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When backlighting an LCD, the choice comes
really comes down to appearance vs. cost. Each approach has
its advantages and disadvantages, and the method that is right
for for one application may not be right for the next.
The main considerations for
each technology are:
- Incandescent backlights should only used in
non-battery applications. The excessive current draw, along
with the heat generated are the killers. However, when
extremely low cost is a consideration, and current draw is
not an issue, incandescent displays have a home.
- Electroluminescent
backlights are
solid state and have an extremely uniform appearance. They
do, however require an inverter, and the lifetime is
relatively short compared to other solid state methods.
- Fluorescent backlights
are widely used in portable PC's for their low power
consumption for a given light output. They do not work very
well at cold temperatures.
- LED backlights
have extremely long lifetimes, however they are generally
uneven in appearance unless a diffuser is used.
Unfortunately, the diffuser reduces the light intensity,
requiring even more LED's.
- My favorite,
woven fiber optics
are extremely uniform in appearance, and the fiber bundle
can be routed to a position where the bulb can be changed
easily. They are however, somewhat expensive.
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Incandescent -
Incandescent lights are very
bright, however they generate a significant amount of
heat, but
give better performance at very low
temperatures where they act as a heater. They can
provide very white light, but the color can change with
the supply voltage, and they are sensitive to
shock and vibration. The current consumption is very
high, while the price is generally very low. |
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Electroluminescence
- Electroluminescence is a solid state phenomenon
that uses colored phosphors to generate light.
The main advantages to EL backlights are extremely low
current requirements, very low heat generation, and
output uniformity. The biggest drawback to an EL panel is that it
requires an inverter that draws high current
(about 60ma) and takes up board real estate.
The half brightness associated with
EL backlights needs to be taken into consideration for a
reliable long-life design. |
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Fluorescent -
Fluorescent backlights offer very long lifetimes
with low heat and low power consumption. They also require an inverter which draws
relatively high current. The colors do not change
with a slight decrease in supply voltage, and they
can withstand shock and vibration very well. Cold weather
operation is a problem, and appropriate measures should be
taken to avoid cold conditions when using fluorescents.
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LED - The
main advantages of LED backlighting are its long life
along with low cost. The
light provided by LED's tends to be rather uneven, and
if a suitable light pipe or diffuser is used the
lighting can become much more uniform. We can offer a few
tips to help with your diffuser designs to greatly
increase diffusion without sacrificing to much light.
Please call our applications engineering department for
assistance. |
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Woven Fiber Optics
- Fiber optics provides an extremely uniform
backlight, without the need for an inverter. The lifetime
is dependent on the type of bulb used, with LED sources providing 5000 to
100,000 hours. The bulbs themselves are usually mounted
away from the LCD where they can be easily replaced when
necessary. Woven fiber optic panels tend to be very
expensive, but the uniformity and brightness are worth the
extra cost for some applications. |
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