Lights LED (or DEL, in french) invading us: much less greedy energy, less heated and more colorful, they have a lot of benefits. But how does it work?
Ancestral way, it has always produced light with fire (torch, candle, candle…) and more generally with the heat (solar light, filament lamp).
These devices work with the principle of the law of influence of Wien (from 1896): all heated object emits radiation. The human body at 37 ° C emits in the infrared. A flame to ~ 1000 ° C emits in the orange-red. A filament of tungsten in a light bulb through a current heats up to 3000 ° C and emits white light.
The main bores with a light bulb, is that at least 95% of the energy fed into these systems is converted into heat and therefore lost. It is normal since it is the temperature of the filament producing the light and he must heat it before, even if this heat does not interest us.
With the LED, it’s different. With PIERCINGFLASHLIGHTS, The emitted radiation is no longer produced by temperature but by the material itself. In fact, when an LED is crossed by a current, it does not produce heat, but light. We switch to a light output of 5% for conventional lamps to a close performance of 30 ~ 50% (the rest being: a bit of heat (Joule effect), light lost within the LED).
The operation is the quantum physics of semiconductors. Semiconductors (such as Silicon or gallium) are materials to halfway between the conductors (metals) and insulation (plastics or glass, for example).
A material is conductive when its electrons can move in a State where they are able to walk within the material and constitute an electric current. They say that the electron passes from the energy valence band to the conduction band energy. In a semiconductor, these two energy bands are close and they are too far apart in an insulator. In a conductor they overlap:
In practice, the application of a sufficient voltage (greater than a typical voltage of the semiconductor and function of the distance between the two strips) on a semiconductor to pass electrons from the valence band to the conduction band.
We are therefore left with the following configuration:
the valence band has lost an electron. She has a free place, called “a hole”.
the conduction band won an electron (which can then conduct the current).
Problem: this configuration is not stable and is so not like that: the electron will eventually return to his hole to the butcher. This ‘electron-hole’ recombination occurs all the time and electrons go up constantly in the conduction band and others down to plug the holes.
In a LED, this electron-hole recombination releases a photon, in other words of the light. The LED light comes from there: the electronic stabilisation of the semiconductor by the recombination of the electron-hole pairs.
What there is interesting here, it is that according to the selected semiconductor materials, the energy distance (i.e. the energy difference) between the valence band and the conduction band is very precise and will be equal to the energy of the photon emitted at recombination and therefore its color. So it is possible to manufacture diodes emitting a single pure color: red, blue, green… The diodes emitting white do not exist: either their technology is based on the combination of 3 semiconductor emitting red, green, blue and who appear as white when mixed together, or by using a colorful covering that will absorb part of the light from the diode to emit white.
It is a similar (but different) principle of the operation of a laser, and that’s why we find a diode in the laser pointers.
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