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LED

LED or Light Emitting Diode is a light source device. It releases light when current passes through it. The LED concept is based on a semiconductor device where holes and electrons recombine to produce energy in the form of photons.

The symbol of the LED is shown below:

LED

The need for light-emitting materials comes from the need for the wavelength of radiation. LEDs are used in different applications, such as decorative lights, remote control circuits, etc. Here, we will discuss the invention of the LED, colored LED, types of LED, advantages, etc.

Here, we will discuss the following topics:

Working of an LED

In terms of electronics, LED is defined as a p-n junction diode with an energy gap in the range required for visible light production.

The semiconductor consists of a p junction, n-junction and a neutral region between them. The p-junction possesses majority carriers holes (positive charged), while the n-junction possesses majority carriers electrons (negative charged). It is shown below:

Let's discuss the working of an LED.

Working

When sufficient forward voltage is applied to the p-n junction diode, the majority carries enough energy to move through the neutral region. These electrons recombine with other majority carriers holes. The recombination seems like a particle occupying a high energy state to a low energy state. Thus, it produces electromagnetic radiation. Each time an electron recombines with a hole, electrostatic potential energy converts into electromagnetic energy. The released energy is in the form of photons, as shown below:

LED

Here, forward bias voltage plays an important role. The electrostatic energy applied to electrons and holes should be of the energy gap to produce the desired radiation.

Most of the Light Emitting Diodes operate at low voltages ranging from 1V to 4V. It draws a current between 10mA to 40mA.

Consider the below structure of a LED:

LED

Band Gap

The band gap is defined as the energy difference between the top of the valence band and the conduction band's bottom. The direct band gap is the required band gap for the LED to emit radiations. The photons are emitted at the recombination because there is no transfer in momentum at the time of recombination. Whenever there is some vibration of transfer in momentum, we get a phonon instead of a photon.

A lower band gap between 0.1 and 1.8eV is required for infra-red and far infra-red emissions, whereas a large band gap around 2eV is required to produce visible radiations.

It is difficult to dope the materials with high band-gap energy because such materials have a high melting point. Hence, LEDs have band gap of around 1.6 or 1.8eV.

Components of an LED

A resistor in series is connected with the LED to prevent it from excessive current. It is the concept that is used in most of the projects to prevent it from shattering.

LED

The components of the LED are listed below:

  • Lens
    The lens in an LED is used to evenly distribute the light.
  • LED Chip
    LED chips are the small yellow piece that creates light. It is attached to the piece of metal.
  • Reflective Cavity
    The reflective cavity is the surface cavity that ensures the direction of light. It converges the light to maintain its brightness.
  • Flat Edge
    The flat edge of an LED prevents the leads from twisting. The current passes through the lead that causes the LED to glow. Hence, it is essential to prevent the leads from any twisting.
  • Wire bond
    Wire bonding is an essential part of an LED that connects the LED chips. It also provides an electrical connection between the lead frame and the Light Emitting chips.
  • Semiconductor diode
    The semiconductor diode is a p-n junction material, which is coated with impurities. The impurities excite the electron that causes the LED to glow. The ability of LEDs to become heavily doped is one of the important factors for its wide applications. The material used for the fabrication of LEDs and band gap determines the radiation it can emit. For example, GaAs (Gallium-Arsenic) is used as a material for infrared radiations.
  • Two leads or terminals
    The LED has two terminals called cathode (negative) and anode (positive). The anode is the longer lead, while the cathode is the shorter lead of an LED.

The components of a small LED are quite different from the components of an LED bulb. The LED bulbs can run on low as well as high voltages. The higher the power or voltage, the higher will be the brightness of an LED bulb.

Components of an LED bulb

Let's discuss the components of an LED bulb.

LED
  • Lens

The lens in an LED is used to evenly distribute the light. Sometimes, plastic material is used as the outer lens of an LED to prevent it from damaging.

  • Heat sink and metal
    It is the piece of metal to which an LED is attached. It provides a path for the heat to pass from LED to other elements.
  • LED Chip
    LED chips are the small yellow piece that creates light. It is attached to the piece of metal. Heat passes through the circuit and then cools down, which is known as a heat sink.
    The chip is present on the PCB board. For multiple LEDs, multiple chips are used.
  • Driver
    The circuit board gives signals to LED to change color, ON, OFF, etc. The driver gets energy from the socket. It also prevents the device from any current or voltage fluctuations.
  • Base design
    LED bulbs come with different base designs. It is present at the bottom of an LED.
  • Housing
    The LED requires a housing connection to work. It is generally aluminum-coated plastic housing. It might be a little hot when it touched, but not too hot like fluorescent lighting.

