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Light Emitting Diodes<^< Worksheet: Zener Diodes | Course Index | Transistors >^>  Light emitting diodes (LED's) can be used as general purpose indicators and, compared with conventional filament lamps, operate from significantly smaller voltages and currents. Light emitting diodes are also very much more reliable than filament lamps. Most LED's will provide a reasonable level of light output when a forward current of between 5mA and 20mA is applied. In order to limit the forward current of an LED to an appropriate value, it is usually necessary to include a fixed resistor in series with an LED indicator. The value of the resistor may be calculated from: R = (V - VF) / I where VF is the forward voltage drop of the LED (usually about 2V) and V is the applied voltage. <^< Worksheet: Zener Diodes | Course index | Transistors >^> |