Backlight on device makes key button or LCD glow at dim environment for better
user experience. There are 3 main streams of backlight.
CCFL
? CCFL (cold cathode fluorescent lamp) backlight is usually for large display area
LCD, such as TV LCD monitor, and less use in remote control application. It is
usually in white color.
? It requires the use of an inverter circuit, lightguide, light diffuser sheet and
reflector sheet.
? Use Edge lit method at one side of diffuser (lightguide) and reflect to the LCD
front.
? The incandescent backlight gives high brightness.
? Longer life than EL at about 10-20k hrs., but lose certain brightness at cold
weather.
? The heat generated that need put the CCFL away from the display.
? Since the popularity of LED backlight technology, it is seldom use in products
nowadays.
EL sheet
? Electro-Luminescent sheet is a paper thin material that when powered by a
dedicated inverter glows brightly and remains completely cool.
? It provides an even illumination to the entire glow area while consuming relatively
little electric power, but it requires relatively high AC voltage.
? About 3k –5k hrs. to half brightness.
? For battery-operated remote, this voltage need be generated by a converter
circuit (it may include a EL driver IC or a transformer) and often makes an
audible siren sound when backlight is on.
? The brightness per unit area increases with increased voltage and frequency.
? It can from any cutting shape to match the glow area.
? The normal backlight color is green-cyan but other color is possible. White
color is possible by adding a front pink filter.
? It is less use since LED backlight becomes popular. The main disadvantage of
EL vs LED are:
? Shorter half life, 3k hours vs 50k hours.
? Using AC power circuit while LED use DC.
? It requires larger MOQ as it becomes less popular.
LED
? SMD type LED backlight is popular use in small LCD and keypad.
? It is low cost, longer half life, immunity to vibration, low operational voltage
and simple circuitry, and over 50k hrs. life.
? It is brighter than EL sheet and gives evenly light distributed with optimal light
diffuser and reflector design.
? Two types of configurations: array and edge lit.
? Array lit is putting the LED behind the LCD, or keypad. A diffuser (light guide)
is commonly used for an even light distribution. If no diffuser is used, the
light spot will be seen and result in uneven back light.
? Edge lit is LED put at side of the area to be glow. A diffuser (light guide) and
reflector must be used for reflecting light to the front side.
? As edge-lit technology becomes popular, less LED can be used.
? For LED backlight color costing, red < green < amber < blue < white