LED Diode Explained: Types, Applications, and Industry Insights

LED Diode Explained: From Principle to Application

Scientific Foundation of the LED Diode

The LED diode (Light Emitting Diode) is a semiconductor device capable of directly converting electrical energy into light. Its core mechanism is based on the electroluminescence effect of a PN junction. When a forward bias is applied, electrons from the N-region recombine with holes in the P-region. During this recombination, energy is released in the form of photons instead of heat.

The emission characteristics of an LED are determined by the semiconductor material’s band gap. Different band gaps correspond to different photon energies, i.e., different wavelengths of light. For instance:

GaAs (Gallium Arsenide) → infrared emission (850–940 nm)

InGaN (Indium Gallium Nitride) → covers blue and green spectrum

AlGaInP (Aluminum Gallium Indium Phosphide) → efficient red and amber light

GaN (Gallium Nitride) → blue and ultraviolet LEDs

Unlike a conventional rectifier diode whose primary purpose is conduction, the LED belongs to a special type of diode where design goals focus on maximizing external quantum efficiency (EQE) — the proportion of electrons recombining to produce useful photons that escape from the chip.

Main Structures and Packaging of LED Diodes

Since the LED chip is typically only 200–500 µm in size, packaging plays a crucial role in thermal management, light extraction, and mechanical stability.

Through-Hole LEDs

The most classic form is the 3mm or 5mm epoxy-encapsulated LED, widely used for indicators. A typical example is the Kingbright L-934 series, known for low cost and reliability but limited brightness.

SMD (Surface-Mount Device) LEDs

With electronics shifting toward miniaturization, SMD LEDs like 3528, 5050, and 2835 packages dominate in backlighting, displays, and light strips.

COB (Chip on Board)

COB LEDs bond multiple chips directly onto a substrate, then coat them with phosphor, producing high luminous flux density. They are used in downlights, floodlights, and industrial luminaires.

High-Power LEDs

Models such as Cree XLamp XM-L2 and Osram Oslon SSL can deliver hundreds of lumens from a single emitter, suitable for automotive headlights and searchlights. Thermal management is critical for these devices.

Packaging is not only about mechanical assembly but directly impacts light efficiency and device lifetime. Excessive junction temperature accelerates lumen depreciation.

Emission Colors and Corresponding Materials

The emitted color of an LED diode depends on its semiconductor band gap:

Red LEDs: 620–630 nm, based on AlGaInP or GaAsP, widely used in traffic lights and indicators.

Green LEDs: 520–530 nm, earlier realized with GaP, now replaced by InGaN for higher efficiency.

Blue LEDs: 450–470 nm, enabled by GaN. The invention of blue LEDs in the 1990s paved the way for white LEDs.

White LEDs: achieved by coating blue LEDs with yellow phosphor or mixing RGB chips. Nichia first commercialized phosphor-based white LEDs in 1996.

UV and IR LEDs: UV LEDs (365 nm, 395 nm) are used in sterilization and curing, while IR LEDs (850 nm, 940 nm) serve in remote controls and night vision.

Classic LED Models

Several LED diode models stand out as industry benchmarks:

Kingbright L-934 Series → classic through-hole red indicator LEDs.

Nichia 757 Series → SMD white LEDs, widely adopted for general lighting due to long lifetime and high efficacy.

Cree XLamp XM-L2 → a high-power LED capable of >1000 lumens, ideal for headlights and flashlights.

Everlight 2835 LED → mainstream LED strip light component, known for high lumen-to-cost ratio.

Seoul Viosys UV LED (365 nm) → specialized in curing and disinfection applications.

These examples show how different types of diodes within the LED family cater to diverse application requirements.

Comparison with Other Types of Diodes

Although LEDs belong to the diode family, their purpose differs significantly from other types of diodes:

Conventional PN Diode: designed for conduction and rectification, with negligible light emission.

Schottky Diode: optimized for low forward voltage drop and fast switching, widely used in power supplies, unlike LEDs which prioritize photon emission.

Laser Diode: like LEDs, based on PN junctions, but emit coherent light with high brightness, used in communication and optical storage. LEDs, however, emit incoherent, wide-angle light suitable for illumination.

Photodiode: the functional reverse of an LED; instead of emitting light, it detects photons and converts them into current.

This comparison highlights how different types of diodes have distinct design philosophies and application domains.

Application Fields of LED Diodes

1.Lighting

Residential and commercial lighting: LED bulbs, downlights, panel lights

Outdoor lighting: streetlights, tunnel lights, landscape illumination

Automotive: headlights, taillights, daytime running lights

2.Displays

LCD backlighting using white LED arrays

LED video walls (e.g., P2.5, P10 pixel pitch modules)

Next-generation Mini LED and Micro LED self-emissive displays

3.Communication

Infrared LEDs for short-range fiber-optic links

Visible Light Communication (VLC) using modulated white LEDs

4.Sensing and Healthcare

UV LEDs for sterilization, resin curing

IR LEDs for remote controls and surveillance

Blue/IR LEDs in medical therapy and blood oxygen monitoring

Technological Evolution and Future Trends

Mini LED & Micro LED

Mini LED enhances LCD backlight precision with local dimming, while Micro LED represents a disruptive display technology with high brightness and lifetime.

GaN-on-Si Technology

Growing GaN LEDs on silicon wafers promises lower cost and compatibility with CMOS fabrication.

UV LED Expansion

Expected to replace mercury lamps in disinfection and curing, providing eco-friendly solutions.

Smart Lighting Integration

LED diodes combined with sensors and IoT modules enable adaptive and human-centric lighting systems.

Engineering Selection and Comparative Analysis

When choosing an LED diode, engineers should consider:

Wavelength/Color: application-dependent selection of IR, visible, or UV LEDs.

Brightness and Efficacy: measured in lumens or millicandelas.

Power and Thermal Management: high-power LEDs demand metal-core PCBs and heatsinks.

Lifetime: typically over 50,000 hours but strongly influenced by junction temperature.

Cost: through-hole LEDs are the most affordable, while high-power white LEDs are the most expensive.

Compared with traditional light sources, LED diodes offer superior efficiency and durability. For example, generating 1000 lumens requires a 60W incandescent lamp but only about a 10W LED.

From simple indicator lights to advanced display panels and medical sterilization, the LED diode has transformed industries and daily life. As one of the most innovative types of diodes, it redefined the boundaries of semiconductor applications. With ongoing breakthroughs in Micro LED, UV LED, and GaN-on-Si technologies, LEDs are set to expand their dominance in lighting, display, communication, and beyond.

The evolution of the LED diode illustrates how a single type of diode can move far beyond basic rectification to become a cornerstone of modern optoelectronics, illuminating both our devices and our future.