crests and troughs (compressions and rarefactions) are arranged so that the crests (compressions) of one wave line up with the troughs (rarefactions) of the other wave and vice versa. In essence, the two waves cancel each other out, a phenomenon known as destructive interference. The result: the listener can focus on the sounds he wants to hear.

Of course, several components are required to achieve this effect:

• Microphone - A microphone placed inside the ear cup "listens" to external sounds that cannot be blocked passively.
• Noise-canceling circuitry - Electronics, also placed in the ear cup, sense the input from the microphone and generate a "fingerprint" of the noise, noting the frequency and amplitude of the incoming wave. Then they create a new wave that is 180 degrees out of phase with the waves associated with the noise.
• Speaker - The "anti-sound" created by the noise-canceling circuitry is fed into the headphones' speakers along with the normal audio; the anti-sound erases the noise by destructive interference, but does not affect the desired sound waves in the normal audio.
• Battery - The term "active" refers to the fact that energy must be added to the system to produce the noise-canceling effect. The source of that energy is a rechargeable battery.

Using these components, noise-canceling headphones are able to provide an additional reduction in noise of 20 decibels. That means about 70 percent of ambient noise is effectively blocked, making noise-canceling headphones ideal for airline and train travel, open office environments or any other location with a high level of background noise.

While noise-canceling headphones do a good job distinguishing between the audio a wearer wants to hear and the background noise he or she wants to keep out, some people say that they compromise sound quality by muffling sounds. Users can also experience a change in air pressure, although ports built into the ear cup are meant to vent air trapped behind the speakers.

In spite of these tradeoffs, many people would never go back to normal audio headphones. That's because noise-canceling headphones do more than reduce noise. They also help alleviate fatigue when traveling, which can result from exposure to low-frequency noise for an extended period of time. You can even use noise-canceling headphones if you don't want to listen to another audio source but do want to cancel out background noise. And a little bit of quiet can be music to anyone's ears.

Electrostatic and Dynamic Transducers

Music versus Noise As the introduction to this article suggests, differentiating music and noise can be a subjective matter. But scientists make a clear distinction. Music is sound with a reproducible, distinct waveform. Noise refers to random and unpredictable waveforms. And white noise is the most complex type of noise because it contains many different frequencies, all possessing equal intensity.

To hear what's recorded on a record, cassette, CD, DVD or MP3 player, data stored on the medium must be converted into sound waves. This requires that the stored information be turned into an electrical signal, which then must pass through a transducer to convert the transverse electrical wave into a longitudinal sound wave that the ear can interpret. Speakers play the role of transducers in audio systems. They can be located far away from the listener's ear, however.

Headphones were developed specifically to solve this problem. Headphones are essentially speakers held over the ear by a band or wire worn on the head. They are categorized by the type of transducer technology use and by their construction. Let's look first at electrostatic headphones.

Electrostatic Headphones
Electrostatic headphones take advantage of a phenomenon that most people know as static electricity. When an object becomes charged, it either gains or loses electrons. An object that gains electrons is negatively charged; an object that loses electrons is positively charged. Objects with like charge experience repulsive forces, while oppositely-charged object experience attraction. These forces are known as electrostatic forces.

To create these forces in electrostatic headphones, a thin diaphragm -- a flexible sheet made of paper, plastic or metal -- is suspended between two metal grids or electrodes. When an audio signal is applied, varying attractions are created along the grids. This pushes part of the diaphragm toward one grid and pulls part toward the opposing grid. The resulting vibrations in the diaphragm produce the sound waves that are eventually detected by the ear.

Dynamic Headphones
Electrodynamic (or dynamic, for short) headphones are made of three functional parts -- a voice coil, a permanent magnet and a cone-like diaphragm. The narrow end of the cone is attached to the voice coil and actually generates the sound waves. It does this by vibrating rapidly in response to the vibrating voice coil, much the same way the three bones of the ear vibrate in response to the movement of the eardrum.

The vibration of the voice coil is made possible by two fundamental properties of magnetism:

• Identical magnetic poles repel each other, while opposite poles attract
• Electric current flowing through a coil of wire produces a magnetic field, with the direction of current flow determining the polarity of the magnetic field

When a voice coil is placed within the unchanging magnetic field of a permanent magnet, these two properties are realized. Switching the electrical signal that is pumped into the coil causes the North and South poles to switch back and forth very rapidly. As the North and South poles of the voice coil's magnetic field switch, they are attracted and then repelled as they interact with the permanent magnet. Because the permanent magnet is fixed and the voice coil isn't, the latter vibrates and transmits these vibrations to the diaphragm.

Noise canceling headphone

One man's noise is another man's music, but no matter what your taste, ambient noise is the enemy. Luckily, there's a piece of audio equipment designed especially to maximize your listening experience, keeping ambient noise out without sacrificing your music's sound quality. That piece of equipment is the headphone, and in this article, we're going to look at how headphones, especially noise-canceling headphones, work.

