All TV technologies have some key problems with them:
- CRTs are heavy, use a lot of electricity, and have a practical size limit. The largest widescreen CRTs I know of are 34". The largest 4:3 aspect CRTs I know of are 40". This is a nice size, but is small compared to what other technologies can provide.
- Internal projection systems (CRT, DLP or LCD) can go to huge sizes, but there are brightness problems. Images tend to dim-out if you watch the screen from an odd angle. CRT-based projectors often suffer from burn-in, so they create problems for video games and those TV channels (like news channels) that have tickers and static images on-screen for extended periods of time. Replacement projector bulbs (for DLP and LCD units) can be expensive.
- External projection systems (LCD and DLP) can be projected to humongous sizes, but you need a place to put the screen, and the projector needs an unobstructed view of that screen. Lenticular screens (that give you maximal brightness) tend to dim-out when seen from odd angles. And replacement projector bulbs can be expensive.
- Plasma screens look great, but they can suffer from burn-in. They also tend to lose their brightness and/or focus after a few years. Considering how expensive these screens are, I can't see myself ever buying one. (But if you want to give me one for my birthday, I won't refuse to use it.
- LCD screens look great (and modern units don't have the off-angle fading and color distortions that were a problem in the past), but they can be very expensive. Especially at very large sizes.
SED can be thought of as the successor to CRT technology. A traditional CRT has a screen coated with phosphors that glow when hit by an electron beam. An electron gun at the back of the tube beams electrons at the phosphors to light them up. Deflector magnets bend the beam so it can hit more than just the phosphors directly in front of the beam. Circuitry manipulates the deflectors so the beam scans over the entire phosphor-surface 60 times per second (or faster, depending on the refresh rate), producing the image.
This is the reason CRTs can't get much larger than they are now. When the screen gets larger, you need more distance between the electron gun and the screen, since the deflectors can only bend an electron beam so far before it loses focus. Increasing the distance from the gun means you need more electricity (since the beam has a longer distance to travel), and it means the TV will get larger.
With SED, they eliminate this problem. Instead of a single electron gun, producing a beam, there are millions of micro-size electron-emitters. One for each pixel. Since each one beams its electrons straight ahead, there is no need for deflector magnets, and no need for a great distance between the emitters and the phosphors. The result is a screen with all the brightness, color definition, and off-angle quality of a CRT, but completely flat, and with lower power consumption. And there is no technical reason why SED panels can't be made as large as plasma screens - which means pretty much any size the public will be willing to buy.
I can also see these replacing LCDs as the display of choice for computers. Especially for graphic professionals. Large flat screens without all the contrast and color issues that professionals have with LCDs.
This tech is still experimental, so I don't know when we'll see commercial products, but hopefully it will be soon. This seems to me that it will end up being the best of all worlds (unless you want the wall-filling image size of an external projector, of course.)