Friday, December 30, 2005
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Monday, December 12, 2005
For people in the market for a large screen TV, either for a home theatre system or a classroom/boardroom presentation setting, a Projection TV is the most efficient choice.
CRT or cathode ray tube set's size maxes out around 40", and at that size they are extremely heavy and bulky. Plasma displays are manageable with larger screen sizes but can be very expensive. Projection TV technology can create very large screen TVs which are not only manageable but affordable.
Projection televisions have four main components: a projector, screen, control panel, and a sound system. There are two main types of projectors used for these TVs: a transmissive projector, where light shines through the image forming element (CRT tube, LCD panel), and a reflective projector in which light is bounced off of the image forming element. In both projectors, a lens gets the image from the image forming element, magnifies the image and focuses it onto a screen. Top of the line projection TVs use primarily reflective projectors because the advances in reflective projector technology of late have been more progressive than those pertaining to transmissive projector technology.
The image forming elements used in transmissive projectors are CRTs and LCDs. TVs using a CRT for projection actually have a small (around 9" diagonal) television built in. A lens in front of this small, extremely bright CRT TV magnifies the image and projects it onto the screen. Three basic configurations are used in these sets. Transmissive projectors using an LCD for projection are substantially lighter with a higher resolution capacity than their CRT counterparts. The LCD panel used in projection TVs is very similar to that of a full sized LCD only smaller and brighter. This panel is backlit by a halogen lamp, the image on the panel is transmitted through a magnifying lens and projected onto a screen.
Reflective projectors use a small reflective chip to form the image. When light shines on this chip, it is reflected off of it, through a projection lens and onto the screen. The most exciting developments in projection TV technology have been made with reflective projectors using micro-electromechanical systems and liquid crystal on silicon.
With advances in LCD and MEM technologies, projectors will become smaller and form closer competition between projection TVs and the new plasma displays, in areas such as resolution and crispness of image detail. A relatively new application of projection TV technology is, "virtual reality", in which the viewer feels surrounded by, or as though he/she is a part of, the image being viewed. Projection TVs may not be the next big thing to hit the shelves, but we can be sure they will continue to be a viable, low priced option when shopping for your new TV.
Tuesday, December 06, 2005
The LCD face consists of two transparent layers which polarize a liquid crystal layer sandwiched in between. The front layer of glass is etched with a grid pattern on the inside surface to form a template for the liquid crystals. Liquid crystals are rod shaped molecules that bend light in response to an electric current; the crystals align so that no light can pass through. Each crystal acts like a camera's shutter, either blocking light or allowing it to pass through. A pattern of transparent or dark crystals forms the image. This same technology has been around for a while, even in such unsophisticated items as digital watches.
LCD TVs use an "active matrix" LCD; the most advanced type of LCD. The active matrix design is based on TFT, or thin film transistors. These are tiny switching transistors and capacitors that are arranged in a matrix on a glass substrate, they switch the LCD pixels on and off. In a color TV's LCD, each color pixel is created by three sub-pixels with red, green, and blue color filters.
One of the biggest challenges for LCD TV manufacturers has been speeding up the pixel response time, (how fast an individual pixel's color can change without blurring) so that fast moving images don't exhibit motion lag or "ghosting". This is especially critical for larger-screen LCD TVs, or for LCD TVs on which much of the viewing will be HDTV, or DVD movies.
An important difference between LCD technology and Plasma is that an LCD screen doesn't have a coating of phosphor dots; LCD TVs color is created through the use of filters. This keeps image burn-in from being a problem--- which is good news in particular for people who might use a video gaming system or PC on their TV. Another benefit of owning an LCD TV is the energy efficiency of this technology. LCD TVs typically consume 60% lees power than comparably sized tube-type, direct-view TVs.
In most ways that really matter there isn't much difference between LCD TVs and Plasma TVs. Both of these highly popular types of flat panel TVs are thin enough to be placed virtually anywhere, and both produce images that are startlingly clear, sharp, and bright. The most notable difference is screen size. The majority of LCD TVs have a screen size measuring 30 inches and smaller. Plasma TVs are, for the most part, uninhibited by measurement restrictions.
Basically, LCD and Plasma TVs are different approaches to the same result because the both create superior images using radically different technology.