Hardware Secrets

Uncomplicating the complicated

Everything You Need to Know About TV Technologies

by | Apr 10, 2008 | Consumer Electronics

[nextpage title=”Introduction”]

For decades, the remote control was the only major technological advance concerning television. Nowadays it seems every other week we get a glimpse of what the future of television will be like. From flat screen panels to new projection technology, there are so many options on the market that buying a new TV set could get complicated – and that’s where we come in; after all our motto is “uncomplicating the complicated.” Follow our tutorial as we open a trail into this jungle of acronyms.

Here is a list of what we will cover in this tutorial:

  • CRT
  • CRT Rear-Projection
  • DLP Rear-Projection
  • LCD Rear-Projection
  • LCoS Rear-Projection
  • Plasma
  • LCD
  • OLED
  • CRT Projector
  • LCD Projector
  • LCoS Projector
  • DLP Projector

[nextpage title=”CRT”]

This is our parent’s television – and probably the one you inherited and would like to replace by a shiny and new flat panel. CRT stands for “cathode ray tube” – a tube that houses an electron gun that shoots electrons in a beam that illuminates phosphors coating the inside of the tube, therefore forming a continuous image. There is an electron ray for each of the three primary colors: red, blue and green. The rays draw 525 horizontal lines over the screen (of which only 480 are actually visible). The whole thing works as rear-projection although the term is used for other TV technologies. CRT TV sets are big and heavy since the electron gun needs some distance to shoot at the glass-made screen. During the years the screens lost their roundness and became flat, decreasing loss of image detail over the edges. Screen size is limited to 42 inches and the energy consumption is equivalent to that of plasma sets, and considerably higher than LCD and rear-projection TVs. Thought obsolete when confronted with the arrival of plasma and LCD panels, the CRT is going through a rebirth as companies like Sony and Sanyo are releasing thinner CRT TV sets (about 20% and 30% thinner than older counterparts).

Model example: Samsung TX-T2782 (27,” SlimFit).

Strong points

  • Room brightness and viewing angle are not issues
  • Bright colors
  • Components have long life-span
  • Decreased price

Weak points

  • Great in size and heavy in weight
  • Mature technology
  • Screen size limited to 42 inches
  • High energy consumption

[nextpage title=”CRT Rear-Projection “]

This is the technology created to compensate for the bulkiness and screen size limitations of CRT TV sets. It has a gimmick well know to any magician worthy of his craft: a mirror. CRT rear-projection uses three ray tubes, one for red, one for green, and one for blue, to shoot electron beams unto a mirror at an angle, which reflects the image through a translucent screen. The better the tube’s lens, the higher the color fidelity and image brightness. Analog images can be formed by five to seven-inches tubes; high-def images (720 pixel-quality) need tubes with bigger lenses. The mirror gimmick allows the screens to go over 60 inches in size without the rear bulkiness it would create in a traditional CRT TV set – but it’s still a BIG final product. All rear-projection TVs look like pianos; they’re just like a big piece of furniture. Transport is a big issue: our 1998 57” Toshiba couldn’t enter the elevator and had to come by the stairs over seven floors, held by four men. A later model from Sony had to be discarded since its base couldn’t make a turn from the entrance corridor to the main room. Maintenance is very expensive: the 10 years-old Toshiba model underwent overhaul two times already and we paid a small fortune to get it fixed.

Model example: Panasonic PT-47XD64 (47”)

Strong point

  • The bigger screens for the lowest prices.

Weak points

  • It’s like a (big) piece of furniture and not a TV set.
  • Viewing requires a dark room.
  • Small viewing angle.
  • High maintenance.
  • CRT rear-projection is being dropped over LCD, DLP and LCoS rear-projection (reviewed later).

