LED DIODE

The diode led differ, from all the other semi­conductor, for the capacity to emit light when they are polarizes  directly and  crossed  from current. The same acronym with which they are designates , in fact, it means this: Light Emitting Diode, that is, diode emitter  of light. More in a generalized manner, the diode  led is an element that belongs to the world of the optelectronic, that it is that special branch of the electronics that alloy together the phenomena electrical workers with the optical.
The led   is constructed like a normal diode, with semiconductor material  and has one junction of type P-N. But in this case, they are not use the germanium or the silicon, but a compound of gallium, that it characterizes the nature of the emission that is wanted to be achieved. For example. in order to have a light pertaining to the spectrum of the infrared, use of the arseniuro  of gallium. In any case, the colors more common  are the red, the yellow, the green and the orange.  
In order to totally take advantage of the phenomenon of the light emission, the  semiconductor junction to of the led is realized in much thin shape, to the scope of being transparent and to concur the escape of the ray luminous. Also the container of the diode must carry out this function, therefore to times it is equipped of concentric disc or diffusing cap.  
The practical advantages,  introduced in the electronic circuits from the diode led, if compared with the duties entrusted to the light bulbs, can be reassumed shortly in the following points:

1° - Miniaturization

2° - Low energy consumption

3° - Fast answer in frequency

4° - Limitless duration

 Every led , in order to turn on  itself, needs of the minimal value of voltage. That red, that it is most common, demands at least 1,5 V. But this voltage can easy be derived from  local dc power source. In every type of use of the led, instead, these must be connect in series with a resistor, otherwise would be covered from one current of destructive intensity.  
The brightness emitted from the led is proportional to the current that crosses it, second the famous law of Ohm:

I = V alim : R

However, the intensity of current, that it crosses the led, does not have to exceed the order of grandezza for which the component has been planned. And if a range of values is wanted to be cited, it can be asserted that the led they are constructed for being crosses from currents comprised between  5 mA  and  20 mA .  

 Fig. 1 - On the left the symbol is brought back, adopted in the composition of the theoretical circuits, of the  led. To right its more common real expression, with the two indicating arrows of the precise position of the cathode electrode (k): heel-guide and terminal them longer.