The term LCD stands for Liquid Crystal Display. The liquid crystal fluid is the active medium that is used to create an image. It consists of a very large number of elongated crystals suspended in a fluid. This reservoir is sandwiched between two thin sheets of glass. Each piece of glass has a transparent conductive pattern bonded to it. See Figure #1 below. The crystals are aligned in a spiral pattern until an electric field is impressed on the conductors.
Figure #1
A sheet of polarizing material is bonded to the outside surfaces of both the front and rear glass covers. As incident light of random polarization enters the top polarizer it is stopped except for that which is polarizerd in the proper direction. With no electric field applied the light is twisted or its polarization is changed by the spiral pattern of the crystals. The bottom polarizer is aligned opposite of the top one but the "twisted" light is now aligned with the bottom polarizer and passes through. The display is now transparent and appears light. See Figure #2.
Figure #2
When an electric field is applied to the conductors the crystals align themselves with that field. The ambient light now passes through the crystal without being twisted. See Figure #3. This makes it out of phase with the bottom polarizer where it is absorbed. The display now looks dark or opaque. By selectively applying the field voltage the desired pattern can be created.
Figure #3
Advances in LCD technology have produced the Super Twisted Nematic (STN) display with a twist angle of >200° vs. 90° for TN type. This results in greater contrast and a wider viewing angle.
