How do you Backlight an LCD ?
There are many choices to consider when backlighting an LCD. Once again the choice comes down to appearance vs. cost vs. features. Each approach has its advantages and disadvantages, and no one method is right for all applications. The data below will only give the highlights of each technology with general comments.
Incandescent - Incandescent lights are very bright, however they generate a significant amount of heat, which can cause problems at high temperatures, but may give better display performance at very low temperatures, where they can act as a heater. They can provide very white light, but the color can change with changing supply voltages, and they can be sensitive to shock and vibration. The current consumption is slightly high, but may not be excessive compared to other options, while the price can be very low. | |
Electroluminescence - Electroluminescence is a solid state phenomenon which uses colored phosphors, not heat, to generate light. The main advantages to EL are extremely low current requirements, very low heat generation, uniformity, and thinness. The biggest drawback to an EL panel is that it requires an inverter which draws relatively high current (50-60ma) and takes up board space. The half brightness (half-life?) problem associated with EL needs to be taken into consideration, however by driving the EL panel at lower than rated voltages, the half-brightness problem can be minimized. | |
Fluorescent -Fluorescent
backlights offer very long lifetimes with low heat generation, and
low power consumption. Like an EL, they also require an inverter which
draws relatively high current. The colors do not change much with a
slight decrease in supply voltage, and they withstand shock and
vibration very well. Cold weather operation can also be a problem, and
should be addressed with the manufacturers. |
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LED - The main advantages of LED backlighting are its low cost and long life. Many different colors are also available. The light provided by LED's tends to be rather uneven, however if a suitable light pipe or diffuser is used, the lighting can become uniform. For operation across a wide temperature range, the forward current supplied to the LED's is critical, and must be varied according to the ambient temperature. | |
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 halogen (which generate high heat) or 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 somewhat expensive, but the uniformity and brightness are worth the extra cost for some applications. |