Light Emitting Diode - Meaning, Principle, Uses, Types, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 04:31 PM IST

A light-emitting diode is a device that emits light in the presence of an electrical current. Thanks to their energy efficiency and extended service life, LEDs have altered the way people light their homes and other structures and even the streets. In practice, they are present within the displays of smartphones and even in traffic light systems showing their significance in the present-day technology.

Light Emitting Diode - Meaning, Principle, Uses, Types, FAQs

What is LED?

LED stands for Light Emitting Diode and it is a device which emits light by flowing a current to the positive-negative junction like a semiconductor laser. It emits various wavelength lights in the ultraviolet, visible and infrared regions, corresponding to its band gap energy.

LED circuit diagram

LED symbol and LED diagram (LED circuit diagram)

In circumstances where traditional circuits, such as a standard diode are employed, the LED also have a specified voltage drop forward. The voltage drop is determined by the LED's current, the colour of the light generated and other factors. The voltage drop varies between 1.5V and 2.5V for currents ranging from 10 to 50 mA.

Principal of LED

The LED is connected in the forward bias, which allows the current to flow in the forward direction. The flow of current is caused by the movement of electrons in the opposite direction. The recombination shows that the electrons move from the conduction band to the valence band and they emit electromagnetic energy in the form of photons. The energy of photons is equal to the gap between the valence and the conduction band. The energy is released in the form of heat in conventional LED diode workings. However, with an LED, the release of energy in the form of photons would result in the emission of light energy. The process is referred to as electroluminescence.

How much energy is discharged in the form of light in an LED is determined by the forbidden energy gap. As a result, the light colour and visibility cannot be altered based on its wavelength. By doping the light with various contaminants, the colour and wavelength of the light emitted may be determined.

Related Topics

Working of LED

LED is nothing but a diode made of semiconductors having a $\mathrm{P}-\mathrm{N}$ junction. LED is based on the phenomenon of recombination of electrons with holes. When the LED is forward biased, the electrons from the N -region cross the P - N junction and recombine with the holes existing in the P -region. For the electrons to recombine with holes existing in the P-region, they must give some of their energy. When recombination occurs, the recombining electrons release energy in the form of heat and light.

Working of LED

What determines the colour of an LED?

The colour of an LED is determined by the material used in the semiconducting element. The two primary materials used in LEDs are aluminium gallium indium phosphide alloys and indium gallium nitride alloys. Aluminium alloys are used to obtain red, orange and yellow light, and indium alloys are used to get green, blue and white light. Slight changes in the composition of these alloys change the colour of the emitted light.

Uses of LED

LEDs are used in a variety of industries, such as optical communication, alarm and security systems, remote-controlled operations, robotics, and so on. Because of its long-lasting capability, low power needs, quick response time, and fast switching capabilities, it uses LED in a variety of applications. The following are some of the standards that LED adheres to:

Backlighting for televisions
Frequently seen in exhibits
Applied to automobiles
LEDs are utilised in light dimming.

NEET Highest Scoring Chapters & Topics

This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.

Download E-book

What Determines an LED's Colour?

The colour of an LED is determined by the energy band gap of the semiconductor material used to make the LED. The energy band gap is the difference in energy between the valence band and the conduction band of a semiconductor material. LEDs made of different semiconductor materials with different energy band gaps will emit light of different colours.

For example, red LEDs are made of gallium arsenide (GaAs), which has a relatively small energy band gap. Blue LEDs are made of gallium nitride ( GaN ), which has a relatively large energy band gap. White LEDs are typically made of gallium indium nitride (GalnN), which has an energy band gap that can be tuned to emit different colours of light. White LEDs are also made using a combination of different coloured LEDs.

NCERT Physics Notes:

Types of LED

Gallium Arsenide (GaAs) is an infrared semiconductor.
Red to infrared, orange Gallium Arsenide Phosphide (GaAsP).
High-brightness red, orange-red, orange, and yellow Aluminium Gallium Arsenide Phosphide (AlGaAsP).
Gallium phosphate (GaP) comes in three colours: red, yellow, and green.
Green Aluminium Gallium Phosphide (AlGaP).
Green, emerald green gallium nitride (GaN).
Near-ultraviolet gallium indium nitride (GaInN) — bluish-green and blue.
As a substrate, Silicon Carbide (SiC) is blue.
Blue Zinc Selenide (ZnSe).
AlGaN (Aluminium Gallium Nitride) – ultraviolet.

LEDs have a wide range of shapes sizes and colours. The colour of the plastic lens is frequently, but not always, the same as the colour of the light emitted. Infrared LEDs, for example, are frequently made of purple plastic, whereas most blue gadgets have colourless housings.