[nextpage title=”DLP rear-projection “]

Newer technologies like DLP, LCD and LCoS have brought rear-projection from the dark ages of the cathode ray tube. DLP stands for digital light processing. As with the older CRT rear-projection, a mirror is the key to its functioning.  Or, rather, mirrors: 1.3 million of microscopic mirrors, each corresponding to one pixel in an image. They are placed on the surface of a chip called DMD (digital micromirror device) and each one is about 1/5 the width of a human strand of hair. A lamp light source beams through a colored spinning wheel and hits the chip. The tiny mirrors tilt and rotate stimulated by several electrostatic discharges and reflect the colored beam of light unto the screen. The DMD chip can display high-definition images (720 or 1080 pixels) with 16.7 million colors.

Model example: Mitsubishi WD-65733 (65" 1080p HDTV)

Strong points

  • Excellent black level and contrast ratio
  • Greater viewing angles than those of CRT rear-projectors
  • No burn-in such happens with plasma
  • Less bulky set than those of CRT rear-projectors.

Weak points

  • Chip substitution can be expensive
  • “Rainbow effect”: some sensitive eyes notice the rapid changing of color spectrum (red, green, blue) caused by spinning wheel between the lamp source and the DMD chip.

[nextpage title=”LCD Rear-Projection “]

Please do not mistake flat-panel LCD (which we will talk about later) with rear-projection LCD. While in DLP rear-projectors the light is reflected by the mirror-coated DMD chip, here it goes through a liquid crystal chip made of several pixels to form an image. An electric current stimulates the pixels to either let the light go through or block it. The system uses three colored LCD chips (red, green and blue) to create the final color image. Resolution depends on the number of pixels contained in the chip – it goes as high as 768 but does not achieve Full HD status (i.e., 1080 pixels). Defective individual pixels are a problem: they can either go dead, appearing as a black dot on the screen, or be forever lit, and therefore being seen as a white dot. Other common problem is the “screen-door effect”: individual pixels can be seen forming the image on the screen.

Model example: Panasonic PT52LCX66 (52”)

Strong points

  • Even tough is way bigger than its flat-pannel cousins, the LCD rear-projection is still less bulky than a CRT rear-projectors.
  • Low energy consumption.
  • Cheaper maintenance than those of DLP rear-projectors.

Weak points

  • Bulkier set than those of DLP rear-projectors.
  • Poor black level: the closest it gets is a very dark gray.
  • Fixed number of pixels.
  • Defective pixels.
  • “Screen-door effect”: individual pixels can be seen forming the image on the screen.

[nextpage title=”LCoS Rear-Projection”]

It’s like a hybrid between LCD and DLP rear-projection technologies. LCoS stands for liquid crystal on silicon and follows the same reflexive concept from DLP; only instead of a tiny mirror-covered chip, it uses a coating of several individual liquid crystals. The light hits the silicon chip and is reflected by each stimulated liquid crystal forming the image. Color is generated through two methods: a spinning colored wheel akin to DLP technology, or a display chip per primary color, with the images being combined optically. Screen resolution reaches Full HD (1080 pixels). Sony’s SXRD (Silicon X-tal Reflective Display) and JVC’s D-ILA (Digital Direct Drive Image Light Amplifie
r) are proprietary variations of LCoS technology. Heralded as the future of rear-projection, LCoS is being dropped by several companies such as LG and Sony.

Model example: JVC HD70FH96 (70")

Strong points

  • Reaches higher resolution than those of LCD rear-projectors.
  • No “screen-door effect.”
  • No risk of defective pixels.
  • Chip substitution can be expensive.
  • High contrast and color fidelity.

Weak points

  • Expensive.
  • Dropped by major companies.

