The display consists of two polarizing transparent panels and a liquid crystal solution sandwiched in between. The screen's front layer of glass is etched on the inside surface in a grid pattern to form a template for the layer of liquid crystals. Liquid crystals are rod-shaped molecules that bend light in response to an electric current; the crystals align so that light cannot pass through them. Each crystal acts like a shutter, either allowing light to pass through or blocking the light. The pattern of transparent and dark crystals forms the image.
LCD televisions use the most advanced type of LCD, known as an "active-matrix" LCD. This design is based on thin film transistors (TFT) which are, basically, tiny switching transistors and capacitors that are arranged in a matrix on a glass substrate. Their job is to rapidly switch the LCD's pixels on and off. In a colour LCD television, each color pixel is created by three sub-pixels with red, green and blue colour filters.
An important difference between plasma and LCD technology is that an LCD screen does not have a coating of phosphor dots (colours are created through the use of filters). That means you will never have to worry about image burn-in, which is great news, especially for anyone planning to connect a PC or video game system. LCD televisions are extremely energy-efficient, typically consuming 60% less power than comparably-sized tube-type direct-view televisions.
Older models of these televisions had a delay problem called "ghosting". As the pixels were not able to change colour instantly, fast moving objects left a trace on the screen. Newer models have decreased this delay to 8 milliseconds (recently 4ms), so unless you have a very large screen (more than 40"), the delay is not noticeable at all. Another problem of these screens is the black level. In order for the black colour to show on the screen, the back light must be completely blocked. This poses a problem as there is always a small amount of white light leaking from the narrow space between pixels. So most LCD televisions have difficulty going completely “black” and instead of showing black, a very dark grey is shown. Contrary to manufacturers’ claims, LCD televisions have a limited viewing angle. So at 170 degrees you will see “a picture” but it is not of high quality. Moreover, if you want to use your television as a computer monitor, it is advisable to buy an LCD television that has a computer input, not an LCD monitor that has a television tuner; as the latter acts as a very poor quality television whilst the former introduces good quality in both applications.
Nowadays almost all LCD televisions are high-definition televisions (HDTVs). This means that they are compliant with the recently-approved ATSC standard in North America. There are different resolutions available for LCD televisions. They include: 480p, 480i, 720p, 1080p, 1080i, and 2160p. These are the number of horizontal lines the television can display and the letter that follows shows the type of scan used to refresh the display (interlaced or progressive, for details see CRT televisions). In 480 models, the resolution is about the same as CRT televisions, although they are not called high definition anymore. In 720p models the resolutions that are supported include 1,024×768, 1,280×720, and 1,366×768. In 1080i models the resolution that is supported is 1280×1080 and in 1080p models resolution 1,920×1,080 is supported. In 2160p models, 3,840×2,160 is supported which is even higher than ATSC standard.
Technically speaking, all of these numbers are accurate and useful, but do not put too much stock in them. In the real world, it is difficult to tell the difference between native resolutions once you get into high definition. An important factor is the number of pixels the LCD can support which is dependent on its physical size. For example, a 37" LCD with "only" 1,366×768 pixels has to throw away a good deal of information to display a 1080i picture and there is really no way for you to see more details on a similar 37" LCD with 1080 resolution. This used to be the case when there was a huge price difference between 1080 and 720 versions of LCDs with the same size, but nowadays 1080p native resolution is so common among high definition televisions that you should not even consider it as a factor in your purchasing decision.
No comments:
Post a Comment