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Films and Layers
To display information, an LCD must move and shape light. The end user wants a display which looks good.
A big part of looking good can be quantitized by brightness, contrast and viewing angle. These properties
are greatly improved by the use of various films within the LCD. Below is an illustration of the construction
of a transflective LCD, showing the position of most of the films and layers which are discussed below.
Typical Transflective LCD
Top Polarizer
The top polarizer is fundamental to the light-valve operation of the LCD. It blocks all the light that
isn't properly twisted by a switched-on LCD cell. Kyocera offers top polarizers with several different
surface treatments, as indicated by the code letter at the start of the 3 character suffix at the end
of the Kyocera part number. We use the word "glare" to indicate "non-anti-glare."
| Code |
Polarizer |
New Films |
| A |
anti-glare |
|
| G |
glare |
|
| B |
anti-glare |
anti-reflection |
| H |
glare |
anti-reflection |
| C |
anti-glare |
new scattering film |
| J |
glare |
new scattering film |
| L |
anti-glare |
new scattering film
new retardation film |
Retardation Films
Retardation films essentially bend light. On the backlight side, light which is not perpendicular
to the glass and liquid crystal cells cannot be properly twisted, so it is wasted. The back
retardation film takes in off-angle light and sends it out more perpendicular to the cells.
In reflective operation, the front retardation films gather in off-angle ambient light and make
it more perpendicular to the cells. The front films also work in reverse. They take the perpendicular
output light and send it out at off-angles. This improves the viewing angles or viewing cone of the LCD,
which is good. But the eye of the viewer is at one place, so sending light off in other directions
diminishes brightness in the more perpendicular direction, which is bad. Some trade-off is necessary.
Retardation films also add expense. Kyocera has made design trade-offs believed to be most attractive
to most customers. Customers can also specify semi-custom LCDs with viewing angles and brightness better
suited to their products. Sometimes, special cases of retardation films are called brightness
enhancement films or contrast enhancement films by their vendors, to emphasize their particular
properties.
Scattering Films
In reflective operation, controlled scattering of the light is necessary for a nice appearance of the image.
In a half-mirror transflective LCD, this scattering is best done by a scattering film in front of the liquid
crystal cells.
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