On a 1978 flight to Europe, Amar Bose, the founder of Bose Corporation, put on a pair of airline-supplied headphones, only to find that the roar of the jet engines prevented him from enjoying the audio.He started making calculations right there on the plane to see if it was possible to use the headphones themselves as a noise-reducing agent. Bose introduced the first noise-canceling headphones a decade later.

Shopping for noise-canceling headphones? Read headphones reviews and compare prices at Consumer Guide Products before you buy.

In order to understand headphones, you must first understand sound waves. You can check out How Speakers Work for some information, but we're also going to provide a brief introduction here.

When most people think of waves, they think of water waves, like you'd seen in an ocean or lake. A shallow water wave is an example of a transverse wave, which causes a disturbance in a medium perpendicular to the direction of the advancing wave. You can see this relationship in the illustration below. The illustration also shows how waves form crests and troughs. The distance between any two crests (or any two troughs) is the wavelength, while the height of a crest (or the depth of a trough) is the amplitude. Frequency refers to the number of crests or troughs that pass a fixed point per second.

Sound waves have many of the same characteristics as water waves, but they are longitudinal waves, created by a mechanical vibration in a medium that produces a series of compressions and rarefactions in a medium. When you pluck a guitar string, for instance, it begins to vibrate. The vibrating string first pushes against air molecules (the medium), then pulls away. This results in an area where all of the air molecules are pressed together and, right beside it, an area where air molecules are spread far apart. As these compressions and rarefactions move from one point to another, they form a longitudinal wave, with the disturbance in the medium moving parallel to the direction of the wave itself.

Longitudinal waves have the same basic characteristics as transverse waves. A compression corresponds to a crest, and a rarefaction corresponds to a trough. The distance between two compressions, then, is the wavelength, while the amount the medium compressed is the amplitude. Frequency refers to the number of compressions that pass a fixed point per second.

For sound waves, amplitude determines the intensity, or loudness, of the sound. Frequency determines the pitch, with higher frequencies producing higher pitch notes and lower frequencies producing lower pitch notes. The brain is able to interpret these characteristics of sound, but before that can happen, the sound waves must be detected by a sense organ. That, of course, is the ear's job. To learn more about how the ear detects and interprets sound, check out How Hearing Works.

The Home Theater set-up

Putting it All Together

Once you have all the components, it's time to set up the theater space. There are several factors to keep in mind when choosing and arranging the home theater room.

First of all, consider the architecture of the room. A home theater should be something like a movie theater -- you want an enclosed, rectangular room, with a good amount of space and not too much outside light. You need an enclosed space to get the best sound quality -- open rooms don't have ideal acoustics. If you are building a top-of-the-line theater, you may want curtained walls. This soft surface cuts down on disruptive echoes. For the same reason, it is generally better to have a carpeted floor than a wood or linoleum floor.

A custom-installed home theater system

Once you've decided what room to use, you need to figure out where to put everything. To find the best position for the television, just use common sense. It should be easily visible -- you don't want to crane your neck -- and it shouldn't be in a place that gets a lot of glare from outside. Put the television wherever it seems most logical, and build your system around that.

Getting the sound system in place is a bit more complicated. You should set the three front speakers up so that they are spaced evenly, all at about the same height. Also, make sure they are near the level of the television screen so that the sound seems to be coming from the action and actors you're watching on the TV. The idea is that you shouldn't be made aware of the speakers when you watch a movie -- your attention should be on the movie.

You have a couple of different options for arranging the rear speakers. Dolby Digital is designed for speakers positioned to either side of the listener, while Dolby Pro Logic systems should have the rear speakers behind the listener. In any case, the rear speakers should be mounted at the same height, spaced an equal distance from the listener. Of course, chances are you'll have more than one listener, so the spacing won't be equal for everybody. You can find the central listening position -- such as the middle of the couch -- and space everything according to that point, while still paying attention to other seats in the room.

It doesn't matter so much where you put your subwoofer. The low frequencies aren't directional like the higher frequencies emitted by the main speakers, so it can really go anywhere in the room. For the best rumbling effect, however, you should put the subwoofer on the floor or against a wall -- this will help the low frequencies carry through the room.

Once your television and speakers are in place, you'll need to calibrate them. Your television set may have a specific setup process for adjusting the color and brightness. Otherwise, you can use the THX optimizer found on many DVDs to perform your calibrations. You can also calibrate each speaker using a sound-pressure level meter. This will make sure that your speakers produce identical levels of volume.

Another thing to consider in your home theater is lighting. It's important that you don't have a lot of bright ambient light in the room, because this may cause glare on the screen or distract from the movie. But you also don't want a completely dark room, because the high contrast of the light from the screen may strain your eyes.