LED diode working

Advantages and Disadvantages of LEDs

Advantages of LEDs
1. LEDs are small-sized and can be assembled to form numeric and alphabet displays.
2. LEDs are environmentally and economically friendly.
3. LEDs are rugged and can-, therefore, withstand shocks and vibrations.
4. LEDs can be operated in a wide range of temperatures.
5. The switching time of the LED (both on and off) is less than one. So, they are very suitable for the dynamic operation of many arrays.

Disadvantages of LEDs
1. The drawbacks of LEDs are that they get damaged by overvoltage or overcurrent.
2. They have wide optical bandwidth compared to LASER ( $=10 \mathrm{~nm}$ ).
3. Their temperature depends on the radiant output power and wavelength.
4. LEDs are not suited for large-area displays, primarily because of their high cost. For larger displays, devices using gas fillers are used.

Frequently Asked Questions (FAQs)

1. What is the duration of a light emitting LED diode working?

The rated life of many LED is up to 50,000 hours. This is roughly 50 times longer than an incandescent bulb, 20-25 times longer than a halogen bulb, and 8-10 times longer than a CFL bulb. A 50,000 bulb will survive more than 11 years if uses of LED 12 hours a day.

2. What is the principle of operation of a light emitting LED diode working?

Principle of Operation: A light-emitting diode (LED) is a semiconductor light source with two leads. When triggered, it is a p–n junction diode that emits light. Electrons are able to recombine with electron holes within the device when a proper voltage is given to the leads, releasing energy in the form of photons.

3. What are some of the drawbacks of LED lighting?

Drawbacks of LED lighting are:

High setup costs.
Compatibility with transformers
Colour shift throughout lamp life is a possibility.
Standardization of performance has not yet been streamlined.
Overheating can shorten the life of a lamp.

4. What is the power consumption of LED?

A light bulb's electricity consumption is measured in KWh. Over the course of a 15,000-hour lifespan, an LED bulb consumes 127.5KWh. Incandescent bulbs that are uses of LED for 15,000 hours (theoretically; incandescent bulbs do not last that long) consume 900KWh of electricity.

5. What is the purpose of a light emitting LED diode working?

LED (Light emitting LED diode workings) transform electrical energy directly into light, as opposed to traditional light sources that convert electrical energy into heat and subsequently into light, resulting in efficient light creation with minimal electricity waste.

6. How do LEDs behave when reverse biased?

When reverse biased, LEDs typically do not conduct current or emit light. However, if the reverse voltage exceeds the LED's breakdown voltage, it can cause damage to the device.

7. How do organic LEDs (OLEDs) differ from traditional LEDs?

OLEDs use organic compounds that emit light when an electric current is applied. Unlike traditional LEDs, OLEDs can be made into flexible, thin sheets and can produce light from a larger area, making them suitable for displays and lighting panels.

8. How do high-power LEDs differ from standard LEDs?

High-power LEDs are designed to handle higher currents and produce more light than standard LEDs. They often have better heat dissipation mechanisms and are used in applications requiring bright illumination.

9. What is the efficiency of LEDs compared to other light sources?

LEDs are generally more efficient than most other light sources. They can convert up to 70% of their energy into light, compared to incandescent bulbs (10%) or fluorescent lights (20%).

10. What is the significance of the band gap in LED operation?

The band gap of the semiconductor material in an LED determines the energy of the photons emitted, and thus the color of the light. Materials with larger band gaps produce higher-energy photons, resulting in shorter wavelengths (bluer light).

11. Can LEDs produce white light?

Yes, LEDs can produce white light. This is typically achieved by using a blue LED with a yellow phosphor coating, or by combining red, green, and blue LEDs (RGB LEDs).

12. What is the difference between through-hole and surface-mount LEDs?

Through-hole LEDs have long leads that can be inserted through holes in a circuit board, while surface-mount LEDs are flat and designed to be soldered directly onto the surface of a circuit board. Surface-mount LEDs are smaller and better suited for compact designs.

13. How do RGB LEDs work?

RGB LEDs contain three separate LEDs (red, green, and blue) in one package. By controlling the intensity of each color, a wide range of colors can be produced through color mixing.

14. What is an LED driver, and why is it used?

An LED driver is a power supply designed to regulate the current flowing through an LED or string of LEDs. It's used to ensure consistent brightness and protect LEDs from current fluctuations that could damage them or reduce their lifespan.

15. What is the forward voltage drop across an LED?

The forward voltage drop across an LED typically ranges from 1.8 to 3.3 volts, depending on the semiconductor material and the color of light emitted. Red LEDs have lower voltage drops, while blue and white LEDs have higher drops.

