Typical forward voltage values of standard LEDs at a current-limited value of 20mA. Roughly 2V are developed across them when passing a useful forward current Figure 2 lists the typical forward volt drops (Vf) of different colored standard 5mm diameter LEDs at forward currents of 20mA.įIGURE 2. LEDs are pn junction diodes, usually made from gallium arsenide (GaAs) or aluminum-gallium arsenide (AlGaAs) types of semiconductor materials, and emit light when stimulated by a forward current.
Standard LED symbol, together with its terminal notations. LED BASICS INTRODUCTIONįigure 1 shows the standard symbol that is used to represent an LED in this article, together with its basic anode (a) and cathode (k) terminal notations.įIGURE 1. A variety of such circuits are shown in this article.
LEDs have typical power-to-light energy conversion efficiencies some 10 to 100 times greater than a simple tungsten filament lamp and have very fast response times (less than 0.1µS, compared to 10s or 100s of milliseconds for a tungsten lamp), and are thus widely used as visual indicators and as simple ‘flashing light’ units.
The most widely used of all optoelectronic devices is the simple LED (light emitting diode), which emits a fairly narrow bandwidth of visible (usually red, orange, yellow, or green) or invisible (infrared) light when its internal diode junction is stimulated by a forward electric current.
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