Ideally, a home theater should have soft ambient lighting connected to a dimmer. For the full theater experience, you can get an automatic dimmer and hook it up to the audio/video receiver. When you start up the movie, the lights will go down to a preset level on their own. Or you can control the lights with a remote control. Home theater systems can also be configured with curtains or cabinet doors operated by remote control. (Check out this site for more information on home-theater remote controls.)

As we've seen, the best home theater setup completely depends on your budget and your needs. If you just want a better entertainment system in the family room, a basic "home-theater-in-a-box" set, a DVD player and a good-sized television will be more than satisfactory. But if you want your own movie theater, with a huge screen and fantastic acoustics, you'll probably need to bring in a home theater expert and a contractor. The most important thing is to try everything out ahead of time to make sure your movies will look and sound great.

THX system

Home THX

If you want a top-notch home theater, look into a THX^®-certified system. If you've read How THX Works, then you know that THX is Lucasfilm's set of standards for movie-theater equipment and arrangement. Lucasfilm has also come up with certification standards for home theater setup, and if you want the best of the best, this is the way to go. The chief aim of Home THX standards is to ensure the highest-quality re-creation of actual theater sound.

Photo courtesy HowStuffWorks Shopper THX Ultra2 speaker system

There are currently two THX standards: THX Select, created with a 2,000-cubic-foot (57-cubic-meter) room in mind, and THX Ultra, for spaces with over 3,000 cubic feet (85 cubic meters). TXH Select2 and THX Ultra2 relate to receivers and amplifiers for the same two room sizes. THX has worked with electronics manufacturers to create equipment that lives up to the THX standards. THX has certified:

• Audio/video receivers
• DVD players
• Video screens - rated by their effect on acoustics
• Speakers
• Cables

A THX-certified home theater will cost you a good bit more than an ordinary home theater, because THX-certified components are mainly top-of-the-line equipment. If you just want a superior entertainment system in your home, you don't need to worry about THX systems. This sort of system is a luxury purchase, for connoisseurs driven to get the best possible sound out of their systems, or for folks with money to burn.

To find out more about THX home theater standards, check out the THX Web site.

Speakers

Speakers vary a great deal in performance, as well as price. The main rule in shopping for speakers, whether for a home theater or your stereo system, is to try the speakers out in the store and decide what sounds good to you.

For your home theater system, you will need several identical, standard speakers -- the exact number depends on how many channels you want for your surround-sound setup. You'll also need an optional subwoofer speaker for bass sounds. Ideally, you'll want to get at least five identical speakers to ensure rich sound from all sides, but this might not be feasible, depending on your theater space and budget. If you're looking to save money, you could even use your television's built-in speaker as the central front unit, but it won't give you the best results. Different speaker models handle sound differently, creating an unbalanced surround effect. To get theater-quality effects, you should get three identical, full-size front speakers.

Photo courtesy Sony Sony digital subwoofer

Photo courtesy Sony Sony micro speaker Photo courtesy Sony Sony in-wall speakers

The main full-size speaker options are floor-standing units, bookshelf units and in-wall units. Floor standing units are the largest, and they generally have the highest performance levels, as well as the highest price tags. Bookshelf units and in-wall units are more compact, which is great if space is limited, and they perform very well. They may lack some bass range, but a good subwoofer should adequately compensate for this.

Connection Upgrades When you're shopping for components, people may suggest that you upgrade the connectors that go between parts of your system. Shoddy wiring can certainly hinder a system's performance, but exercise caution if someone advises you to swap out all of the manufacturer's cables with high-end replacements. The difference you experience might not be worth the money.

Many home theater systems use more compact, generally less-expensive speakers for the two rear surround channels. This will usually give you fine results, and is often the best solution if you don't have space for full-size speakers in your theater room. Some people even prefer these smaller bipole and dipole speakers because they generate sound in multiple directions, giving a more diffused sound.

Another thing to think about is the speaker technology. You may want to consider electrostatic speakers or planar magnetic speakers instead of the conventional dynamic driver design. See How Speakers Work to learn more about these different technologies.

To make it easier to assemble a home theater system, many manufacturers have put together home theater speaker packages, putting front and rear speakers together in a set. These packages vary in price and quality, so you should give them a "test drive" before you buy, just as you would with individual speakers.

DVD vs. DVR

DVD Players, DVRs and Other Digital Playback

Most DVDs are formatted for one or more surround-sound formats and allow the picture to be presented in its original aspect ratio. For example, many DVDs present movies in widescreen format to match the way the movie looked in the theater, but they use a full-screen presentation for TV shows that originally aired that way. See How Video Formatting Works for more details.