16. Why are LEDs more energy-efficient than traditional light bulbs?

LEDs are more energy-efficient because they convert a higher percentage of electrical energy directly into light, with less energy lost as heat. Traditional bulbs waste a lot of energy as heat.

17. What is the typical lifespan of an LED compared to traditional light bulbs?

LEDs typically have a much longer lifespan than traditional bulbs. While incandescent bulbs last around 1,000 hours, LEDs can last 25,000 to 50,000 hours or more, depending on the quality and usage.

18. How do LEDs compare to other light sources in terms of environmental impact?

LEDs generally have a lower environmental impact than other light sources. They contain no mercury, use less energy, and have a longer lifespan, reducing waste. However, the production process and disposal of LEDs still have some environmental considerations.

19. What is the difference between indicator LEDs and illumination LEDs?

Indicator LEDs are typically low-power devices used for signaling or display purposes, while illumination LEDs are higher-power devices designed to produce enough light to illuminate spaces or objects.

20. What is LED binning, and why is it important?

LED binning is the process of sorting LEDs based on their characteristics like color, brightness, and forward voltage. It's important for ensuring consistency in LED performance, especially in applications where color matching is critical.

21. What is a Light Emitting Diode (LED)?

A Light Emitting Diode (LED) is a semiconductor device that emits light when an electric current passes through it. It's a type of diode that converts electrical energy into light energy through a process called electroluminescence.

22. How does current flow through an LED?

Current flows from the anode (positive terminal) to the cathode (negative terminal) in an LED when it's forward biased. Electrons move from the n-type region to the p-type region, where they recombine with holes.

23. Why do LEDs require a current-limiting resistor in most circuits?

LEDs require a current-limiting resistor because they have a very low internal resistance. Without a resistor, the LED would draw excessive current, potentially damaging or destroying it.

24. How do LEDs behave at different temperatures?

LED performance can vary with temperature. Higher temperatures generally reduce LED efficiency and lifespan. Some LEDs may also experience a slight color shift at different temperatures.

25. What is thermal runaway in LEDs, and how can it be prevented?

Thermal runaway occurs when an increase in temperature causes an increase in current, which further increases temperature, potentially damaging the LED. It can be prevented by using proper heat sinking and current regulation.

26. How does an LED differ from a regular diode?

While both are semiconductor devices, an LED is designed to emit light when forward biased. Regular diodes don't emit visible light and are primarily used to control current flow in circuits.

27. What is the basic principle behind LED operation?

LEDs operate on the principle of electroluminescence. When electrons in the semiconductor recombine with electron holes, they release energy in the form of photons (light). This occurs in the depletion region of the p-n junction when the LED is forward biased.

28. Why do LEDs only emit light when forward biased?

LEDs emit light only when forward biased because this condition allows electrons to flow from the n-type region to the p-type region, where they recombine with holes and release energy as photons. Reverse bias doesn't allow this electron flow and recombination.

29. What determines the color of light emitted by an LED?

The color of light emitted by an LED is determined by the band gap energy of the semiconductor material used. Different materials have different band gaps, resulting in the emission of different wavelengths (colors) of light.

30. What are the main components of an LED?

The main components of an LED include the semiconductor chip (die), anode and cathode leads, a reflector cup, and an epoxy lens or encapsulation.

31. How do LEDs contribute to energy conservation?

LEDs contribute to energy conservation by using less electricity to produce the same amount of light as traditional sources. Their long lifespan also reduces the energy and resources needed for manufacturing and replacing light sources.

32. What are some common applications of LEDs?

LEDs are used in various applications including general lighting, displays, traffic signals, automotive lighting, backlighting for LCD screens, indicator lights in electronics, and in optical communication systems.

33. How do LEDs perform in cold temperatures compared to other light sources?

LEDs generally perform well in cold temperatures, often better than in warm conditions. Unlike fluorescent lights, which can struggle to start in cold weather, LEDs reach full brightness almost instantly in cold environments.

34. What is the relationship between LED brightness and current?

LED brightness is directly related to the current flowing through it. Increasing the current increases the brightness, but only up to a point. Exceeding the LED's maximum current rating can damage it or reduce its lifespan.

35. How do LEDs contribute to the Internet of Things (IoT)?

LEDs play a crucial role in IoT devices as indicators, in displays, and in smart lighting systems. Their ability to be easily controlled and their low power consumption make them ideal for battery-operated and networked devices.

36. What is pulse-width modulation (PWM) in LED control, and why is it used?

Pulse-width modulation is a technique used to control LED brightness by rapidly switching the LED on and off. The human eye perceives this as dimming. PWM is used because it's more energy-efficient than simply reducing current and helps maintain color consistency.

