HDTV - Television Re-defined

How old is High Definition TV?

On the 2nd November 1936 broadcasts began from a transmitter at Alexander Palace in London, of what was then described as the world's first "high definition" Television service. The phrase was used to distinguish the crisp (?) new 405 line TV images from the barely intelligible puddles of light and dark produced by earlier systems - such as Logie Baird's mechanical scanning system. Which just goes to prove that in defining TV picture quality, as with so much in life, it is all relative!

Nevertheless, 70 years later, we now have available a High Definition TV system that would surely astonish those early TV pioneers. The tough objective that has been driving HDTV development forward for the last thirty years - to match, on a home TV screen, the definition of projected 35mm cinema images - has now been realised. But it has only been achieved by drawing heavily on highly advanced technologies from a number of different areas, including complex digital encoding/ decoding strategies, super fast computer chippery and - supremely - the imaging technology of advanced colour TFT LCD.

The tube is dead. Long live LCD

Although startling results have been achieved with "traditional" cathode ray tube imaging in recent years - for example with the super high resolution Trinitron tubes originally developed by Sony for Air Traffic Control applications - it had become increasingly clear that the resolution - and affordability - demands of a device for bringing HDTV into the home - were just pushing tube technology too far. The limitations of the shadow mask structure, difficulties with scanning spot size (and shape) control, power demands of very fast scanning circuits, susceptibility to magnetic fields, added to the fundamental technical weakness of having to construct images out of lines rather than dots - all of these have meant that the imaging device that has reigned supreme since those early Alexandra Palace broadcasts must now make way for Liquid Crystal Display.

LCD technology itself of course has had to surmount huge technical barriers to enable the kind of HDTV quality now becoming available to all. Ironically the severe demands of image definition needed for HD - the cause of the CRT's demise - has been in many ways the least of the difficulties in LCD development.

For LCD, problems such as image sluggishness and lag, colour impurity and unevenness of illumination, problems of designing the circuits needed to address and refresh - at lightning speeds - the vast array of pixels forming the screen, added to the basic market demand for larger screen sizes to match those previously available with CRT, all these and more have concentrated the minds of development teams in the Far East and elsewhere.

Dust to (no) dust, ashes to...?

From the point of view of convenience and - above all safety- what does the massive switchover from tube to LCD mean for the home user. Every housewife (and house-husband) who flicks a duster round the living room once a week will have noticed that these new TV sets are not the great dust accumulators that their predecessors were, which of course is due to the elimination of the high internal voltages (typically 20 kV or more) and resultant static which has always be-devilled TV tubes.

But does this mean that this new lower voltage technology of flat-screen is inherently safer? Are the days now gone when forensic investigators of house fire tragedies so often pointed the finger of suspicion at the humble TV as the probable cause? Certainly the possibilities of fires arising from internal arcing and breakdown are considerably reduced - but both of the main standards for home electronic products (EN 60950 and EN 60065) take cognizance of the fact that any point in an electronic circuit where a crack or bad solder joint could dissipate 15 watts or more is a "Potential Ignition Source".

But flat screen sets bring other safety hazards. The dream of "a TV set you can hang on the wall" has at last come true, but how secure is the wall fixing? Plasma based flat screen sets in particular are heavy and can cause considerable damage and possible personal injury if they come adrift. And what about the stability of table mounted sets? Whilst the new EN 60065 standard has detailed and thorough tests for tilting and rocking they can not take into account the adventurous toddler who finds his hands can gain a purchase on the thin, top edge of a flat panel TV - possibly pulling it down on top of him.

Cool Technology?

LCD TVs tend to run cooler than their CRT predecessors it is true, but often the designers have achieved this - in part - by the all-too-common practice of moving the power conversion circuitry (mains to DC) outside the equipment itself: moving it into one of those familiar small black boxes of the sort that now clutter up the mains wall sockets all over the house - and particularly around computers. Quite apart from the serious environmental concern about these adaptors drawing power 24-7 there is the simple fact that they get hot - and they got even hotter if curtains are allowed to drape over them or they are enclosed in a confined space behind furniture.

For the direct plug-in type of adaptor the retention and good contact within the wall socket is another area of concern, especially as compliance with the British Standard for mains plugs and sockets (BS 1363) is not mandatory for such devices.

These are typical safety issues that arise with many electronic products around the home and that exercise the judgement of the various bodies charged with monitoring the safety aspects of equipment as the technology evolves.

So while TV image performance has now reached such an impressive level, improvements in the inherent product safety of TV receivers continues to be an evolutionary process that will require continued competent market vigilance and the ongoing expertise and experience of safety authorities (such as ASTA BEAB), for the foreseeable future.

About the author: Gareth Price is a Senior Safety Approvals Engineer at ASTA BEAB Certification Services. With over 30 years of experience in the electrotechnical industry, he specialises in the test and approval process for televisions and has worked in both manufacturing and test environments as well as for broadcasters LWT.