Photo courtesy Audiophile Systems, Ltd. A high-end DVD player from Arcam

VCRs It's no secret that a VCR can't give you the quality that a DVD player can. But there are still good reasons to own a VCR. For example, you might still need a VCR to watch all the movies you bought before distribution went digital, or to view that second season of Twin Peaks that's not available on DVD. If you're planning a home theater, consider upgrading to a hi-fi stereo VCR for better playback.

Older DVD players have high-quality playback, but they can't record things you watch the way VCRs can. However, several DVD recorders are currently on the market. Of course, a DVD recorder is a little more expensive than a standard DVD player. But if you want to record a lot of shows, a DVD recorder might be worth the price.

Another recording and playback option is a digital video recorder (DVR). Unlike VCRs, DVRs store video in digital form, on a hard drive. Actually, when you hook up a digital video recorder -- such as a TiVo unit -- all programming is recorded on a hard drive, and then sent onto your television set a few seconds later. This means that you can pause a broadcast TV show, then resume watching it where you left off.

These units don't provide the programming -- you have to connect another video source, like a cable outlet or satellite dish. You also have to connect the unit to a phone line -- it makes a daily call to update its programming information. DVRs are a great option for people who want to record and watch a lot of shows. But the space on the hard drive isn't infinite -- on some models, you have to delete shows you have watched to make room for others you want to record.

Photo courtesy Newstream The ReplayTV 4000 DVR from SONICblue

In addition, several new digital video recording and playback technologies are emerging on the market. The two most prominent formats are Blu-ray and HD-DVD. Both use a blue-violet laser, as opposed to the red laser DVD players use. Blu-ray holds more data but is more expensive than HD-DVD. The jury's still out on which format will end up being the leader in the marketplace.

For more information on DVD players and DVD technology, check out our comprehensive article How DVDs and DVD Players Work. And, for more information on digital video recorders, check out How DVRs Work.

TV Reception

Television Reception

Just because it's called a "home theater" doesn't mean it's for watching movies only. You'll definitely want to watch television in your home theater, too. These days, you have a number of options to choose from.

In the United States, the most popular options are broadcast television (the signals you can pick up with a rabbit-ear antenna) and cable television. Analog broadcast and standard cable signals both transmit video with 330 lines of horizontal resolution. This is better than VHS video, but not as good as DVD or digital television. Analog cable and broadcast TV also feature programming with Dolby Pro Logic surround sound, but they cannot carry Dolby Digital. Another option is digital cable, which generally has a better picture than traditional cable.

The main advantage of both broadcast and cable is price -- broadcast is free, and cable is generally less expensive than satellite programming. Additionally, cable and broadcast television always carry local stations, while satellite service may not.

If you want to get the maximum use out of your home entertainment system while you're watching television, you should consider getting a direct satellite system, such as DIRECTV or DISH Network. To get satellite programming, you need to buy and install a satellite dish, hook the receiver up to your entertainment system, and then pay the monthly fees, just as with ordinary cable.

The main advantages of a satellite system are that you can get lots of channels and a better, digital picture (near the level of DVD). Some satellite programming still uses Dolby Pro Logic surround sound, but other providers support Dolby Digital surround sound on select channels. Some providers have separate packages for people who want HDTV. When shopping for a satellite system, be sure you get one that can do everything you want, and ask whether HDTV broadcasting will require a different or more expensive satellite dish. Also, be aware that the weather can affect a satellite TV signal. Depending on your provider, you may also be unable to watch different stations on different televisions at the same time.

DTV vs. HDTV

In addition to the television technology options, you also have to consider signal format when building your home theater.

For most of the history of television, there was only one kind of video signal -- analog. If you've read How Analog-Digital Recording Works, then you know that analog signals travel as a constant stream of information. In the case of video, the analog signal contains a stream of information telling a CRT television's electron gun how to paint lines on the phosphor screen. The problem with this sort of signal is that it degrades easily -- when you transmit video, you lose some of the picture quality of the original.

Over the past 10 years, digital television has taken its place alongside analog television. Digital video signals consist of bits of data, that is, sets of 1s and 0s. The advantage of sending information this way is that it can't degrade -- each bit has a set "either-or" value, so the signal will be exactly the same after transmission. Because they translate visual information so exactly, digital signals can carry much more detail than analog signals.

Widescreen Formats HDTV sets and some SDTV models have an impressive widescreen display. Traditional television has an aspect ratio of 4:3. This simply means that if the screen is four units wide, it's three units high. HDTV screens have a 16:9, or 1.78:1, aspect ratio -- the screen is 1.78 times as wide as it is high, more like a movie screen. For more information about the advantages of a wider screen, check out How Video Formatting Works.

The United States is changing its broadcasting from analog to digital television (DTV). Here's why:

• Because the signal can't degrade, digital televisions have superior picture quality.

