Plasma, LCD, projector, CRT? The choice of display technologies can be overwhelming for the un- or under-informed. Which TV should you next choose? SmartHouse helps you decide. CHOOSING LCD
Liquid Crystal Displays have been around for over 20 years, but have only recently become a reality in the TV market.
The reason for this is that their fundamental operation relies on crystals moving in a viscous liquid and, like wading in treacle, it’s a very slow process. Early generation LCD panels simply could not switch pixels on and off fast enough to cope with a moving video image, and consequently remained in clock displays and PC monitors that were predominantly used for near-static images.
Thankfully, as the technology has developed, the pixel-switching time has dropped dramatically and, in the very best models, causes very little motion blur on moving images. This has opened the floodgates for LCD TVs right up to over 50 inches. However, unlike plasmas, price is no indication of quality.
Hot or not?
LCD contrast ratio is generally poorer than any other TV technology as the backlight can leak through the “switched off” pixels. A potent backlight can lift the brightness figures, but colour is dependent on single block filtering, so the total range of colours and the colour saturation are also mediocre. The deep liquid crystal substrate means the picture integrity fades away as you move off axis, although the latest models claim a viewing angle up to 170 degrees. That said, manufacturer’s specification sheets can read like Tolkien-scale fiction at times, so getting a demonstration of an LCD TV before you buy is essential.
So why is LCD currently the must-have technology? Not only are LCD TVs a super slim flat panel, they are much lighter in weight than plasma models, as the LCD itself is made from plastic rather than glass. Screen resolutions are HD-friendly on larger screen models and each pixel has a much better defined edge definition than the glowing phosphor dots of plasma or CRT – creating a very sharp image. LCD TVs do not suffer screen burn-in from constantly displaying static images, are silent in operation and, from an energy-saving perspective, use little electricity.
But the biggest key to LCD TV’s rise has been falling prices. Each panel is cut out of a single large sheet of fully engineered LCD and each new manufacturing generation creates larger initial sheets. This reduces cost per unit and hence the street price.
LCD TV costs will continue to fall, the picture quality will continue to rise and, as features like digital tuners, memory card readers and wireless connectivity become mainstream, LCD TVs will dominate the 32 inch flat panel market.
As long as you make sure you are buying an HD-ready model and try before you buy, you can’t go wrong.
How LCD works
LCD technology works on the basis that light polarised in one direction will not pass through a filter polarised at right angles to it. An LCD panel consists of two sheets of polarising plastic filters and layers of electrically sensitive liquid crystals in between. When a voltage is applied to a pixel, the crystals turn through an angle. This effectively blocks light passing through the panel at that point, creating a “switched off” pixel. Add alternate rows of red, green and blue filters, put a strong light behind the panel and the result is a display capable of showing full-motion video. The slim construction results in an equally slim TV, suitable for wall-mounting.
While LCD gets all the attention, DLP TVs balance out stunning picture quality with a slightly fatter back-end.
Digital Light Processing has recently come of age. DLP rear projection TVs have hit the high definition resolutions of the best plasma models and do so at around half the price. In fact, the technology can offer brighter images than plasma with no screen burn-in, higher contrast than LCD and even better sharpness and picture motion than CRT. So what’s the catch?
As you’ll see from our description of how DLP works, it’s an indirect view display technology. Light has to be generated externally and reflected off the DLP chipset on to a screen inside a rear projection television. This means that the overall picture is not only dependent on the quality of the DLP chipset and image processing, but also requires excellent optics, pure light and a method of generating the primary colours – red, green and blue. Quality glass optics, UHP lamps and colour wheels spinning at exactly the correct speed do not come cheap and, as DLP is a patent technology of Texas Instruments, DLP TV builders have to buy TI’s devices.