[nextpage title=”Plasma”]

It’s time to enter the realm of futuristic flat-panel TV, the kind of display that existed in science fiction for decades before becoming real with the advent of plasma and LCD televisions. Let’s talk about plasma first: the display is composed of two panels of glass holding tiny cells full of a mixture of noble gases (xeon and neon). An electrical charge turns the gas into plasma. The ultraviolet photons emitted by the plasma excite the phosphor coating in the back of each cell to give off colored light. They become like fluorescent lamps and can be ionized 85 times per second. The latest generation of plasma displays has a lifetime of 60,000 hours, or 27 years at 6 hours per day. After that, the brightness level goes down by 50%. Bear in mind that a traditional CRT television loses about 30% of its brightness after 20,000 hours of use.

The main problem concerning first generation plasma displays was screen burn-in. Static images like TV channel logos and other graphical elements could over time burn them unto the screen. The phosphor was to blame since it got tired of the pixels being lit and unlit over and over following the same pattern to form a particular image. Nowadays the plasma manufacturers have devised several countermeasures to screen burn-in, like improving the quality of the phosphor coating and washing routines to shake up the static graphical elements so they cannot be imprinted upon the screen. Plasma displays can reach resolution of Full HD and be as big as 150 inches (like a recent model unveiled by Panasonic). The technology, however, is loosing ground to LCD displays. A study that included consumer surveys spanning six countries in three regions – North America (United States and Canada), Asia Pacific and Europe (United Kingdom, France and Germany) – said that plasma TV will have less than 15% of the flat-screen displays market share by 2011.

Model example: LG 50PG20 (50” 720p HDTV)

Strong points

  • Can be as big as 150 inches.
  • Excellent black level and better colors than LCD.
  • Big viewing angle.

Weak points

  • Risk of burn-in still exists.
  • High power consumption.
  • Gets hot.
  • Models are 20% heavier than same screen size LCD counterparts.
  • High resolution models are more expensive than LCD with the same screen resolution.

[nextpage title=”LCD”]

After reviewing the rear-projection LCD, it’s time to see what the LCD flat-panel is all about. The technology contains sheets and cells of liquid crystal to be polarized by an active matrix of TFT (thin-film transistors). Two thin layers of glass substrate are held together by polarization. One of them has the interior coated by a polymer to hold several tiny cells filled with liquid crystal. A pixel is comprised of three cells – one red, one blue, and one green. When an electrical charge goes through the system, the crystals either block or let the light coming from the back, making the cells work like shutters of a photographic camera. The so-called “response time” of LCDs concerns the speed of this tiny liquid crystal shutter opening or closing. The higher the response time, the longer the cell blinks, and the longer it gets to portray a new image – so the last one appears as a ghost on the screen. A high response time incurs in this “ghosting effect.” There’s also the chance of the pixels getting defective just like in rear-projection LCD technology. The flat-panels don’t get as big as the plasma rivals – the biggest LCD TV is a 108 inches model from Sharp. According to NPD Group, LCDs accounted for 60% of total TV sales in 2007 in the United States.

Model example: Samsung LN46A550 (46” 1080p HDTV)

Strong points

  • No burn-in susceptibility as it happens with plasma.
  • Higher resolutions for a better price than the same high res plasma models.
  • Low power consumption.
  • Cooler running.
  • Work well in brightly lit rooms.

Weak points

  • Ghosting effect in high response time displays.
  • Defective pixels.
  • Poor black level.

[nextpage title=”OLED”]

This is sort of the next generation of LCD. So far only Sony has unveiled a TV using this technology, release in December in Japan. OLED stands for organic light-emitting diode. Unlike LCD, whose pixels require a backlight layer, OLED pixels provide their own light through electrophosphorescence – so the device is thinner and power efficient. The end image has sharper colors and a true black level (and not the dark gray that LCD features). Take our word for it: it will be the future of flat-panels.

Model example: Sony XEL-1 (11”)

Strong points

  • Thinner than plasma and LCD televisions.
  • True black level and sharper colors than LCD.
  • Big viewing angle.
  • Cheaper manufacturing cost than the LCD active matrix (TFT).

Weak point

  • Organic elements have a small lifetime (14,000 hours).