• Digital signals are progressively scanned. If you've read How Television Works, then you know that a traditional television's electron gun paints only half of the picture lines in every pass. Digital video formats that feature progressive scanning paint the entire frame with one pass, which improves the fluidity of movement in a picture.

• Digital signals can provide much higher resolution than analog signals. Analog television supports standard-definition television (SDTV) resolution, which uses 480 horizontal scan lines of picture information. Digital broadcasts can handle this easily, and they can also allow higher resolutions, including high-definition television (HDTV), which boasts many more scan lines of picture information.

There's one important thing to remember here. General U.S. broadcasting is in the middle of a transition to DTV, not to HDTV. HDTV is the highest quality of DTV. During and after the transition to DTV, broadcasters will transmit signals in SDTV, HDTV and resolutions in between. Any new television set you buy will be able to read a DTV signal, but unless it's an HDTV set receiving an HDTV signal, you won't be getting all that extra resolution.

HDTV has a lot of advantages, but compatible sets also have a higher price tag. Right now, you can expect to pay $1,200 to $4,000 for an HDTV direct-view or rear-projection set, and $10,000 to $20,000 for an HDTV front-projection set.

Photo courtesy HowStuffWorks Shopper 82" rear-projection LCoS HDTV

If you'd like to have HDTV capability someday but you don't want to spend that kind of money now, you can get an HDTV-ready television. These sets have the necessary resolution capabilities to display an HDTV picture but don't have the necessary decoder to interpret the HDTV signal. Out of the box, they function just like traditional televisions, but you can buy a separate HDTV decoder that upgrades the set to display HDTV broadcasts. Some cable providers sell set-top boxes that will decode their HDTV signal. If your HDTV-ready television has a 4:3 aspect ratio, the picture will be cropped or letterboxed to fit the narrow screen size. For more information about HDTV and digital television, check out How HDTV Works.

There's one other important thing to keep in mind -- since the United States is in the middle of this transition, not all stations are broadcasting digitally. Some stations still broadcast analog signals, and these just don't look good on large-screen digital televisions.

Flat Screens

Flat-panel Screens

Flat-panel televisions don't have projectors or a scanning electron gun, so they're very thin and lightweight. If you plan to set up a home theater in a smaller room, this is a definite plus -- you don't have to worry about hauling a giant direct-view or rear-projection model in, and you don't need to figure out where to position a projector.

Photo courtesy Sony A flat-panel plasma television from Sony

The two primary types of flat-panel televisions are plasma and LCD. Plasma televisions create pictures with an array of cells that are a lot like fluorescent lamps. Flat-panel LCDs are similar to the screen of a laptop.

Plasma and LCD displays have great picture quality, but neither has a very good black level. They're cool and convenient, but they can also be expensive. LCDs are limited in size -- you can get much larger plasma displays or projection TVs. While plasma displays can be huge, they are susceptible to burn-in -- an image left on the screen for a long period can cause permanent damage. Recently, consumers have reported burn-in due to the logos some TV stations place in the corner of the screen.

The real benefit of a flat plasma screen is its compact size, and if you have a small theater space, this may be reason enough to shell out the extra money.

Projectors

Front-projection Television

Standard front-projection televisions work in pretty much the same way as rear-projection televisions, but the system is not contained in a television case. They are set up more like a film projector -- the projector is a separate unit, and you center the television image on a separate fabric screen.

Photo courtesy Newstream A high-end digital front projector from Sharp

The main advantage of a front-projection television is very large screen size. Since the components don't have to be packaged together, screen size is limited mainly by the room space -- what size screen you can fit in the theater, and how much distance you can put between the projector and the screen. Screens as wide as 200 inches are not uncommon. Projectors do vary in capacity -- make sure the projector is powerful enough to project a bright image across the room.

Most projectors work properly only in a darkened room. Consequently, they are really only suitable for a separate home theater space, rather than a family room or ordinary den. Since they are designed for watching movies, front projectors don't usually have a built-in television tuner: They don't receive television signals themselves, so they must be hooked up to a separate tuner (such as the tuner in a DVD player).

Front-projection systems use the same types of technology as rear-projection TVs -- CRT, DLP, LCD and LCoS. CRT systems can require professional installation, wiring and calibration. Other projector types can be easier to install, but they can also carry a pretty hefty price tag.

