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The viewing angle is the angle formed on either side of the viewing
direction (or bias angle),
where the contrast of the display is still considered acceptable. The term
"viewing angle" is often used erroneously with the term "viewing direction"
or "bias angle".
Liquid Crystal Displays have a limited
viewing angle. They lose contrast and become hard to read at some viewing
angles and they have more contrast and are easier to read at others. The
size of the viewing angle is determined by several factors, primarily the
type of Liquid Crystal Display fluid and the duty cycle. Because the viewing
angle tends to be smaller than most people would like, certain viewing
direction (or bias angle) is designed into the module at the time it is
manufactured. This means the nominal viewing angle is offset from the
perpendicular by some amount. Several versions of the LCD module are then
offered with this bias set to different angles or positions to accommodate
as many applications as possible.
An STN
character display running at a duty cycle of 1/16 has a viewing angle of ±20
degrees, and a bias angle of 25 degrees. For this example, assume the
display is a 12:00 (top viewing) type. When the display is viewed from 25
degrees above the vertical, it will have its maximum contrast and best
“look”. If the viewer moves his eye further above the display by an
additional 30 degrees, he will see the display reduce in contrast (but still
be easily readable). Moving the viewing position any further above the
display will reduce its contrast to an unacceptable degree.
Contrast Adjustment and Viewing Angle
Adjusting the contrast voltage, VO, will effect the viewing direction (bias angle) to some
extent, but not the viewing angle. 12:00 display can be optimized for a 6:00
viewing position by adjusting the contrast voltage. A 12:00 display set for
6:00 viewing position will not have as great a contrast as a 6:00 display
set for 6:00 viewing position, and vice versa. Designers often want a
display to be optimized for straight-on viewing. Either a 12:00 or a 6:00
module can be used; and the contrast voltage can be adjusted slightly to
optimize the display for that viewing position. In the example used above,
the viewing angles of both the 6:00 and 12:00 modules actually overlap the
perpendicular (or straight on) viewing position.
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