Hotdisplay Technology Co.Ltd |
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Two-piece backlight (customized on demand)
LED Backlight
Light Emitting Diode (LED): LED backlights are used primarily for
character modules. They offer a longer operating life - 50,000
hours minimum - and are brighter than Els. They do consume more
power than Els. Being a solid state device, they operate directly
off +5 VDC, so they do not require an inverter. However, a current
limiting resistor is recommended for protection of the LEDs. LEDs
are mounted in an array directly behind the display, which
increases the thickness 4 to 5 mm. LEDs come in a variety of
colors, with yellow-green being the most common.
Cold Cathode Fluorescent Lamp (CCFL): CCFL backlight offers low
power consumption and a very bright white light . Two technologies
are used: direct an edge lighting. In both types a cold cathode
fluorescent tube is the light source. A diffuser distributes the
light evenly across the viewing area. Edge lighting offers a
thinner package and less power. CCFLs require an inverter to supply
the 270 to 300 VAC used by the CCFL tube. They are used primarily
in graphic LCDs and have a longer life - 10,000 to 15,000 hours -
than Els do.
TN STN LCD Panel
LCD:Liquid crystal displays (LCDs) are a passive display
technology. This means they do not emit light nor any radiation;
instead, they use the ambient light in the environment.
By manipulating this light, they display images using very little
power. This has made LCDs the preferred technology whenever low
power consumption and compact size are critical. Liquid crystal
(KLC) is an organic substance that has both a liquid form and a
crystal molecular structure. The rodshaped molecules are normally
in a parallel array, and an electric field can be used to control
the molecules. Most LCDs today use a type of liquid crystal called
twisted nematic (TN) . LCDs consist of two pieces of glass with
transparent electrodes printed on the internal surfaces. An
alignment layer on each glass surface is used to twist the liquid
crystal material in a helical or "twisted" pattern. Polarizers are
used on the outside front and rear surfaces. When the LCD is "off",
no voltage is applied to the electrodes, and light passes through
the LCD.
When it's "on", voltage is applied and the LC molecules align
themselves in the direction of the electric field. This causes the
light to be out of phase with the polarizers and to be blocked,
creating a dark area on the LCD. By selectively applying voltage to
the electrodes, a variety of patterns can be achieved. Many
advances in TN LCDs have been produced. Super twisted nematic (STN)
LC material offers a higher twist angle (240 vs. 90) that provides
higher contrast and a better viewing angle. However, one negative
feature is the birefringence effect, which shifts the background
color to yellow-green and the character color to blue. This
background color can be changed to a gray by using a special
filter. The most recent advance has been the introduction of film
super twisted nematic (FSTN) displays. This adds a retardation film
to the STN display that compensates for the color added by the
birefringence effect. This allows a black and white display to be
produced. Because of the added filtering, FSTN displays look best
when used with a backlight