Rear-projection Television

If a very large screen size is important to you, look into rear-projection televisions. These sets don't have the same size constraints as direct-view televisions because they don't use the cathode ray tube for the display. Instead, they use a projection screen. There are lots of different types of rear-projection televisions. They include:

• Cathode ray tube (CRT), which uses three CRTs, one each for red, green and blue. These can produce a great picture with good contrast but can also be heavy and bulky.
• Digital Light Processing (DLP), which uses one or three digital micromirror devices (DMDs) to create all of the pixels that make up the image. DLP sets also create a good picture, but gaps between the micromirrors can produce a screen door effect. Some users also notice a rainbow effect when moving their focus from one part of the screen to another in sets that use only one DMD.
• Liquid Crystal Display (LCD), which directs light through liquid crystals and magnifies it for projection. An LCD TV can be lightweight and slim, but it doesn't have a good black level -- the ability to produce a true black, which is important for good detail and contrast.
• Liquid Crystal on Silicon (LCoS), which is like a cross between DLP and LCD. LCoS doesn't have the screen door or rainbow effects that DLP can produce. It isn't as common as other display types, and some sets don't have a very good black level.

Photo courtesy Sony A 53-inch widescreen rear-projection television from Sony

Some rear-projection sets may have a smaller viewing angle than direct view sets. No matter where you sit in front of a direct-view television, the screen maintains the same picture quality. If you look at a rear-projection screen from an extreme angle, the picture may be much darker and you won't be able to see what's happening on the screen. Newer projection sets use high-quality screens that work well from most angles, but older sets may have a fairly narrow viewing area.

If you're looking to buy a rear-projection television, the main things to compare are size, resolution and screen quality. Even a top-notch picture can look muddy on a bad projection screen, so be sure to pay attention to screen material. Darker screens are better because they present an image with better light-and-dark contrast. You should also look for a screen made of glare-resistant material.

Television

Standard Direct-view Television

The biggest variable in home theater systems is the television. You can go with a large-screen, direct-view television and spend as little as $300, or you can spring for a front- or rear-projection television, which could cost several thousand dollars. The main factors that determine television price are size and picture resolution.

Direct-view televisions are the sets that most of us are familiar with. They have a cathode ray tube (CRT) and a scanning electron gun that paints the picture on a phosphor-coated screen. Good direct-view televisions deliver an excellent picture, but because of the tube technology, they are limited in size. The biggest direct-view television screen you can get these days measures 40 inches diagonally.

Photo courtesy Sony A 32-inch direct-view television from Sony: A direct-view television is certainly adequate for a simpler home theater system.

This is a pretty big picture, of course, and will work well in a basic home theater setup. You might even be content with a 27-inch model. The general rule for television size is that you want a screen that measures about one-third your distance from the screen (if you sit 9 feet from the screen, a 36-inch television screen would be perfect). These are the guidelines for standard televisions, because if your screen is bigger, or you sit closer, the scan lines that make up the picture will seem fairly large, which translates to a lower resolution. This is inherent in the standard television signal -- it has a set number of vertical lines of resolution -- the number of horizontal lines in one screen -- no matter how big your screen is. High-definition television (HDTV) has more vertical lines of resolution, so you'll be able to sit closer and still see a clear picture when watching HDTV-formatted video.

Photo courtesy Sony With a 40-inch screen, the Sony Wega is at the upper limit of direct-view televisions.

When you're shopping for direct-view televisions, pay attention to image contrast. A television with a darker screen will give you a better picture because there will be a stronger contrast between light and dark -- black will actually appear black, rather than gray. You should also look for a television with a flatter screen. If the tube is more curved, the picture will be more distorted and you'll see more glare from other light sources. A perfectly flat screen will usually give you the best picture.

Surround-sound Formats

Which Surround-sound Format?

In the last section, we saw that audio/video receivers decode the surround sound information encoded in video signals and drive the appropriate speakers. Different audio/video receivers are equipped to decode different formats. Today, there are two main sources for home theater surround-sound formats -- Dolby Laboratories and Digital Theater Systems. Dolby Laboratories formats include various versions of Dolby Digital^® and Dolby Pro Logic^®. Digital Theater Systems has created a range of DTS Digital Theater Sound formats.

D-I-Y Surround Sound If you're really on a budget, you can rig your own surround-sound setup with four speakers and a regular stereo signal. See Accessing the Surround Channel for more information.

Between the two companies, there is a dizzying array of sound options. So here's what you need to know:

• DTS encoding uses less compression than Dolby encoding. This means that DTS sound is clearer and sharper.
• However, DTS encoding is also less commonly used on DVDs and television broadcasts.
• Most DVDs have some Dolby sound options, and some also offer choices for DTS sound.

Fortunately, a lot of a/v receivers support a wide range of Dolby and DTS options. When you're choosing a receiver, you should decide two things: whether you want DTS support and how many speakers you want to use for your surround-sound setup. The most common options are 5.1, 6.1 and 7.1 surround, named for the number of channels. The ".1" indicates a channel for a subwoofer. The subwoofer channel carries low-frequency sound to give a bass boost and create a rumbling effect for certain special effects sounds, such as explosions and trains. These are the typical speaker setups and formats that will support them:

• 5.1 (5 speakers + subwoofer)
  A 5.1 surround-sound setup includes left, center and right front speakers. It also has left and right surround speakers. Dolby Digital, Dolby Pro Logic II and DTS 5.1 will all support this format. DTS 96/24 uses a 5.1 channel format to play audio at the same sampling rate at which it was recorded.