All this technology has an impact on the price tag, and while DLP rear projection models are certainly cheaper than similarly specified plasmas, they are still a lot more costly than CRT TVs. On the up-side, the technology is easily scalable without a great impact to the manufacturing cost, so the larger the DLP screen, the better the relative value. Models start from around 40 inches but don’t really come into their own until 45-, 50- and 60-inch screen sizes, when they have a significant price advantage over larger screen plasma TVs. (One note of caution: the DLP projector bulbs are only likely to last you three or four years, but can be replaced.)
For the style and space conscious, DLP RP (rear projection) TVs are a half-way point between very deep CRT models and super-slim flat panels. Most are currently around 12 to 18 inches deep at a 50-inch screen size. They are generally fitted with decent sized loudspeakers too – making DLP models the best-sounding TVs available.
Almost every DLP RPTV model now sports HD resolutions of at least 1280 x 760 pixels and DVI or HDMI connectivity to hook up to HD sources as they become available. Simply don’t consider any models that do not have these features, and also look out for progressive scan and twin tuners to add quality and usability.
The viewing angle should be at least 140 degrees to ensure you can see the TV from every seat in your room, and physically check vertical viewing angles as older models can suffer reduced brightness if viewed from standing up.
As a final note of caution, make sure to ask what chipset it uses. Only consider models sporting HD2+ (DarkChip2), HD3 (DarkChip3) or HD4 technology. With the lower cost of bigger screen sizes, HD compatibility and ever-shrinking cabinet depths, DLP TVs have a very bright future.
How DLP Works
DLP technology uses a tiny chipset backed by a rectangular array of up to 1.3 million hinge-mounted mirrors, each measuring one-fifth the width of a human hair. This Digital Micromirror Device (DMD) is addressed by a video signal to individually tilt each mirror thousands of times per second, effectively turning pixels on, off or creating a greyscale. Light from a pure white lamp is reflected vertically off the chip, through a focusing lens and bounced from a large mirror on to the screen of the TV. This basic image is black and white, so a spinning wheel containing red, green and blue filters colours the image in fast refreshing frames.
The ultimate choice for the ultimate TV. But not all plasmas are created equal – if a model is cheap, it’s bound to be nasty.
If your prime reason for buying a new TV is simply to exude a classy air of style and sophistication then give up on other technologies and go for a plasma TV right away. Nothing has the big-screen hang-on-the-wall kudos of a large screen plasma.
But hang on just a minute. Did you know that most early generation low-cost plasma TVs have a resolution some 30 percent lower than the humble old tube TV and can’t even display the full resolution of standard definition broadcast TV? How about the fact that the brightness of a plasma TV begins to permanently decrease from the moment you switch it on, or that early models are susceptible to screen burn-in from static images such as channel logos? Possibly less well known is that the contrast ratio of some brand new plasma TVs can, in a brightly lit room, fall to a level that, were it a CRT TV, would be classed as irreparably faulty.
Avoiding The Rubbish
Basically the plasma market can be divided into two categories; the big brand name flagship models and the crap. Sadly the market is awash with unknown brand 42 inch plasmas with bargain price tags to make your credit card leap spontaneously out of your wallet. Grim resolution, contrast ratios and brightness figures are the norm here, and the most basic video processing is likely to show more artefacts and digital banding than a dot-matrix printer. Worse still, they will burn-in every still logo they display at length and will likely have a half-life (time to diminish to half brightness) less than 10 000 hours – that’s about three years of average viewing.
In the other camp, you have the pinnacle of TV technology; drop-dead gorgeous pictures in a sleek, stylish hang-on-the-wall package. The difference is, of course, the budget. The top crop of plasma TVs from Pioneer, LG and Fujitsu boast at least 1280 x 768 HD resolution and all the necessary DVI or HDMI connectivity to back it up. They have hi-tech video processing to emulate the smoothness of CRT and superb brightness and contrast ratios.
Each incorporates an array of software to reduce screen burn by subtle image-shifting, and the latest panels boast a 60 000 hour half-life.