[nextpage title=”Projectors”]

A projector is not a television per se, but a device that takes a video signal and projects the image on surface (a screen or even a wall) using a lens system. The concept is the same as in a movie theater. Their common display resolutions include SVGA (800×600 pixels), XGA (1024×768 pixels), 720p (1280×720 pixels), and 1080p (1920×1080 pixels). The brighter the lamp inside the projector, the better the final image – and the brighter can be the viewing room. A lamp’s light output is measured in lumens.

All the rear-projector technologies we’ve just reviewed also apply to video projectors, following the same principals. We’ll do a quick recap of those technologies, now taking in consideration the characteristics of front projection.

[nextpage title=”CRT Projector”]

The cathode ray tube projector works just like in the good ol’ television sets. The projector consists of three tubes, each dedicated to one of the primary colors; a lamp; a circuit board to manage the video signal; and a set of lenses to focus and amplify the light beamed from the lamp through the tubes. Since the image is formed by electrons horizontally scanning lines and not pixels being lit or unlit, the resolution is not pixel-limited like in other rival technologies as LCD or DLP. CRT projectors can be found in college auditoriums and movie theaters, where they’re used to display commercials prior to the main feature.

Model example: CRT projectors are currently hard to find. Sony Superbright VPH-1031 was a popular model many years ago.

Strong points

  • Long lifetime (20,000 hours against 1,000 or 2,000 of rival technologies).
  • Greater black level than LCD and DLP based projectors.
  • High resolution limit (1920×1200 pixels).

Weak points

  • Very heavy and bulky.
  • Requires a very dark viewing room.
  • Prone to color divergence if not finely tuned.

[nextpage title=”LCD Projector”]

The projector functions by sending light from a metal halide lamp to three transparent red, blue and green silicon chips covered in liquid crystals. As the polarized light passes through the LCDs, individual pixels react by opening or cl
osing, influencing the light flow and forming images to be projected on a screen. The number of pixels available in the system limits the maximum resolution of the final image. As a metal halide lamp is smaller than the one used on CRT projectors, the whole set is more compact. LCD projectors are favored by multimedia presenters and do not get much home theater usage.

Model example: Mitsubishi HC4900

Strong points

  • Small, light and compact.
  • Cheaper than CRT projectors.

Weak points

  • Low service life (1,000 or 2,000 hours of lamp brightness).
  • Prone to screen-door effect.
  • Defective pixels.
  • Resolution is pixel-limited.

[nextpage title=”LCoS Projector”]

LCoS combines aspects from both LCD and DLP technologies. Just like in LCD projectors, LCoS also uses three colored chips at its heart, although the light doesn’t pass through them, but is reflected just like in DLP – not by micromirrors covering the chips, but by the liquid crystals on their surface. As they operate in high resolution (1365×1024 pixels SXGA), LCoS are very expensive – and also heavier than LCD and DLP counterparts. Because of that, they are more used in home theaters than in multimedia presentation.

Model example: Sony VPL-VW40

Strong points

  • No screen door effect.
  • No rainbow effect.

Weak points

  • Low service life (1,000 or 1,500 hours of lamp brightness).
  • Low contrast.
  • Not portable.
  • Expensive

[nextpage title=”DLP Projector”]

It functions just as the rear-projector version. The lamp shines light through a spinning colored wheel and then over the DMD micromirror-covered chip to be reflected to the lens, where the resulting image is focused and amplified to the screen. Since there are models with Full HD 1080p resolution, the DLP projector is favored by home theater enthusiasts. The same technology is also used in DLP-based movie theaters with special 3-chip projectors capable of displaying 35 trillion colors.

Model example: Optoma HD80

Strong points

  • Full HD resolution makes it compatible with Blu-Ray and HDTV.
  • Low power consumption.
  • High contrast and brightness.
  • No screen door effect.
  • Compact.

Weak points

  • Low service life (1,000 or 2,000 hours of lamp brightness)
  • Prone to rainbow effect.