The Facts

• There are two types of LCDs -- passive and active. Passive LCDs are one image that cannot be changed. Active LCDs are the more common type. Active LCDs are used in digital watches, computer screens, camera view screens and television screens.
  
  

History

• Liquid crystals were discovered by Friedrich Reinitzer in 1888, according to nobelprize.org. Up until that time, there were only thought to be three states of matter -- liquid, solid and gas. When Reinitzer heated a crystal, he discovered that at certain temperatures, it had characteristics of both liquid and solid crystal.
  In 1991, Pierre-Gilles de Gennes won a Nobel prize for his work with liquid crystals in the 1960s. It was his work that established the knowledge needed to develop modern LCD devices.
  
  

How it Works

• In a LCD, liquid crystals are wedged between two plates of glass, according the Gale Encyclopedia of Science. As electric currents pass through the glass, they manipulate the positions of the liquid crystals inside. As the crystals change orientation, the light that passes through them changes amount, color and direction. This is how active images move across the screen.
  
  

Considerations

• When purchasing an LCD device, consumers should keep a few things in mind.
  LCD screens have limited viewing angles, unlike the more classic Cathode Ray Tube designs of old TVs and computer screens. Consumers should walk around display screens, checking the visibility of different angles.
  The contrast ratio is the degree of difference between the blackest black and the whitest white. The contrast ratio is especially important when visiting dark Web sites on a computer or watching dark scenes in a movie. If the screen has a low contrast ratio, it will be difficult to see what is going on in the scene.
  
  

LCD vs. Plasma

• Plasma screens are LCD screens' main competitors today. Unlike LCD screens, which subtract colors from the spectrum of white light, plasma screens are made up of thousands of pixels that are filled with gas. When electricity hits each pixel, it lights up the correct color.
  Plasma screens, like LCD, are used for TVs and computer monitors. Plasma screens generally have a better picture than LCD. screens in low light, but their more reflective surfaces can create glare in bright light.