Light Emitting Diode (LED)

An LED is made up of semiconductors, materials that can either conduct or insulate electricity depending on the conditions. The semiconductor material is typically doped to create two regions:

• A negatively charged N-type region that has excess electrons.
• A positively charged P-type region where electrons are missing and left with “holes”.

The two types are connected to form a PN junction. The electrons from the N-side move to the P-side, and holes from the P-side move to the N-side. During this process, a new region is formed at the interface, called the depletion layer. A PN junction, when enclosed in a protective casing and has external leads for electrical connections, forms a PN junction diode.

When an external battery is connected across the diode such that the positive terminal is connected to the P-side and the negative terminal to the N-side, electric current flows through the circuit. The electrons from the N-side and holes from the P-side move, recombine and release energy in the form of photons, which produce visible light. This process is known as electroluminescence.

The energy band gap of the semiconductor material governs the energy required to move electrons and holes across the device. It is defined as the difference in energy between the valence band (where holes are normally present) and the conduction band (where electrons can move freely). 

When the electrons recombine with holes, the energy difference is released as light, and the color (wavelength) of that light depends on the size of the band gap. The larger the band gap, the higher the energy of the emitted photons, which corresponds to a shorter wavelength of light (towards the blue end of the spectrum). A smaller band gap results in lower energy photons, leading to longer wavelengths (towards the red end of the spectrum). 

LED efficiency and versatility are partly due to the wide range of colors they can produce. By precisely controlling the material composition, manufacturers can create LEDs that emit light across the visible spectrum and beyond, including ultraviolet and infrared regions. The following table shows common materials used in LEDs, the range of light wavelengths they emit, and their corresponding colors.

• Energy Efficiency: Uses significantly less power than incandescent and fluorescent bulbs, converting more energy into light and less into heat​
• Long Lifespan: Can last up to 25 times longer than traditional light bulbs, reducing replacement costs and waste​
• Eco-Friendliness: Contains no harmful substances like mercury (found in some fluorescent lamps) and is fully recyclable.​
• Durability: Is highly resistant to shock, vibration, and impact, making it suitable for harsh environments​
• Low Heat Emission: Emits very little heat compared to other light source, reducing the risk of burns
• Instant Illumination: Lights up instantly without a warm-up time, providing immediate brightness​
• Flexibility in Design: Is available in various shapes, sizes, and colors, allowing for creative and customized lighting solutions​
• Directional Lighting: Emits light in a specific direction, making it ideal for applications like task lighting and reducing the need for reflectors​

• Consumer Electronics: Used for backlighting in LCD screens (smartphones, TVs, laptops) and as an indicator on devices like routers, remote controls, and appliances
• Automotive: Used for headlights, taillights, daytime running lights, interior lighting, and dashboard displays in vehicles.
• General Lighting: Used for residential bulbs, downlights, streetlights, floodlights, and outdoor signage, providing efficient illumination for both indoor and outdoor environments​
• Architectural Lighting: Used for accent lighting in homes, offices, and public spaces, as well as decorative and display illumination for landmarks, events, and public art​
• Displays and Advertising: Used in digital billboards, signs, video walls, and scoreboards in stadiums, providing high-visibility and dynamic displays for advertising and public information
• Industrial Applications: Used for factory illumination, machine vision systems, and indicator lights in control panels, ensuring reliable operation and efficient monitoring in industrial environments​
• Transportation: Used in traffic signals, railway indicators, aviation lighting, and marine navigation systems, ensuring clear communication and safety in various transportation sectors​
• Specialized Uses: Used as a grow light for agriculture and horticulture, promoting plant growth, as well as for water purification and disinfection, offering efficient, eco-friendly solutions for both agricultural and environmental application