LCD Televisions

LCD- Liquid Crystal Displays have properties of both liquid and solids, so they aren’t really solids or liquids. The solid crystals are heated up to turn them into liquid crystals which are able to display pictures. This makes LCD screens sensitive to changes in temperature.

LCDs use a specific type of liquid crystals called nematic phase. Nematic phase crystals are affected by electric currents, so we are able to manipulate the current through the crystals to create controlled light passage, creating images.

Liquid Crystal Types
Most liquid crystal molecules are rod-shaped and are broadly categorized as either thermotropic or lyotropic. Thermotropic liquid crystals will react to changes in temperature or, in some cases, pressure. The reaction of lyotropic liquid crystals, which are used in the manufacture of soaps and detergents, depends on the type of solvent they are mixed with. Thermotropic liquid crystals are either isotropic or nematic. The key difference is that the molecules in isotropic liquid crystal substances are random in their arrangement, while nematics have a definite order or pattern.

Creating an LCD

There's more to building an LCD than simply creating a sheet of liquid crystals. The combination of four facts makes LCDs possible:

· Light can be polarized. (See How Sunglasses Work for some fascinating information on polarization!)

· Liquid crystals can transmit and change polarized light.

· The structure of liquid crystals can be changed by electric current.

· There are transparent substances that can conduct electricity.

LCD’s use two sheets of polarized glass set at right angles to each other, with liquid crystals and electrode planes in between them.

(A) A Mirror in the back, which makes it reflective.

(B) Piece of glass with a polarizing film on the bottom side

(C) Common electrode plane made of indium-tin oxide on top which covers the entire area of the LCD

(D) Layer of liquid crystal substance

(E) Next comes another piece of glass with an electrode in the shape of the rectangle on the bottom

(F) Another polarizing film at a right angle to the first one.

LCD’s control the intensity of pixels because they can range over 256 shades, which is up to 16.8 million different colors (256 shades of red x 256 shades of green x 256 shades of blue)

The highest resolution LCD screens available are 1024x768. LCD screens of this resolution generally have a few bad pixels because there are 1024 columns by 768 rows, and each pixel has 3 sub pixels (red, green, blue) so there are 2,359,296 transistors total in that type of screen. If just one of those 2.3 million transistors fails there will be a bad pixel on the screen.

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