Size-wise, plasma TVs tend to start off in the 42 inch segment, although 60 inch-plus screens are already available. As long as you choose a plasma TV with your head and eyes and aren’t seduced by a skanky bargain-basement cheapie, there’s really nothing to beat a big-screen plasma TV as an all-round paragon of home electronic technology.
How plasma works
A plasma panel is a great big sandwich of glass and the filling is an array of tiny sealed pockets. Hungry, anyone? There are three pockets per image pixel, each coated in either red, green or blue phosphors and filled with a plasma gas. Electrodes span these tiny cells and when electricity is applied the plasma gas gives off electrons that excite the phosphors into glowing. The sophisticated electronics in a plasma TV generate a range of electrical potentials between the electrodes of each cell, creating a range of colours and brightness levels for each pixel. The net result of the entire array being lit in this way is the video picture you see.
So what’s the catch? Well, quality projectors are going to set you back $4000 or more, plus you need a good screen to get the best results, and the image all but disappears if someone opens the curtains in daylight. Moreover, while the thought of having a screen to match the local multiplex might be appealing, the resolution of even DVD soon begins to show its limits if you go much larger than an 80-inch image size.
The technical issue of brightness really precludes a projector being your main source of TV viewing as it is impractical (and unhealthy!) to shut yourself in complete darkness to watch the soaps on a day-to-day basis. For dedicated movie watching on the other hand, they simply cannot be beaten for scale and impact. If budget allows, go for a direct view TV and a projector – adding a motorised screen to drop in front of the TV for some serious kudos.
Before you go rushing out to buy a flat-panel display just because it’s the latest technology and you can hang it on a wall, spare a thought for the humble old tube TV. Tube TVs are limited in their size and resolution abilities, but if you like your booty and don’t need a Hoyts-sized screen in your lounge then high-quality CRTs are still worth a look – if you can find them.
Cathode Ray Tube (CRT) technology is a golden oldie of consumer electronics. It’s been around since 1967 in colour form, and that’s a whole lot of time for manufacturers to get things right. In terms of picture quality per dollar there is nothing to beat a good CRT TV and manufacturers sticking with them still manage incremental increases in screen performance every year.
There’s life in the old dog yet
Despite this bargain basement status and venerable image, CRT holds a number of other benefits over newer TV technologies.
Its natural colour, superb contrast and super-smooth scrolling are second to none; it won’t lose brightness over time like plasma; and the viewing angle is much better than LCD. Okay, below a 14 inch screen size CRT becomes relatively too bulky and at over 32 inches, the additional weight of the glass tube means that you need to be a body builder to move it. But a CRT TV is also likely to outlast other technologies within the context of its limited existing connectivity, boasting a life expectancy of 12 years or more.
Many manufacturers – Sanyo and LG for, example – are now producing slimline CRTs that whilst nowhere near as skinny as their flat-panel brethren, are less obtrusive that the more traditional bloated versions.
How CRT works
Using a very high voltage, the electron gun at the neck of a TV tube causes a cathode (negative electrode) to emit rays of electrons towards an anode (positive). These streams are directed with a steering yoke through the vacuum in the TV tube towards the screen. They pass through a fine mesh called a shadow mask to further focus each beam on to red, green and blue coloured phosphors coating the inside of the screen. The phosphors are hit by the electrons’ glow, creating coloured points of light. Each line of phosphors is scanned 50 or 100 times per second (50Hz or 100Hz) to form what you see as the TV picture.
FUTURE TV TECH
A number of new display technologies are set to revolutionise the future of the humble TV.
Surface-conduction Electron-emitter Display is an evolution of good old CRT technology into a flat-panel form. Co-developed by Toshiba and Canon, SED collides electrons with a phosphor-coated screen to emit light. Tiny electron emitters, like miniature CRT tubes, are embedded between two glass layers each driving a single pixel. The advantage is that you get the super-high brightness and greyscale of CRT technology in a flat panel format, while neatly sidestepping the slow pixel refresh rate of LCD TVs or the ever diminishing brightness of plasma technology. SED TVs could appear as early as this year.