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LEDs LED Colour LEDs currently cover a wide range of colour. Their light output and power requirements make them generally many times more reliable and economic to use than incandescent or fluorescent alternatives. To make a LED glow it is necessary to 'forward bias' the diode sufficiently to pass an appropriate amount of current through it. Generally the shorter the wavelength of the light produced, the higher the voltage required for forward bias, and typical forward bias voltages vary from 1.5 to 1.7V for infrared LEDs to 3.3V or more for blue and ultraviolet. The commoner red yellow and green versions require around 2V forward bias and white LEDs about 3.6V.
Notice the considerable difference between the forward voltage (VF) for blue types and red to green types. Blue LEDs also typically have a greater reverse leakage current (IREV) than other LEDs but the safe limit for most LEDs is considered to be around -5V, a VERY LOW value compared with silicon diodes, which may have reverse breakdown voltages measured in tens or hundreds of volts. Therefore LEDs are more easily damaged by relatively small values of either excess forward current, or reverse voltage compared to ordinary silicon diodes, so to take advantage of the LED´s excellent reliability, care must be taken to ensure that any LED operates within its safe operating area. |
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