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Transmissive Mode
Transmissive LCDs are designed to transmit light from the backlight, through the liquid
crystal layer, and out through the front to the eye of the user. This kind of LCD is
the easiest to visualize because there is only one source of light and that light goes
through the components of the LCD in only one direction, from bottom to top in the
sketch below.
Typical Transmissive LCD
The bottom polarizer transmits only light that is polarized in a certain direction. In
each subpixel, the color filter transmits only the polarized light of that subpixel's
color. Most of the backlight's output has been blocked by the time the light reaches
the liquid crystal. When a subpixel is transmitting light, the liquid crystal twists
the polarized light through 270 degrees so that it can pass through the top polarizer.
When an electric field is placed between a row electrode and a column electrode, the
liquid crystal molecules are disrupted from their default spiral configuration so that
they stop twisting the light. The untwisted light is blocked by the top polarizer, so
the subpixel appears dark to the user.
The row and column electrodes must be transparent. Typically they are made of indium
tin oxide (ITO), which is one of the few materials which are both transparent and
conductive. The retardation films improve the appearance of images on the LCD. The
electrodes, glass, and films are designed to be a transparent as they can possibly be,
so that no additional light is lost. The color filter and polarizers are designed to
be as opaque as possible to the wrong kind of light, while being as transparent as
possible to the desired colors and polarizations.
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