DIGITAL TELEVISIONS

LCD, LED, PLASMA, and DLP TVs

LCD Televisions

Liquid Crystal Display, or LCD TVs use a florescent backlight to send light through its liquid crystal molecules and a polarizing substrate. LCD TVs work passively, with red, green and blue pixels. By applying voltage to the pixels using a matrix of wires, the pixels can be darkened to prevent the backlight from showing through. Many LCD displays double as computer displays by allowing standard analogue VGA input, a great option if you need your display to pull double duty as a PC monitor to save money and space. Nearly all LCD TVs offer flexible mounting options including walls or under cabinets.

Bigger, faster, cheaper. LCD screens have broken the size barrier that once held them back (with models as large as 108”) and the larger screens have become affordable and economical to produce. LCDs now have contrast ratios equal to those found on more expensive Plasma and DLP models, and the “blur” effect, where the pixels cannot refresh fast enough for the screen motion, is extinct in newer models.

LED Televisions

LED TVs are technically a member of the LCD TV family. The display screen on a LED is a liquid crystal display the same as it is on any other LCD TV. The main difference between the two is different backlighting techniques.

The actual LCD panels are exactly the same as other LCD televisions.  Traditional LCD TVs use CCFL backlights (Cold Cathode Fluorescent Lamp) - thin fluorescent tubes with a diffusing panel inside to spread the light evenly around the screen.  Meanwhile, LED TVs use LED elements for the lighting source.

Traditional LCDs have used some form of flourescent lighting from tubes to much more advanced flat arrays of lights. LED TVs use Light Emitting Diodes to light the LCD panel. Just as there are different styles of flourescent lights in traditional LCDs there are also different styles of LED backlighting. There are LED TVs that have a panel of LED lights behind the LCD panel. In some the LEDs are tri-colored and can be controlled in banks for an effect called "local dimming". This allows darker areas of the picture to have the backlighting dimmed behind them resulting in better contrast and black levels. In the Luxia line of Samsung LED TVs, the LED lights are surrounding the edge of the panel and this arrangement allows for the very slim depth of those models. Without the ability to do local dimming these are functionally similar to traditional LCDs (but currently at a much higher cost).

Samsung does make LED-backlit LCD HDTVs (950 series) with local dimming technology, and they do offer excellent performance (though they cost significantly more than traditional LCD TVs). Sony and Toshiba also make LED-backlit LCD TVs (some models with with local dimming). Even VIZIO has announced a 55-inch LED-lit LCD TV with local dimming that they plan to start selling later in 2009. Currently these TVs are much more expensive than traditional LCD TVs, and even more expensive than high-end plasma TVs. But the costs should come down over time.

LED Advantages	LED Disadvantages
Local dimming LED TV technology has a clear advantage in contrast and black levels Thinner than LCD TVs LED TVs with colored backlighting have better color accuracy Viewing angles that rival Plasma TVs	LED TVs without colored backlighting are nearly equal to LCD TVs Response times and refresh rates are equal to LCD Tvs Power consumpition is higher - nearly equal to that of Plasma TVs LED TVs are much more expensive at the present time

---

Plasma Televisions

Plasma screens are basically a network of red, green and blue phosphors (each triad makes up a single pixel) mounted between two thin layers of glass. Plasma screens use a small electric pulse for each pixel to excite the rare natural gases argon, neon and xenon used to produce the color information and light. As electrons excite the phosphors, oxygen atoms dissipate and create plasma, emitting UV light. These rare gases actually have a life and fade over time.

Because all the pixels react at the same time, there is never any flicker apparent to the viewer. There’s also no backlight and no projection of any kind, so this results in a bright display with rich color and a wide viewing angle.

Most of the attention for plasma screens comes from their flat presentation and large screen sizes. They are able to be produced in sizes up to 80” (though not common) and yield a very nice picture. The downside is that they are power-hungry (not to be confused with the environmentally-friendly LCD screens) and really need to be professionally installed due to their fragile nature.

Unless plasma displays can miraculously adapt and compete in terms of longevity, brightness, (true) contrast ratio, power consumption and burn-in, the technology is on its way out. LCD displays are becoming cheaper, faster and more competitive.

Digital Light Processing (DLP) Television & Projection

DLP™ technology is based on an optical semiconductor called a Digital Micromirror Device, or DMD chip which was invented in 1987 by Texas Instruments. The DMD is basically an extremely precise light switch that enables light to be modulated digitally via millions of microscopic mirrors arranged in a rectangular array. Each mirror is spaced less than 1 micron apart.

These mirrors are literally capable of switching on and off thousands of times per second and are used to direct light towards, and away from, a dedicated pixel space. The duration of the on/off timing determines the level of gray seen in the pixel. Current DMD chips can produce up to 1024 shades of gray.

By integrating this grayscale capability with a 6 panel color wheel (2x RGB), the DLP system is able to produce more than 16 million colors. A DMD system can be made up of a single chip or 3 chips, resulting in even greater color reproduction. For example, DLP Cinema systems can reproduce over 35 trillion colors.

Advances are being made in the single DMD design. For example, Texas Instruments’ new HD2+ design incorporates an additional color (dark green) into the color wheel, allowing for contrast ratios greater than 3000:1 for much improved color reproduction and contrast. Apparently xHD3 technology is due out in late 2004 which will take the single chip technology to even greater heights by adding a new rear coating to the mirrors and eliminating more of the latent brightness when in the “off” position. Another upcoming technology is called Sequential Color Recapture (SCR) whereby DLP systems will replace the traditional color wheel with essentially, a “Spiral of Archimedes” RGB color pattern. This new technology has been mathematically projected to rival the current quality of 3-modulator DLP Cinema systems.

Adding more pixels to DMD-based systems may prove to be challenging as this requires larger and more costly microdisplays. Currently, shrinking the size of each mirror/pixel makes the DMDs impossible to mass-produce at reasonable cost. Right now, DLP is the front-runner in the technology war and, except for on the price-front, is pretty much the winner versus LCD and CRT technology.

The DLP 'rainbow effect' is an artifact unique to single-chip DLP projectors. The artifact appears as a rainbow or multi-color shimmer briefly noticeable when changing focus from one part of the projector screen to another. It appears as a secondary image that appears at the viewer's peripheral vision and is generally noticeable when shifting focus from a high contrast area or bright object.

3-chip DLP projectors, higher wheel speeds, 7-segment color wheels, and archimedes color wheel designs are minimizing or may altogether eliminate the effect.