What is an LED? Complete Guide to LED Technology

LEDs, or Light-Emitting Diodes, are semiconductor electronic devices that produce visible light when an electrical current passes through them. Originally developed as simple indicator lights, LEDs have evolved into the preferred technology for indoor and outdoor commercial and industrial lighting applications.

Image credit: Wikimedia Commons

The electronic symbol below represents an LED, showing the cathode, anode, and direction of light emission:

Brief History of LED Development

LED technology dates back to the early 1900s when British physicist Henry Round discovered that silicon carbide crystals could produce light when an electrical current was applied. In 1962, GE scientist Nick Holonyak developed the first practical visible light LED, which produced red light. George Craford later developed yellow LEDs.

Early LEDs cost approximately $200 per diode. Advances in manufacturing and materials science have reduced costs dramatically while improving efficiency and light output.

How LEDs Work: The Science Behind the Light

LEDs operate using a P-N junction within semiconductor material. The LED contains an anode and cathode separated by a crystal of semiconductor material. Adding specific impurities creates P-N electronic junctions within the LED chip. The assembly is enclosed in a plastic housing that serves as a lens to direct the light output.

Schematic diagram of LED internal structure (Image credit: Wikimedia Commons)

When voltage is applied across the electrodes, current flows from the anode (P side) to the cathode (N side). When an electron meets a hole at the P-N junction, it falls to a lower energy state. The energy difference between these states, called the “band gap,” determines the characteristics of light produced.

The excess energy is released as a photon. A larger band gap creates higher energy differences and shorter wavelengths of emitted light.

The electromagnetic spectrum shows that red light has the longest wavelength (700 nm) while violet has the shortest (400 nm). LEDs produce light in narrow wavelength bands. Phosphor coatings are often used to create broader spectrum white light. Multiple LEDs can be combined on circuit boards to produce custom wavelengths and full-spectrum lighting.

LED Device Components and Construction

Several factors contribute to LED lighting efficiency improvements:

• Advanced materials with optimized band gaps
• Improved fabrication techniques, reducing costs while increasing efficiency
• Enhanced heat dissipation methods
• Better light extraction from semiconductor materials
• Phosphor technology improvements for wavelength conversion

Individual LEDs are small components that produce specific amounts of light based on their design. LEDs are classified as low-power, mid-power, or high-power devices. Multiple LEDs must be combined to achieve the desired light output levels.

This compact size enables flexible LED combinations and versatile lighting designs. Circuit board design determines whether individual LEDs or LED groups fail independently, making simultaneous failure of all LEDs highly unlikely.

Complete LED Light Assembly

While individual LEDs can be assembled manually, manufactured LED products offer superior performance through matched components, optimized integration, and professional aesthetics.

LED lighting products contain these essential components:

LED Cluster: Multiple LEDs arranged to produce the required light output.

LED Drivers: Convert alternating current (AC) to direct current (DC) and regulate current flow to LEDs. LED drivers typically output 12V or 24V, though other voltages are available. Quality drivers include:

• Driver integrated circuits
• Control circuitry (electrical control gear)

Important: While resistors can provide voltage reduction, they create inefficient voltage drops and may allow excessive current that can damage LEDs. Professional-grade LED drivers provide proper current regulation.

Thermal Management: Critical for LED Performance

Heat Sinks: LEDs and driver electronics generate heat that must be dissipated to maintain performance and lifespan. Poor thermal design or excessive drive currents cause overheating, leading to reduced light output and shortened LED life.

Three Essential Thermal Management Elements

Substrate Material: Metal core PCBs provide mechanical mounting while spreading heat over larger areas for efficient transfer to heat sinks.

Interface Materials: Thermal films or compounds transfer heat while providing electrical isolation between active components and passive heat sinks.

Heat Sinks: Two types are available:

• Active heat sinks: Use fans for forced air circulation
• Passive heat sinks: Use metal fins and airflow design for natural convection

Modern passive heat sink designs handle most applications effectively. Active cooling may be necessary only when multiple high-power LEDs operate in confined spaces.

LED Optics and Light Control

Optics: LEDs produce directional light with standard distribution angles of 120-180 degrees into the upper hemisphere. Various beam patterns are available, including narrow spot, wide flood, and specialized distributions.

Lenses control viewing angles through:

• Primary optics: Built into LED packages
• Secondary optics: Additional lenses for precise beam control

Polycarbonate lenses offer excellent optical transmission with minimal light loss and cost-effective manufacturing. Precise surface quality and accurate shaping ensure uniform light distribution and maximum efficiency.

Key Advantages of LED Technology

• Energy Efficiency: Commercial LED lighting typically produces 100-130 lumens per watt, with laboratory demonstrations exceeding 200 lumens per watt under ideal conditions. This efficiency surpasses incandescent and fluorescent technologies. Energy savings typically allow LED lighting to pay for itself within 1-3 years, depending on usage patterns and local energy costs.
• Extended Lifespan: LED lights typically last 30,000 to 100,000 hours, with most commercial products rated for 50,000+ hours. This translates to 10-30 years of operation, depending on daily usage hours. Extended life reduces maintenance costs and makes LEDs ideal for difficult-to-access locations.
• Superior Operating Characteristics: LEDs operate effectively in low temperatures and are unaffected by frequent on-off cycling. This makes them safer and more efficient than traditional lighting in cold environments and applications requiring frequent switching.
• Shock Resistance: LED components are isolated from external surfaces through quality insulation. Electrodes are embedded within the device matrix and driver electronics are protected within housings. Interface materials between LEDs and heat sinks prevent current leakage.
• Vibration Resistance: Unlike incandescent bulbs with suspended filaments, LED electrodes are encased in solid materials, making them highly resistant to vibration and impact.

Choosing the Right LED Solution

Understanding LED technology helps in selecting appropriate lighting solutions for specific applications. Consider factors such as required light output, operating environment, thermal management requirements, and desired beam patterns when specifying LED lighting systems.

Professional Installation Note: LED driver installation and electrical connections should be performed by qualified electricians in accordance with local electrical codes and safety requirements.