- Can be made very thin (<0.3mm)
- Flat and fully flexible (when applied to a flexible plastic substrate)
- Have a wide viewing angle
- Give off very little heat when emitting light
- Can be made at low cost
- Can operate over a wide temperature range (-40ºC to +70ºC).
- Can be made in low volumes using simple techniques
What is EL?
Electroluminescence (EL) is the emission of light under electric-field excitation
A typical EL display consists of many light emitting phosphor-ceramic elements, each sandwiched between a conductive electrode, where one of the electrodes is transparent, allowing light to escape.
The light emitting component is phosphor, usually a zinc sulphide (ZnS) powder doped with manganese (Mn). Silver (Ag), or graphite loaded screen printable inks, and indium tin oxide (ITO), a transparent conductive metal, are used as the electrodes.
An a.c. voltage is applied to the electrodes, causing the phosphor to rapidly charge and discharge, the current excites the manganese ions, resulting in the emission of light during each cycle.
Driving EL lamps and displays
Modern thick film EL is driven using an alternating current (AC). Nominal voltage and frequency for EL lamps is 110 Volts and 400 Hertz (Hz), however current EL display operation is not tied to these values.
Phosphor EL can be dc-driven by low voltage circuits (1.5-5V) by using inverters and inductors to generate the necessary a.c. voltages of 100V to 300V (peak to peak) at frequencies of 50 to 2,000 Hz. These EL devices can generate luminances of 10-500cd/m2. Specific lamp/driver arrangements will deliver a lamp half-life of between 700hrs and 10,000hrs.
Varying the operating voltage and frequency controls the brightness, and to some degree the colour of the EL light emitting element.
For example, increasing the voltage increases lamp brightness, whereas increasing the frequency will increase lamp brightness and shift the colour slightly toward the blue. However, increasing voltage and frequency will reduce lamp life.
EL has traditionally been used for backlighting LCD displays (e.g. watches, mobile phones, etc.) and car and aircraft instrument panels.