• 6.1 (6-7 speakers + subwoofer)
  A 6.1 setup takes all the speakers from 5.1 and adds a rear channel. Dolby Digital EX uses this format, splitting the one additional channel into left and right rear speakers. DTS-ES, on the other hand, uses a rear center speaker. DTS Neo:6 can also support a 6-channel format.

• 7.1 (7 speakers + subwoofer)
  Dolby Pro Logic IIx has separate channels for the left and right rear speakers, rather than splitting one channel and directing it to two speakers.

The sound system is what really makes a home theater experience complete, but the first thing you'll probably notice when you sit down in front of a theater setup is the television. In the next few sections, we'll see how televisions fit into the home theater.

Audio Video Reciever

The Receiver

The audio/video (a/v) receiver and amplifier assembly in a home theater does the same job as the receiver and amplifier assembly in any stereo system: It receives signals from various input devices, like a VCR, DVD player or satellite dish. It interprets and amplifies those signals and then sends them to output devices -- your television and sound system.

Photo courtesy Sony A surround-sound stereo receiver from Sony

A home theater a/v receiver and amplifier assembly actually combines several different components. Some even have a DVD or other media player built in. You can generally assemble a superior home theater system by buying the components separately, but most people buy one unit that does all these jobs because it is more cost effective.

The receiver's components are:

• Audio/video inputs for video sources (DVD player, DVR)
• Preamplifier
• Surround-sound decoder (aka signal processor)
• Power amplifiers for each sound channel
• Outputs for speakers and television

The path of the audio and video is pretty straightforward. The source component (DVD player, DVR, etc.) feeds a signal to the receiver unit. You choose which input component you want to feed to your output unit, and the preamplifier selects this signal and amplifies its line level a little bit.

The receiver is at the heart of a typical home theater system.

The receiver sends the video on to your television and sends the audio to the decoder. The decoder sorts out the different sound channels from the video signal, and then sends the information to amplifiers for each sound-channel output. These amplifiers are connected to the appropriate speaker or speakers.

Digital decoders and analog decoders handle the job differently. Digital surround sound is quite simple: When a company is producing a Dolby Digital^® program, for example, they encode six separate audio channels, specifically balanced for a Dolby Digital speaker setup. A Dolby Digital surround-sound decoder recognizes these different channels and sends them to the appropriate speakers.

Analog surround sound is something else altogether. The different analog surround-sound channels are actually extracted from the two standard audio channels that make up any ordinary stereo signal. This is commonly called 4-2-4 processing because the encoder essentially takes the rear and front channels and works them into the ordinary stereo channels, and a surround-sound decoder separates the four channels out again. See How Surround Sound Works for more information.

There are a wide range of audio/video receivers available. These receivers are often sold with all the speakers you need, as a complete home theater system. These systems run as low as $250 and as high as $2,500.

Surround Sound

Surround Sound Basics

The main thing that sets a home theater apart from an ordinary television setup is the surround sound. For a proper surround-sound system, you need two to three speakers in front of you and two to three speakers to your sides or behind you. The audio signal is split into multiple channels so that different sound information comes out of the various speakers.

The most prominent sounds come out of the front speakers. When someone or something is making noise on the left side of the screen, you hear it more from a speaker to the left of the screen. When something is happening on the right, you hear it more from a speaker to the right of the screen.

The third speaker sits in the center, just under or above the screen. This center speaker is very important because it anchors the sound coming from the left and right speakers -- it plays all the dialogue and front sound effects so that they seem to be coming from the center of your television screen, rather than from the sides.

The speakers behind you fill in various sorts of background noise in the movie -- dogs barking, rushing water, the sound of a plane overhead. They also work with the speakers in front of you to give the sensation of movement -- a sound starts from the front and then moves behind you.

But how do all these sounds get split up? This is the job of the audio/video receiver, which is the real heart of a home theater. In the next section, we'll see what this component does.

Home Theater?

What Is Home Theater?

Home theater is difficult to define -- it's really just a vague term for a particular approach to home entertainment. Generally speaking, a home theater system is a combination of electronic components designed to recreate the experience of watching a movie in a theater. When you watch a movie on a home theater system, you are more immersed in the experience than when you watch one on an ordinary television.

To see how home theaters do this, let's take a look at the original model -- the movie theater. When it comes to picture and sound, the theater can offer an amazing experience we just don't get at home. That's usually why people will pay to go to the movies, even though renting a movie is cheaper. There are a few main components that make watching TV and going to the movies very different.