Invention of LED

  • In 1907, Henry Joseph Round (early explorer of the radio) and Guglielmo Marconi (Inventor of the radio) discovered the phenomenon of luminescence when they were working with Silicon-Carbide (A semiconductor that consists of carbon and silicon) and cat's walker detector (an electronic component used in radio receivers). H.J. Round was also the assistant to Guglielmo Marconi.
  • In 1927, a Russian scientist and inventor named Oleg Vladimirovich Losev first investigated and proposed the first LED theory.
  • In 1955, an American Physicist and educator named Rubin Braunstein reported that material such as Gallium Arsenide (GaAs) and other alloys of the semiconductor could emit infrared radiation. He also reported other materials responsible for the infrared emissions, such as Indium Phosphide (InP) and Gallium Antimonide (GaSb).
  • In 1962, an American educator and engineer named Nick Holonoyak, Jr. illustrated the first visible-spectrum LED of the color red. In December, an American electrical engineer named George Craford invented the first yellow color Light-Emitting Diode (LED).
  • In 1976, P Pearsall invented the first LED that has high efficiency and high brightness. At that time, semiconductor materials were introduced, which was suitable for optical fiber communications.

Colored LED

LED's are available in different colors. Let's discuss different colored LEDs and the concept behind their colored lights. The variation in the concentration of phosphors can cause a change in the color temperature. Phosphor is defined as a substance present over a semiconductor die used to display the property of luminescence. The phosphor is responsible for the colored lights in the LED. There are around 16 million shades of LEDs.

So, let's discuss different colored lights and the concept behind their colored lighting.

White LED

White light can be formed in two ways. One way is to produce the three colored lights (Red, Green, and Blue) and combine them. Another way is called Fluorescence, which is defined as a process in which a phosphor coating converts one colored light to another colored light. For example, blue light to white light.

Blue LED

A fluorescent chemical present in the bulb is used to convert the white light into blue light. The chemical is called Gallium Nitride. Blue LED is considered the best light to possess anti-bacterial properties.

Red LED

The material used for red LED lights is called Gallium Arsenide Phosphorus (GaAsP). It is a semiconductor material.

Green LED

Some manufacturers use phosphor material on the blue light to convert it into green light. The phosphor materials are used to convert the high energy spectrum into low energy.

RGB LED

RGB (Red, Green, and Blue) LED is a combination of the three different basic colors LED. Other colors are formed from these three basic colors only. The brightness and intensity of these three colors can be changed to produce a different color.

Color changing LED

Many times, we have seen the same LED lighting with different colors, one after the other. Such LEDs are mostly used for decorative purposes. We must be confused about how a single light can display different colors. The answer is the different materials, which emits photons at a different wavelength. These photons appear as colored lights.

Many times, we have seen the same LED lighting with different colors, one after the other. Such LEDs are mostly used for decorative purposes. We must be confused about how a single light can display different colors. The answer is the different materials, which emits photons at a different wavelength. These photons appear as colored lights.

Some LEDs used different materials that emit photons at a different wavelength, which appears as colored light. All the colors are generated from the three basic colors Red, Blue, and Green.

Let's understand with an example.

Yellow color LED

Two wavelengths of light are combined to produce a different color. The yellow color is a combination of green and red colors. Increasing the amount of red color will form an orange. The amount of colors is changed by varying their intensity.

Applications of LED

We have discussed the components and different colors of an LED. Let's discuss different applications of LED.

  • Decorative Light
    LEDs or multicolor LEDs are used as decorative lights with the two supply wires that can be inserted as a switch when voltage is supplied to the two-wire lead, the different LED lights.
  • Flashlights
    LEDs are widely used as a flashlight in households, industries, etc. It is also present on the front helmet of miners. The working of such flashlights does not require any external supply. These flashlights include battery cells that provide energy to LED to light. We can easily charge these flashlights.
  • Traffic signals
    LEDs come in three basics colors named as Red, Yellow, and Green. These are the ideal color for traffic lights. Such LED colored lights do not require a lens to filter the colors. It is because the colors are accurate for use in traffic lights.
  • Medical Devices
    LEDs are used in various medical devices that are used to treat different medical problems, such as skincare, keratosis, healing wounds, dental, etc.
  • Automotive headlights
    LEDs are used as headlights in different automotive devices, such as cars, bicycles, trucks, etc. It is because of the directional capability of LEDs, which spreads the lights in one direction. It also provides better design, increased safety, and high luminous efficiency.
  • Camera Flashes
    Smartphones and cameras use LED flashes for enhanced photography, even in low light conditions. It means that LED flashes work as artificial light. LEDs as flashes are preferred over other light sources due to low energy consumption, softer, and better illumination.
  • Imaging Inspection
    Automatic Imaging inspection in industries requires continuous and bright illumination. Hence, LEDs are preferred in such applications.
    Many of the scanners use red LEDs for Barcode scanning rather than lasers. LEDs are a compact and reliable source of energy for most industrial applications.
  • Optical Fiber Communications
    The light emitter in Optical fiber is an essential part of the system. Two types of LEDs used in the optical fiber are called Surface Emitting, and Edge Emitting LED. LEDs convert the electrical energy into light energy transmitted between the two ends of the optical fiber.
  • Data Communication
    The use of LEDs can produce high data bandwidth. Due to this reason, VLC was introduced. VLC or Visible Light Communication is a type of data communication that uses visible light for communication. It has replaced the use of radio bandwidth for data transmission.

