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An introduction to TFT, Monochrome character LCD Displays What is a Liquid Crystal Display LCD? LCD is a broad term that has been used to describe many display technologies and it is often a common belief that a Liquid Crystal Display LCD is the same as CRT (Cathode Ray Tube), LED (Light Emitting Diode) or Plasma displays. However, this is not the case. A Liquid Crystal Display LCD consists of two pieces of glass, with a liquid between two. Think of the Liquid Crystal Display LCD as a window blind. Blinds can be fully closed, so that they block light completely, they can be fully opened allowing all of the light to pass through, or they can be angled allowing only partial light to shine through. Just like a window blind, the LCD does not create its own light, it only blocks or allows light to pass. However, there is one significant difference. An LCD can block light in some areas and in others allow light to pass through. What isn’t a Liquid Crystal Display http://www.focuslcd.com/ LCD? CRT’s, LED’s and TFT LCD Displays (http://www.focuslcd.com/products/standard-displays/tft-lcd-displays/) produce their own light and are referred to as emissive displays. It is because of this that they require more power than a LCD. This makes LCDs more energy efficient. However, a major drawback of the Liquid Crystal Display LCD is that they cannot be seen at night. The solution to this problem is to install a backlight behind the LCD (http://www.focuslcd.com/what-type-of-backlight-to-use-for-an-alphanumeric-lcd-display/). Backlights do require more power than the LCD itself, but they can be turned on only when necessary. Many products that are powered by batteries, like cell phones and watches, have the backlight dim or shut off after a certain amount of time. How does a Liquid Crystal Display LCD work? A picture is worth a thousand words. Take a look at the drawing below. The LCD is built the same as a sandwich. The top of the display contains a polarizer and a glass substrate. There is also a polarizer and a glass substrate on the bottom. Between the two layers is a twisted nematic liquid crystal fluid. The basic structure of the LCD can be seen above. Light passes through the bottom polarizer and then the layer of glass. The light has two options. One, the fluid is rotated to allow the light to pass. Or two, the fluid blocks the light from passing through the front of the glass. What job does the Polarizer on a Liquid Crystal Display LCD perform? The polarizer (http://www.focuslcd.com/what-mode-of-polarizer-to-use-on-a-lcd-display-module/) is an optical filter that allows light waves to pass through in one direction and blocks the light waves in the other direction. It combines the light of mixed polarization into a well-defined focused beam. An example would be the covers for license plates which to make them difficult to read unless you are directly behind the car. What job does the glass substrate on a Liquid Crystal Display LCD perform? The glass contains a substrate with an ITO (Indium Tin Oxide) coating. ITO is a transparent and colorless material, if applied in thin layers. It is used as a coating on the glass because it is transparent, conducts electricity and it acts as a barrier to hold in the twisted nematic liquid crystal fluid. What job does the twisted nematic liquid crystal fluid on a Liquid Crystal Display LCD perform? The twisted nematic liquid crystal fluid is oval in shape. Below is a cross sectional drawing that shows the fluid’s shape. The molecules will rotate to block light or allow it to pass when an electric field is applied. . For additional information on LCD Display technology contact Focus Display solutions at www.FocusLCD.com
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