Just when you thought it was safe to sell your old CRT (Cathode Ray Tube) display and buy a flat screen, another competing technology comes along. It’s hard enough choosing between LCD or plasma screens, let alone the new arrival, OLED (Organic Light Emitting Diode) -- see Focus, PC Authority, issue 100. And while OLED has grabbed our attention, another technology has been gaining momentum, and may dominate in a few short years.
It’s called SED, otherwise known by its catchy full name: Surface-conduction Electron-emitter Display. Interestingly, it has more in common with your old-school CRT than with the latest generation of flat panel displays. This means that if its developers Toshiba and Canon can pull it off, SED could theoretically fuse all the strengths of CRT technology with those of LCD (Liquid Crystal Display) and plasma, without any of the weaknesses. Sounds too good to be true, right?State of play
Before we dive into the guts of SED technology, it’s worth pausing for a moment and asking the question: do we need another flat screen technology? Aren’t LCD and plasma -- along with OLED for smaller screens -- good enough?
Each of these screen types has its strengths and weaknesses, and none have been able to compete with relatively primitive CRTs in some key areas.
CRTs have been available for nearly 90 years so they’ve had time to mature. Even with the recent advances in LCD and plasma, CRTs are still best for black level, contrast and response time.
However, CRTs have a lot of unattractive qualities, such as the space they take up. They’re also susceptible to a range of unpleasant visual artefacts, such as moiré (interference pattern that leaves a grid or curved lines across the screen), geometric distortion (such as representing a circle on screen as an oval or ellipse), screen regulation (where the screen jumps in size when displaying a bright image compared to a dark image) and many more. They’re also limited in the size they can reach, with the largest practical CRT TVs topping out at around 107cm (42in), compared to an astounding 262cm (103in) found in Panasonic’s latest leviathan of a plasma screen.
Plasma screens can be much larger and thinner than CRTs, and have a higher peak brightness level and a black level close to that of a CRT. However, plasma screens consume vast amounts of power, and still struggle with fine colour gradation and detail at low brightness levels.
LCD delivers the highest definition, due to its small and tightly packed pixels, has decent brightness and is starting to become available in sizes above 107cm (42in), as was demonstrated by the monstrous 208cm (82in) Samsung LCD screen demoed at the 2006 CES event. On the other hand, LCD still suffers from below average contrast, relatively poor colour reproduction and pixel response time, plus they’re still extremely expensive, especially in larger screen sizes.
OLED, the poster child of screen technology, has much promise, but at this stage it looks more likely to evolve into a small screen product using the cheaper passive flavour of the technology rather than the larger ‘active’ form. This means it’ll be more commonly found in watches or mobile phones (rather than taking pride of place in the living room), at least for a few years yet.
OLED has potential when it comes to resolution, contrast and motion, but it has some large hurdles to leap before it becomes a viable big screen technology. Researchers are trying to overcome short screen lifetimes, the relative brightness of the different coloured pixels and reducing the cost of large active displays. The screens are also very susceptible to damage from moisture, which increases cost of manufacture due to the need to make them watertight.
What we need is a screen that combines the strengths of all the other technologies, without any of the weaknesses. Step forward SED.