Light-emitting diode

A light-emitting diode (LED) is a semiconductor device that emits light when an electric current passes through it. LEDs are used in a wide range of applications, from indicator lights to displays and general lighting.

Principle of Operation

LED circuit symbol

An LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence.

The color of the light (corresponding to the energy of the photons) is determined by the energy band gap of the semiconductor. LEDs are available in a wide range of colors, including red, green, blue, and white.

History

The first practical visible-spectrum LED was developed in 1962 by Nick Holonyak while working at General Electric. Early LEDs emitted low-intensity infrared light, but modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

Original blue LED

The development of blue LEDs in the 1990s was a significant breakthrough, leading to the creation of white LEDs by combining blue LEDs with phosphors.

Types of LEDs

Standard LEDs

Standard 5mm green LED

Standard LEDs are used as indicator lights on electronic devices and are available in various sizes and colors. They are typically low-power devices.

Surface-Mount LEDs

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Surface-mount LED

Surface-mount LEDs are designed for use on printed circuit boards (PCBs) and are used in applications where space is limited. They are commonly used in modern electronic devices.

RGB LEDs

RGB LED spectrum

RGB LEDs contain red, green, and blue LED chips in a single package. By adjusting the intensity of each chip, a wide range of colors can be produced. RGB LEDs are used in displays and decorative lighting.

High-Power LEDs

High-power LEDs are used in applications requiring high brightness, such as flashlights, automotive lighting, and general illumination. They require heat sinks to manage the heat generated during operation.

Applications

Indicator Lights

LEDs are widely used as indicator lights in electronic devices due to their low power consumption and long life.

Displays

Blue LEDs on a proto-board

LEDs are used in displays, including seven-segment displays, dot matrix displays, and full-color displays such as those used in televisions and computer monitors.

Lighting

LEDs are increasingly used in general lighting applications due to their energy efficiency and long lifespan. They are used in residential, commercial, and industrial lighting.

Specialty Applications

LEDs are used in a variety of specialty applications, including infrared LEDs for remote controls, ultraviolet LEDs for sterilization, and grow lights for plants.

Advantages

LEDs offer several advantages over traditional light sources, including:

• Energy efficiency: LEDs consume less power than incandescent and fluorescent lights.
• Long lifespan: LEDs can last for tens of thousands of hours.
• Durability: LEDs are solid-state devices and are more resistant to shock and vibration.
• Compact size: LEDs can be made very small, allowing for use in a wide range of applications.

Challenges

Despite their advantages, LEDs also face challenges, such as:

• Heat management: High-power LEDs require effective heat dissipation to maintain performance and lifespan.
• Initial cost: LEDs can be more expensive upfront compared to traditional lighting.

Related Pages

• Semiconductor
• Electroluminescence
• Photodiode
• Light bulb
• Organic light-emitting diode