Differences

Let's discuss some differences between LED, Fluorescent, and Incandescent lights.

LED vs. Fluorescent lights

Initially, fluorescent lights were used as a part of lighting. Nowadays, LEDs have replaced the use of fluorescent light in various applications ranging from households to industries.

Let's discuss some differences between LED and fluorescent lights.

Category LED lights Fluorescent lights
Energy required to produce light Electrical Energy Heat Energy
Power consumption Less More than LED
Life Longer Shorter
Technology inside LED is a solid-state based technology Fluorescent consists of inert gas inside the glass casing
Cost Expensive than fluorescent lights Cheaper than LEDs
Efficiency 50% more efficient than fluorescent lights. Less efficient than LEDs.
UV rays It produces no UV (Ultra-Violet) rays. It produces very few UV rays.

LED vs. Incandescent lights

Here, we will discuss some differences between LED and Incandescent lights:

Category LED lights Incandescent lights
Type of light Diode light Filament light
Energy usage LED uses 75% less energy than incandescent lights. It uses more energy.
Light Output LED requires power around 11 to 12 Watt for light output. Incandescent requires power around 50 Watt for the same light output.
Required bulbs for 25,000 operation hours 1 Around 21
Inert Gas or Vacuum No inert gas or vacuum present in an LED. Incandescent bulbs consist of inert gas or vacuum that is filled inside a translucent glass cover.
Directional LEDs are single directional oriented. Incandescent lights are Omni-directional.
Energy Efficiency Excellent Poor

Advantages and Disadvantages of LED over other light sources

Let's discuss some advantages and disadvantages of LED over other light sources:

Advantages

  • Sizes
    LED comes in different sizes ranging from small to large. The small LEDs can be easily attached to the PCB. Here, PCB stands for Printed Circuited Board. The large LEDs are used in households, industries, etc.
  • Low energy consumption
    Light Emitting Diodes consumes around 75% less energy than fluorescent and incandescent lights. It is because the LEDs are composed of diode lights, while other lights are composed of filament light. Diode light is much more efficient than filament lights.
  • Different colors
    LEDs can emit light of different colors without using any color filters. The most common color of LEDs used is soft white and bright white color light.
  • Longer life
    The life of an LED can last upto ten years, depending on the conditions and usage. It is a long-lasting product with 50 times longer life than incandescent lights and ten times more than fluorescent lights.
  • Less prone to damage
    LEDs are solid-state devices that are very less prone to damage with any external shock.
  • High Intensity
    LEDs have a higher intensity than other types of lights, such as fluorescent, halogen, and incandescent. The higher the current or voltage passes through the LED circuitry, the higher the LED's intensity will be. A resistor in series with LED is used to prevent the LED from the large current.
  • Directional
    Directional means that the LED emits the light in a single direction; The incandescent and fluorescent light sources emit light in all directions. The single or specific directional capability of the LED saves energy and light.
  • Cooling effect
    LED does not emit any radiant heat. It increases the cooling load inside an LED.
  • Improved Safety
    Improved safety of LEDs is one of the essential advantages. All the light sources emit heat, which can sometimes be hazardous. LEDs can effectively operate at low voltages. It emits no forward heat or any polluting radiations. Hence, it is safe to use an LED in households or projects.
  • Different Shapes
    LED comes in different shape styles. We can select an LED as per our requirements.
  • Efficiency
    The efficiency of an LED is much greater than that of incandescent and fluorescent lights. There is no effect of size, color, and shape on the efficiency of an LED.
  • Immediate Illumination
    LED illuminates at its full brightness immediately when the power is switched ON. At the same time, other lights sources take a longer time to illuminate at its maximum brightness.
  • Reliability
    LEDs are much more reliable than other types of light sources. LEDs can withstand vibrations, fluctuations and can also work on colder temperatures. It is due to the absence of fragile parts and filament in an LED.

Disadvantages

  • High cost
    LED has a high cost as compared to other types of light sources. But, there is a continuous drop in prices over recent years. Hence, LEDs have replaced the use of CFL and incandescent bulbs.
  • Winter effects
    LED does not emit heat as compared to other light sources. LED lights used as a signal light do not clear the fog or snow, which may lead to accidents due to these lights' invisibility.
  • Temperature Sensitivity
    The overuse of LEDs in high ambient temperature can fail. To overcome such issues, a heat sink is required. The heat sink is defined as a process to pass excess heat of a mechanical or electronic device to the air or coolant (liquid). It dissipates the excess heat from the device, thus maintaining its temperature.
  • Effect on wildlife
    Some intense blue and white color LEDs can disturb turtle movement on land when used near hatches.





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