By Alfred Poor, dealnews contributor There once was a time not too long ago, when consumers were so caught up in the massive difference between old-fashioned TVs (and even DLP types) and flat-screens, that they didn't even worry too much about how flat is flat. Now, though, the race is on for manufacturers to make the biggest and thinnest TVs they possibly can. How much thinner can a flat screen really get? The answers are different for the two major types of flat screens — plasma and LCD — so here is the scoop. Plasma Plasma HDTVs have the advantage of being less expensive than most LCDs of equivalent size and features. One of the trade-offs for this lower price is that the image generally is not as bright, so you need to be able to control the room lighting to get an equivalent picture. Plasma works much like a fluorescent light; you run an electrical current through a gas and it gives off invisible ultraviolet light. This hits chemical phosphors that glow red, green, or blue, depending on their chemical composition. These panels are relatively easy to build, and they can use low-quality glass for the front and back substrates. For years, the plasma manufacturers used the same thickness for their glass, mostly through inertia. In recent years, they have discovered that they can use thinner sheets, which saves on material and shipping costs. This can only provide limited reductions in thickness, however. Much of the space is taken up by the cells that are coated with phosphors. If you make the panel thinner, then the cells get smaller. This means that there is less room for the phosphor, which means that less light is produced. Increased efficiencies and smaller controlling electronics can help reduce the size of plasma panels, but at present they are still a few inches thick. Our most popular current plasma deal is the Panasonic VIERA 42" TC-P42S30 for $623 plus free shipping from 6th Avenue Electronics (with coupon code "AFL4COUPON"). Its width is 2.8", but that still can't match how thin LCD panels have become. LCD Unlike plasma panels, LCD panels do not produce any light on their own. The liquid crystal layer simply provides millions of tiny shutters that either transmit or block light. You need to put a very bright light behind the panel in order to produce an image that you can see. In fact, even when it is showing an all-white screen, as much as 95% of the light is absorbed by the panel, so the backlight has to be very bright. Traditionally, this light came from fluorescent light tubes that snaked across the back of the panel. These are relatively inexpensive to make, but they contain mercury with is an environmentally hazardous material. As a result, LCD display makers have turned to LEDs as a light source. They are highly efficient and very small, so they were initially adopted for use in mobile LCD devices such as cell phones and MP3 players. The cost of LEDs has dropped rapidly, however, and they have become much brighter. The first LED backlights for HDTVs simply replaced the fluorescent lamps behind the panel. This require lots of LEDs, but it made it possible to dim different regions of the screen to increase contrast and lower power consumption. Our most popular backlit LCD model listed at the moment is a 40" TCL Widescreen set for $400, that is less than 2" thick. Improvements in light guides and diffusers to spread the light out made it possible to move the LEDs to the sides of the LCD panel. This meant that the backlight became an "edgelight," and LCD HDTVs became much thinner. Initially, the LEDs were placed along all four sides of the panel, but brighter LEDs and better light guides have allowed manufacturers to use LEDs on fewer sides. One recent top pick by our readers was a Toshiba 3D bundle for $1,500, that is 1.15" thick. How far can this technology go? LG Electronics has demonstrated a 42-inch LCD HDTV that is just 2.6 mm thick. That is only as thick as a sheet of corrugated cardboard. This technology is not yet available commercially, but some products come very close to this. For example, the Samsung 9000 Series sets are less than a third of an inch thick, which is about three times as thick as the LG demonstration. How Thin Can You Get? Are we at the end of the line? Hardly! There are other technologies on the horizon that could result in even thinner television sets. LG has committed to starting a Gen 8 production line for OLED displays this year, which could be used to make panels as large as 55". OLED is an emissive technology — no backlight required — and it only needs one layer of glass as a substrate. As a result, the display panel could be as thin as a sheet of glass. And Corning can make high-quality glass that is as thin as 0.5 mm thick for Gen 8 panels (that's about 2 hundredths of an inch, or about half the thickness of a sheet of printer paper). You'll probably have to wait a few years before these new technologies are affordable, but the dream of a large screen HDTV that you can roll up like a window shade is not out of the question in the next five or 10 years. Alfred Poor, known on the web as the HDTV Professor, is an independent technology industry analyst and freelance writer based in Pennsylvania, specializing in PC-compatible microcomputer hardware and software products. He was a contributing editor to PC Magazine and Computer Shopper, and currently is a columnist at HDTV Magazine.