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LCD Backlighting

2018/11/20 Viewers:

Light Emitting Diode, or LED, backlight is the most popular backlighting for small and medium LCDs. The advantages of LED backlighting are its low cost, long life, immunity to vibration, low operational voltage, and precise control over its intensity. The main drawback is it does require more power than most of the other methods, and this is a major drawback if the LCD size is large enough. LED backlights come in a variety of colors, with yellow-green being the most common, and now white is becoming cost effective and very popular. LED backlights offer a longer operating life - 50,000 hours minimum - and are brighter than ELPs. Being a solid state device, they are configured to operate with typically a +5VDC power (and optionally 12VDC power), so they do not require an inverter.


The LED backlight has two basic configurations; Array and edge lit. In both types the LEDs are the light source that are focused into a diffuser that distributes the light evenly behind the viewing area. In Array lit configuration there are many LEDs mounted uniformly behind the display, it offers more uniform and brighter lighting and consumes more power. In Edge lit configuration, the LEDs are mounted to on side (typically the top) focused edge on into the diffuser, it offers a thinner package and consumes less power.


Electroluminescence Panel (ELP) Backlighting

Electroluminescence Panel, or ELP, is a solid state phenomenon which uses colored phosphors, not heat, to generate light. EL backlights are very thin, lightweight and provide an even light. They are available in a variety of colors, with white being the most popular for use with LCDs. While their power consumption is fairly low, they require voltages of 100 VAC @ 400Hz. This is supplied by an inverter that converts a 5, 12 or 24 VDC input to the AC output. Information about these inverters can be found in the Power Supply section of our website. ELPs also have a limited life of 3,000 to 5,000 hours to half brightness. The biggest drawbacks to an EL panel is that it requires an inverter to generate the 100VAC, consistent brightness, and limited life.



Cold Cathode Fluorescent Lamp (CCFL) Backlighting

Cold Cathode Fluorescent Lamp, or CCFL, backlights offer low power consumption and a very bright white light. The primary CCFL configuration used in LCD backlighting is edge lighting. A cold cathode fluorescent lamp is the light source with a diffuser distributing the light evenly across the viewing area. CCFLs require an inverter to supply the 270 to 300 VAC @ 35KHz used by the CCFL tube. Information about these inverters can be found in the Power Supply section of our website. They are used primarily in graphic LCDs and have a longer life - 10,000 to 20,000 hours - than ELPs do. Their biggest drawbacks are: cold weather will reduce the light output by as much as 60% (see graph below), they require an inverter to generate the 350VAC (please note that the inverters do not function well at low temperatures), the light intensity cannot be varied (it is either on or off), and vibration can reduce the life expectancy of up to 50%.


Woven Fiber Optic Mesh Backlighting

Woven Fiber Optic Mesh backlighting provide 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 up 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.


Incandescent Backlighting

Incandescent Lamp backlighting is only used where cost is a major factor. While Incandescent lights are very bright, they are not uniform, generate a significant amount of heat (which can cause problems at high temperatures), have short life spans, and use significant power for the brightness achieved. They can provide very white light, but the color can change with changing supply voltages, and they can be sensitive to shock and vibration.