How LEDs work?

We can find a lot of different LED lamps today in the market. Event Ikea is selling them now. You can find them in many colors, even control them using your iPhone! They’re cheap, very energy efficient and durable. LED is awesome, but how does it work?

 

The technology is not new. It was out there for decades, however the great achievement that allows to substitute classic incandescent lights with modern LED lamps is a more intense light power and the ability to emit white light. This is achieved using blue leds with a phosphor coating that absorbs part of the blue light and produces yellow light throug fluorescence.

LED stands for Light-Emitting Diode. This type of diode is achieved basically with a PN junction: the union of two semiconductor materials, one with positive charge (P) and one with negative charge (N).

In semiconductors atoms are bond through covalent bonds, but when its temperature is increased, some electrons get free and can conduct electricity. This is possible because the bond on those electrons is very weak. When the electron leave its place, the remaining empty space is called hole.

In order to create a positive or negative charged semiconductor some impurities can be introduced in the material.

led

PN junction: P side, with positive charge have holes and N side has plenty extra electrons. When current is applied electrons will fill the holes emitting light in the process.

If we introduce an atom with 5 electrons in its external layer, the additional electron will be lightly bond in the molecule at ambient temperature, and it will move around in order to conduct electricity. In this case 4 electrons of the atom introduced will fill the holes, making the material negative charged, because it have free electrons but not holes.

However, if the impurity introduced have 3 atoms in its outer layer, the material will get positive charged at ambient temperature.This material will have many holes that needs an electron to be complete.

Now we have that clear, let’s talk about PN junction. It’s an structure formed by two near structures, one P and one N, and it’s a fundamental part of many devices like diodes.
This junction allows the current to be conducted in a direction but not in the other, this is one of the characteristics of diodes but I won’t cover that in this article. I’ll post a video at the end that covers this is more detail if you want to understand it better.

When the two materials are put very close, it’s enough to apply right amount of electric current in order to make the electrons from the negative charged semiconductor flow to the positive charged semiconductor and fill its holes. When a hole is filled, the recombination generates energy in form of light energy. Pretty cool huh?

The advantage of LEDs in comparison to incandescent lights are many. For example, the incandescent light requires that the filament warms up in order to emit light, so a big part of energy is wasted as heat. Also a good part of the light spectrum in incandescent bulbs is in an ultraviolet range, so it can’t be used for illumination, cutting to about in half the efficiency of the light generation. Also the led is an electronic component, very small and made of solid materials and can easily be used in an electronic circuit. This makes easier the computarized control of the light. The good part is that it’s also possible to generate almos every visible spectrum of light (colors) on demand.

N. Gentile

Software engineer, science lover. Collaborated in several European Space Agency (ESA) projects and European Commission scientific R&D projects mainly related to earth observation. Currently working in video-game behaviour forecasts for one of the most influential companies of the industry.

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