A Surface-conduction Electron-emitter Display (SED) is a flat panel display technology that uses surface conduction electron emitters for every individual display pixel. The surface conduction electron emitter emits electrons, that excite a phosphor coating on the display panel which is similar to the basic concept found in traditional cathode ray tube (CRT) televisions. This means that SEDs can combine the slim form factor of LCDs with the high contrast ratios and can also refresh rates making the picture quality of CRTs better .The researches so far claim that the SED consumes less power than the LCD displays. The surface conduction electron emitter apparatus consists of a thin slit, across which electrons tunnel when excited by moderate voltages (tens of volts).

When the electrons cross electric poles across the thin slit, some are scattered at the receiving pole and are accelerated towards the display surface by a large voltage gradient (tens of kV) between the display panel and the surface conduction electron emitter apparatus. The SED display offer brightness, color performance and viewing angles on par with CRTs. However, they do not require a deflection system for the electron beam. Engineers as a result can create a display that is just a few inches thick which is still light enough for wall-hanging designs. The manufacturer can enlarge the panel merely by increasing the number of electron emitters relative to the necessary number of pixels. Since 1987, SED technology has been developing. Canon and Toshiba are the two major companies working on SEDs.

A surface-conduction electron-emitter display (SED) is a flat panel display technology that uses surface conduction electron emitters for every individual display pixel. The surface conduction emitter emits electrons that excite a phosphor coating on the display panel, the same basic concept found in traditional cathode ray tube (CRT) televisions. This means that SEDs use tiny cathode ray tubes behind every single pixel (instead of one tube for the whole display) and can combine the slim form factor of LCDs and plasma displays with the superior viewing angles, contrast, black levels, color definition and pixel response time of CRTs. Canon also claims that SEDs consume less power than LCD displays.

The surface conduction electron emitter apparatus consists of a thin slit across which electrons tunnel when excited by moderate voltages (tens of volts). When the electrons cross electric poles across the thin slit, some are scattered at the receiving pole and are accelerated toward the display surface by a large voltage gradient (tens of thousands of volts) between the display panel and the surface conduction electron emitter apparatus. Canon Inc. working with Toshiba uses inkjet printing technology to spray phosphors onto the glass. The technology has been in development since 1986.

A related technology also currently in development is Field Emission Display (FED) which uses multiple redundant emitters per area of display rather than a single emitter. SED is generally considered the more commercially viable of the two.

Canon began SED research in 1986 and, in 2004, Toshiba and Canon announced a joint development agreement originally targeting commercial production of SEDs by the end of 2005. The 2005 target was not met, and several new targets since then have also slipped by. This failure to meet mass-production deadlines goes as far back as 1999, when Canon first told investors of its intentions to immediately begin mass-producing the technology. The lack of tangible progress has worried many investors and has prompted many critics. One critic called SED “the best display technology you’ve ever seen that may be stillborn.” During the 2006 Consumer Electronics Show in Las Vegas, Nevada, Toshiba showed working prototypes of SEDs to attendees and indicated expected availability in mid-to-late 2006. Toshiba and Canon again delayed their plan to sell the television sets to the fourth quarter of 2007. At the 2007 Consumer Electronics Show, no SED displays were to be found on the show floor. This led many analysts to speculate that the technology would never reach the consumer market.

In October 2006, Toshiba's president announced the company plans to begin full production of 55-inch SED TVs in July 2007 at its recently built SED volume-production facility in Himeji.

In December 2006, Toshiba President and Chief Executive Atsutoshi Nishida said Toshiba is on track to mass-produce SED TV sets in cooperation with Canon by 2008. He said the company plans to start small-output production in the fall of 2007, but they do not expect SED displays to become a commodity and will not release the technology to the consumer market because of its expected high price, reserving it solely for professional broadcasting applications.

How it Works
SED technology works much like a traditional CRT except instead of one large electron gun firing at all the screen phosphors that light up to create the image you see, SED has thousands of tiny electron guns known as "emitters" for each phosphor sub-pixel. Remember, a sub-pixel is just one of the three colors (red, green, blue) that make up a pixel. So it takes three emitters to create one pixel on the screen and over 6 million SED emitters to produce a true high definition (HDTV) image! It's sort of like an electron Gatling gun with a barrel for every target positioned at point-blank range. An army of electron guns, if you will.

This may bode well for video purists who feel that CRTs offer the best picture quality, bar none. One prototype has even attained a contrast ratio of 100,000:1. Its brightness of 400cd/m2 is a tad on the low side for an LCD TV and nowhere close to a plasma. This is expected to increase in the future, but still works out to about 116 ftL (foot Lamberts) or more than twice a regular TV. To put this in perspective, a movie theater shows a film at about 15 ftL.

Life Expectancy
It does look like SED TVs will last a good while as it has been reported that the electron emitters have been shown to only drop 10% after 60,000 hours, simulated by an "accelerated" test. This means that it is likely the unit will keep working as long as the phosphors continue to emit light. That can be a while. Maybe yours will even show up on the Antiques Roadshow in working condition in the far distant future. Time will tell but "accelerated" testing results should always be taken with a grain of salt as it only imitates wear and tear over time.

SED TV Compared to CRT
SED is flat. A traditional CRT has one electron gun that scans side to side and from top to bottom by being deflected by an electromagnet or "yoke". This has meant that the gun has had to be set back far enough to target the complete screen area and, well, it starts to get ridiculously large and heavy around 36". CRTs are typically as wide as they are deep. They need to be built like this or else the screen would need to be curved too severely for viewing. Not so with SED, where you supposedly get all the advantages of a CRT display but need only a few inches of thickness to do it in. Screen size can be made as large as the manufacturer dares. Also, CRTs can have image challenges around the far edges of the picture tube, which is a non-issue for SED.

SED TV Compared to Plasma TV
Compared to plasma the future looks black indeed. As in someone wearing a black suit and you actually being able to tell it's a black suit with all those tricky, close to black, gray levels actually showing up. This has been a major source of distraction for this writer for most display technologies other than CRT. Watching the all-pervasive low-key (dark) lighting in movies, it can be hard to tell what you're actually looking at without the shadow detail being viewable. Think Blade Runner or Alien. SED's black detail should be better, as plasma cells must be left partially on in order to reduce latency. This means they are actually dark gray – not black. Plasma has been getting better in this regard but still has a way to go to match a CRT. Hopefully, SED will solve this and it's likely to. Also, SED is expected to use only half the power that a plasma does at a given screen size although this will vary depending on screen content.

SED TV Compared to LCD
LCDs have had a couple of challenges in creating great pictures but they are getting better. Firstly, latency has been a problem with television pictures with an actual 16ms speed needed in order to keep up with a 60Hz screen update. That needs to happen all the way through the grayscale, not just where the manufacturers decide to test. Also, due to LCD's highly directional light, it has a limited angle of view and tends to become too dim to view off axis, which can limit seating arrangements. This will not be an issue for SED's self illuminated phosphors. However, LCD does have the advantage of not being susceptible to burn-in which any device using phosphors will, including SED. SED is likely to use about two-thirds the power of a similarly sized LCD. Finally, LCD generally suffers from the same black level issues and solarization, otherwise known as false contouring, that plasma does. SED does not.