LCD backlighting

LED backlight is the most popular backlighting for small and medium LCDs. 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. The LED backlight has two basic configurations; Array and edge lit. 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 focused edge on into the diffuser, it offers a thinner package and consumes less power.

LED features

-          Low operational DC voltage, does not require an inverter.

-          Longer operation life time 50,000 hours minimum.

-          Low cost, immunity to vibration

LED 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. 

CCFL backlight offers 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 at high frequency used by the CCFL lamp.

CCFL backlights are used primarily in graphic LCDs and have a longer life - 10,000 to 20,000 hours - than EL backlights do.  Their biggest drawbacks are: cold weather will reduce the light output by as much as 60% , 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%.

 

EL (Electroluminescence) backlight has very uniform brightness, but brightness is low and it is used for small size LCD (<4”). No heat generated. Very compact (EL thickness 0.2~0.6mm).

EL Drawbacks is backlight flicker due to noise from the circuit, short life time 5000hrs, brightness is lower than LED or CCFL, an inverter is required.

 

   
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