What is LED (Light-Emitting Diode)?

An LED (Light-Emitting Diode) is a semiconductor device that emits low-spectrum inconsistent light when the PN joint is directly polarized and an electric current passes through it.

What is LED (Light-Emitting Diode)? Features & How Does It Work?

The color depends on the semiconductor material used to make the diode and can vary from ultraviolet and visible to infrared.

Ultraviolet light-emitting diodes are called UV LED (Ultraviolet Light), and infrared light-emitting diodes are called IRED (InfraRed Emitting Diode).

History

The first LED was developed by Oleg Vladimirovich Losev in 1927, but it was not used in industry until the 1960s.

LEDs had low light intensity only in red, green, and yellow colors, and it was possible to control them on and off with a remote control.

At the end of the 20th century, ultraviolet and blue LEDs were invented, leading to the development of the white LED, a phosphor-coated blue light LED that produces yellow light.

White LEDs are like moonlights, providing high brightness and expanding the use of lighting systems.

How Does LED Work?

The operation of LEDs occurs in semiconductor materials when an electron loses energy as it moves from the conduction band to the valence band.

This lost energy can manifest as a displaced photon with a random amplitude, direction, and phase.

Whether the energy lost when an electron moves from the conduction band to the valence band emerges as an independent photon or some other form of energy will depend mainly on the type of semiconductor material.

When a semiconductor diode is directly biased, p-region holes move to the n-region, and n-region electrons move to the p-region.

Both displacements of charges create current flowing through the diode.

If electrons and holes are in the same region, they can recombine, meaning the electrons grab the holes that have fallen from a higher energy level to a more stable lower level.

This process usually emits a photon indirect band gap or direct band gap semiconductors with energy corresponding to the band gap.

This does not mean that there is no photon emission in other semiconductors.

However, these emissions are more likely to occur in indirect bandwidth semiconductors than in indirect bandwidth semiconductors.

Therefore, spontaneous emission does not occur significantly in all diodes and can only be seen in diodes such as visible light LEDs.

It has a special constructive arrangement to prevent radiation from being reabsorbed by the surrounding material and the energy of the forbidden band corresponding to the visible spectrum.

In other diodes, energy is released primarily in the form of heat, infrared radiation, or ultraviolet radiation.

If the diode releases energy in the form of ultraviolet radiation, it absorbs the ultraviolet radiation emitted by the diode.

It produces visible radiation through fluorescent or phosphorescent substances that then emit visible light.

The semiconductor device is encapsulated in a plastic cover that is more durable than the glass typically used in incandescent lamps. Although plastic can be colored, it does not affect the color of the light emitted.

An LED is usually a composite light source with different parts, so the intensity pattern of the emitted light is quite complex.

The LED current should be chosen well to obtain a good light intensity.

For this, it must be taken into account that the operating voltage varies from approximately 1.8 to 3.8 volts, and the range of current that must circulate through it varies according to its application.

Typical values ​​of the direct polarization current of the current LED are between 10 and 40 mA.

In general, LEDs have better efficiency. Therefore, the lower the current passing through them, the more optimized their operation is, usually a compromise between the light intensity and efficiency they produce.

The first LED emitting in the visible spectrum was developed by General Electric engineer Nick Holonyak in 1962.

OLED Technology

In direct current (DC), all diodes emit a certain amount of radiation when electron-hole pairs recombine.

In short, when electrons drop from the conduction band to the valence band, they emit photons in the process. As a result, its color will depend on the height of the tape, that is, on the materials used.

Silicon or germanium diodes emit infrared radiation far beyond the visible spectrum. However, with unique materials, visible wavelengths can be achieved.

LEDs and IREDs have unique geometries to prevent the emitted radiation from being reabsorbed by the material surrounding the diode itself.

The first diodes discovered were red-colored and infrared diodes, and further technological developments allowed diodes to be made.

In particular, in the late 1990s, Shuji Nakamura developed blue diodes. By adding the previously developed reds and greens and their combination, he obtained white light.

The zinc selenide diode can also emit white light by mixing the blue light it radiates with the red and green light created by photoluminescence.

The latest innovation in the field of LED technology is ultraviolet diodes, which are successfully used to produce black light to illuminate fluorescent materials.

Both blue and ultraviolet diodes are expensive compared to the most common and are, therefore, less used in commercial applications. Typical commercial LEDs are designed for 30 to 60 mW of power.

In 1999, diodes that could operate with 1 watt of power for continuous or daily use were introduced to the market.

These diodes have much larger semiconductor matrices to withstand such powers and incorporate metal fins to dissipate the heat generated by the Joule effect.

Today, LEDs are being developed and used in various areas with much superior performance and lighting applications.

Nichia Corporation developed white light LEDs with a luminous efficiency of 150 lm/W using 20 milliamperes (mA) of direct polarization current.

This efficiency is higher than other light sources in terms of performance alone, as it is high chromatic and approximately 1.7 times greater than a fluorescent lamp and approximately 11.5 times greater than an incandescent lamp.

Its efficiency is even higher than that of the high-pressure sodium vapor lamp, which is considered one of the most efficient light sources.

At the beginning of the 21st century, the development of OLED diodes made of organic semiconductor polymer materials began.

Although the efficiency achieved with these devices is far from that of inorganic diodes, their production aims to be much cheaper than them.

It is also possible to add large amounts of diodes to any surface using painting techniques to create color displays.

OLED (Organic Light-Emitting Diode) is a diode based on an electroluminescent layer formed by a film of organic components that responds to a particular electrical excitation that spontaneously produces and emits light.

OLED-based technologies do not only have an application as image reproduction displays.

The advantages of this new technology are enormous, but it has a number of disadvantages, although many of them are purely situational.

Hybrid Lighting Systems are a technological solution that aims to take advantage of the high efficiency of typical LEDs and the low costs of OLEDs.

The Cyberlux company projects two examples of such a technological solution under the names HWL (Hybrid White Light) and HML (Hybrid Multi-Color Light). As a result of these studies, much more efficient and cost-effective lighting systems can be produced.

In Which Areas Do We Use LED Technology?

Infrared diodes have been used in remote controls for television systems, air conditioning equipment, musical equipment, all remote control applications, and device detectors since the mid-20th century.

It is also used to transmit data between electronic devices such as computer networks and devices such as mobile phones and handheld computers. Although this data transmission technology is older than Bluetooth technology, we can say that it is still used today.

LEDs are widely used in all kinds of status indicators in signaling devices and information panels.

They are also used to illuminate liquid crystal displays for cell phones, calculators, electronic diaries, bicycles, and similar uses.

In addition, it is also used in laser printers that are frequently used in office applications and serve as documentation.

LED lighting has excellent advantages. It has many benefits, such as reliability, greater energy efficiency, outstanding resistance to vibrations, better visibility in different lighting conditions, less energy dissipation, less risk to the environment, and the ability to operate continuously.

LEDs can produce different colored lights with high luminous efficiency, unlike most lamps used so far that have filters to achieve a similar effect.

White Light LEDs are a very well-established attempt to replace existing bulbs with much more advantageous devices.

Technology is available today that consumes 90% less than standard household incandescent bulbs and 40% less than most fluorescent lights.

Additionally, these LEDs can last up to 20 years and cost less than traditional fluorescent bulbs.

LEDs are also used in the emission of light signals transmitted through fiber optics.

The LED display is a very bright display consisting of rows of green, blue, and red LEDs arranged according to RGB architecture, individually controlled to create very bright and vivid images with very high contrast.

Compared to others in LED displays, it gives good color support, extremely high brightness, and the ability to be fully visible in sunlight.