• One of the biggest differences is the sound experience. When you go to see a movie in a quality movie theater, you'll hear the music, sound effects and dialogue not just from the screen, but all around you. If you've read How Movie Sound Works, you know that a standard movie theater has three speakers behind the screen -- one to the right, one to the left and one in the center -- and several other speakers spread out in the rest of the theater.

  In this surround sound system, you hear different parts of the soundtrack coming from different places. When somebody on the left side of the screen says something, you hear it more from the left speaker. And in a movie like "Star Wars," you hear a rumbling swoosh travel from the front of the theater to the rear as a spaceship flies toward the camera and off the screen. You are more involved in the experience of watching a film because the world of the movie is all around you.

• The second chief component of the theater experience is the large size of the movie screen. In a theater, the screen takes up most of your field of view, which makes it very easy to lose yourself in the movie. After all, you're sitting in the dark with only one thing to look at, and everything you're looking at seems much bigger than life.

• We also enjoy going to the movies because we can see everything so well. Film projectors present very large, clear pictures. The detail is much sharper than what we see on an ordinary 19-inch television, and the movement is much more fluid. We may not consciously recognize this, but it does make a significant difference in how we enjoy a movie. When we can see more detail, we are more engrossed in the world of the movie.

The basic idea of a home theater is to recreate these elements with home equipment. In the next section, we'll look at an overview of what you need to get started.

LCD vs PLASMA

LCD vs Plasma Display Technology

Compare the two most popular flat panel display technologies.

Comparison	Plasma Display	LCD Display	Advantage
Screen Size	Screen sizes range from 32 inches to 60 inches	Sizes range from 13 inches to 40 inches, but larger screens are expected soon.	Plasma. Larger LCDs are already in development.
Viewing Angle	Up to 160°	Up to 170°	LCDs.
Screen Refresh Rates	Plasma displays refresh and handle rapid movements in video about as well as CRT televisions.	LCD TVs were originally designed for data display, and not video. Therefore refresh rates had to be improved. LCD TVs with refresh rates of 16 ms or higher show very little noticeable artifacts.	Slight edge to plasma technology.
Burn-in	Plasma displays can suffer from burn in produced by static images. After extended periods, stationary images "burn in" and produce an after-image ghost which remains permanently on the screen. Newer plasma models have addressed burn-in and reduced the issues of older models.	LCD panels do not suffer from burn-in.	LCDs
Product Life-span	Typical plasma displays have a life span of 20,000 to 30,000 hours, which equates to at least two years, three months of 24/7 usage before the image fades to half the original brightness.	LCDs life span is typically 50,000-60,000 hours, which equates to at least 5 years of 24/7 use.	LCDs run nearly twice as long as plasma.
Weight	Plasma displays are fairly heavy, and may need additional supports to be mounted onto a wall.	LCDs weigh less than comparably sized plasma screens.	LCDs are considerably lighter.
Durability	Plasmas are very fragile making them tricky to ship and install. Unlike the commercials where plasmas are mounted on the ceiling, plasmas are best installed by a professional, and should be installed on a wall that can bear a good deal of weight.	Much more durable then plasmas. End users can easily mount an LCD display themselves if desired.	LCDs are far less fragile than plasmas.
Shipping	Due to their fragile nature, plasma displays need to be shipped by specialty carriers. Overnight or fast delivery options are not recommended. Special shipping methods and their heavier weight add to higher shipping costs.	Shipping LCDs is not difficult, and is not as expensive as shipping plasma displays.	LCDs are lighter and far less fragile than plasma displays making shipping easier.
Installation	Plasmas are heavier, use more power, and run hotter than LCD displays, and therefore require more planning when mounting them. Plasmas are generally best installed by professionals.	End users can easily install LCD displays themselves, or can use them just as they use a traditional monitor/TV using a stand.	LCDs are much easier to install than plasma displays.
Brightness	Plasma displays range from 500-700 cd/m2, but are measured based on a different standard than LCDs. When compared under "real world" circumstances, plasma TVs brightness is typically closer to 100 cd/m2.	Measured under the more stringent "real world" standards, LCDs average a brightness rating of 450 cd/m2.	In the "real world" situations, LCDs are 4 times brighter than plasma displays.*
Thickness	As thin as 3 inches deep.	As thin as 2 inches deep.	LCDs are just a bit thinner.
Performance at High Altitude	High altitudes can affect the performance of plasma displays because the gas held inside each pixel is stressed, and has to work harder to perform.	LCDs are not affected by high altitudes.	LCDs.
Contrast Ratios	Current plasmas measure contrast ratios of up to 3000:1. However, when compared to LCD TVs in "real world" situations, contrast ratios for plasma displays drop to approximately 200:1.*	LCD contrast ratios are measured using "real world" standards. Typical contrast ratios range from 350-450:1. Some are as high as 800:1.	LCD contrast ratios measured in real world situations double typical plasma display's.