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Liquid-crystal display

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Lcd.jpg

Liquid crystal displays (LCDs) are a type of electronic display used in digital watches and devices like televisions. LCD televisions are thinner and lighter than cathode ray tube (CRTs) of similar display size, and are available in much larger sizes.

Liquid crystals are a material that exhibited properties of both solid and liquid. It is very reactive to temperature changes, yet very difficult to change states. As a result of its extreme sensitivity to temperatures, it is commonly seen in the word especially in products such as mood rings. More importantly the use of liquid crystal as brought a expedited the advancement of displays. Just a few decades ago people were stuck with large, bulky, power hungry displays. Now thanks to liquid crystals, displays are compact and have far superior quality images. The principle of liquid crystals may appear difficult to understand, but the creation of LCDs actually remains quite simple.

How it Works

Cross-section of a subpixel of a color LCD

Liquid crystals appear to be in a state between solid and liquid, exhibiting characteristics of both. However they more closely resemble a liquid as it requires a great deal of heat to change states. LCDs consist of twisted nematics (type of liquid crystal) that untwist when electrical current is applied. Liquid crystal molecules most often resemble a rod shape. Two oppositely arranged polarized filters are added on both sides of the liquid crystal. Light begins by passing through the first polarizing filter and becomes polarized. The light the travels through the liquid crystal, bending to pass through the second polarized filter. However when electrical current is applied to a liquid crystal, it untwists and prevents light from passing through. [1]

Light starts from the back of the display often with fluorescent tubes that create the light that will display an image. The light from the tubes passes through a white diffusion filter to evenly distribute light. Then the light passes through liquid crystals that are not affected by electricity. The light continues to pass through a color filter to create colorful image. Every display contains often millions of pixels that contain subpixels. Each pixel is made of a red, green, and blue subpixel. Precise control for these three colors can create over 256 colors. Seeing the color yellow on an LCD is actually a combination of red and green. The reason humans see yellow from a combination of red and green is because red and green emit their own wavelength. The human eye sees these two tiny wavelengths on a display and averages them resulting in a yellow (because yellow is between red and green in the color spectrum).[1]

Disadvantages

CRT (Cathode Ray Tube) display, significantly larger and bulkier than a LCD

Despite the fact that LCDs are slimmer, more energy efficient, and display sharper images they do come with disadvantage. The major disadvantage of a LCD compared to a CRT (Cathode Ray Tube) display is dead pixels. LCDs may develop or be manufactured with a nonworking pixel that remains black. CRTs however, do not face this issue as the image is projected on the screen. Another disadvantage of LCDs is the lower response time. CRTs have a faster responce time resulting with a smooth image, unlike some LCDs that have ghosting issues. A major drawback of LCDs is that blacks are still lit, not resulting in a pure black. In CRTs however, blacks actually have no light since CRTs produce an image by projection. In addition CRTs are cheaper to purchase as a result of LCDs.[2]

Currently LCDs are facing LED and Plasma displays as competitors. Compared to LED displays, LCDs cannot produce such as bight picture as LEDs. LCD once again has the worst black level, meaning blacks are not as dark as they are on Plasmas. As a result the image on the LCD has a less vivid image and less depth between blacks and whites. LCDs also create motion blur, unlike Plasmas which don't have this issue. One of the most major drawbacks to LCDs is the inferior viewing angles. Plasma has superior viewing angles, display equally as well from the sides.[3]

History

Older monochrome LCD that displays alphanumeric values

The history of LCDs goes back to the year 1888, in which an Austrian botanist, Friedrich Reinitzer first observed liquid crystals. He shared his discovery with professor Otto Lehmann at the Technical University Karlsruhe of Germany. He noticed the distinct characteristics of both a liquid and a crystal so he proceeded to name it a liquid crystal.[4] Lehmann proceed to publish a work called Liquid Crystals in 1904.[5] Research continues for 80 years before any considerations for applications to products is made. In 1936, the first potentially useful patent is made by The Marconi Wireless Telegraph company.[6] However the biggest breakthrough came in 1962, when Williams Domain experimented by applying electricity to liquid crystals. He was the first to suggest liquid crystals for displays, as his experiments revealed the ability to change with voltage.[4]

Shorty after, scientist George H. Heilmeier joins William on the LCD research.[4] In 1964, Heilmeier had constructed the first functioning LCD.[5] RCA declares their success in developing an LCD in May 1968. In 1969, James Fergason seeks to improve the current LCD which at this time consumed lots of electricity. He discovered the “twisted nematic field effect” which was more effective as a display, consuming less energy and producing better images. He proceeded to patent his discovery in 1971. He opened the International Liquid Crystal Company in which he began manufacturing LCDs. Companies flew to ILIXCO for LCD products such as watches.[4] The first improved LCD manufactured was in 1972. Sales soon skyrocketed with 50% of TVs being LCD by 2008.[6]

Video

Animation about how LCD technology works.

References

  1. 1.0 1.1 Tyson, JeffHow LCDs Work HowStuffWorks. Last accessed 3 June 2015. Unknown Author
  2. LCD vs CRT Pros and Cons Bootstrike. Last accessed 3 June 2015. Unknown Author
  3. LED LCD vs. plasma vs. LCD Bootstrike. Last accessed 3 June 2015. Unknown Author
  4. 4.0 4.1 4.2 4.3 Invention History of Liquid Crystal Display (LCD) Circuits Today. Web. Last updated November 5, 2013. Unknown Author.
  5. 5.0 5.1 Television History and Facts Ait Pro. Web. Last updated 9 August, 2010. Unknown Author.
  6. 6.0 6.1 Brief History of LCD Tresna. Web. Last accessed June 1, 2015. Unknown Author.