37. How do LEDs compare to laser diodes?

While both emit light, LEDs produce incoherent light over a range of wavelengths, while laser diodes produce coherent, monochromatic light. Laser diodes typically require more precise current control and have a narrower emission angle.

38. What is the importance of heat management in LED design?

Proper heat management is crucial in LED design because excessive heat can reduce efficiency, alter color output, and shorten the LED's lifespan. Heat sinks and thermal management systems are often incorporated to dissipate heat effectively.

39. How do LEDs contribute to light pollution reduction?

LEDs can help reduce light pollution because they can be more precisely directed than traditional light sources. Their ability to be easily dimmed and controlled also allows for more efficient and targeted lighting, reducing unnecessary illumination.

40. What is color rendering index (CRI), and why is it important for LEDs?

Color rendering index is a measure of how accurately a light source reveals the colors of objects compared to natural light. It's important for LEDs, especially in applications where color accuracy is crucial, such as in retail lighting or photography.

41. How do LEDs enable new form factors in lighting and display design?

The small size, low heat output, and directional nature of LEDs allow for innovative designs in lighting fixtures and displays. They enable thin, flexible, and uniquely shaped lighting solutions that weren't possible with traditional light sources.

42. What is the difference between direct and indirect LED lighting?

Direct LED lighting aims light directly at the area to be illuminated, while indirect LED lighting bounces light off surfaces like walls or ceilings. Indirect lighting can create a softer, more diffused light with less glare.

43. How do LEDs impact circadian rhythms and human health?

LEDs, particularly those with adjustable color temperature, can be used to mimic natural light patterns throughout the day. This can help regulate circadian rhythms, potentially improving sleep patterns and overall well-being.

44. What are quantum dot LEDs, and how do they differ from traditional LEDs?

Quantum dot LEDs use tiny semiconductor particles called quantum dots to produce light. They can produce more saturated colors and a wider color gamut than traditional LEDs, making them particularly useful in display technologies.

45. How do LEDs enable Li-Fi technology?

Li-Fi (Light Fidelity) uses LEDs to transmit data by rapidly modulating the light output. The high switching speed of LEDs allows for fast data transmission, potentially providing an alternative or complement to Wi-Fi in certain applications.

46. What is the role of LEDs in horticulture and plant growth?

LEDs are used in horticulture to provide artificial light for plant growth. They can be tuned to specific wavelengths that promote photosynthesis and other plant processes, allowing for efficient indoor farming and greenhouse lighting.

47. How do LEDs contribute to automotive safety and design?

LEDs in automotive applications provide brighter, more energy-efficient lighting for headlights, taillights, and interior lighting. Their fast response time improves safety in brake lights, and their small size allows for more creative and aerodynamic vehicle designs.

48. What is the concept of LED efficacy, and how is it measured?

LED efficacy refers to the amount of light produced per unit of electrical power consumed, typically measured in lumens per watt (lm/W). It's a key measure of LED efficiency and is important for comparing different lighting technologies.

49. How do LEDs enable adaptive lighting systems?

The ability to easily dim LEDs and change their color temperature allows for adaptive lighting systems that can adjust to ambient light conditions, time of day, or user preferences. This can enhance comfort, productivity, and energy efficiency in various environments.

50. What are the challenges in developing UV LEDs, and what are their applications?

Developing efficient UV LEDs is challenging due to material limitations and heat management issues. However, UV LEDs have important applications in sterilization, water purification, curing processes, and medical treatments.

51. How do LEDs contribute to the development of micro-LED displays?

Micro-LEDs are extremely small LEDs that can be used to create high-resolution, high-brightness displays. They offer advantages in contrast, response time, and energy efficiency compared to other display technologies, potentially revolutionizing screens in various devices.

52. What is the role of phosphors in white LED production?

Phosphors are materials used to convert the light from a blue or UV LED into white light. They absorb some of the LED's light and re-emit it at longer wavelengths, creating a broad spectrum that appears white to the human eye.

53. How do LEDs enable dynamic architectural lighting?

The controllability, color-changing capabilities, and compact size of LEDs allow for dynamic architectural lighting. Buildings can change their appearance, create moving light patterns, or respond to environmental conditions, enhancing urban aesthetics and creating interactive spaces.

54. What are the challenges and benefits of using LEDs in street lighting?

LED street lighting offers benefits such as energy efficiency, long lifespan, and better light control. Challenges include initial cost, potential glare issues, and the need for proper heat management. However, the long-term energy savings and reduced maintenance often outweigh these challenges.

55. How do LEDs contribute to the development of flexible and wearable electronics?

The small size, low heat output, and low power requirements of LEDs make them ideal for flexible and wearable electronics. They can be integrated into fabrics, thin films, or flexible substrates, enabling innovative designs in wearable displays, smart clothing, and health monitoring devices.