Light Emitting Diodes (LED) Information

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Last revised: November 18, 2024

Reviewed by: Scott Orlosky, consulting engineer

Light emitting diodes (LEDs) are PN junction devices that give off light radiation through electroluminescence when forward biased. They are used as various indicators in aviation, automotive and traffic lighting, as well as lighting for lamps, flashlights, even streetlights and stadium lighting. Most light emitting diodes function in the near infrared and visible ranges, and the range has been extended UV, now, as well.

LEDs Compared to Other Light Sources

LEDs have a number of advantages over other legacy lighting sources such as incandescent and fluorescent bulbs. The efficiency of LEDs is greater than incandescent bulbs and unlike fluorescent bulbs, it is independent of size and shape. LEDs turn on and off quickly, can be easily dimmed by modulation or current reduction, and can easily be cycled on and off. They emit very little heat in the form of IR and heat waste is channeled through the base rather than the bulb. They are also resistant to shock, fail slowly over time, and have a much longer lifetime (approximately 40,000 hours) than fluorescents (approximately 12,000 hours) or incandescent (approximately 1,500 hours).

There are certain disadvantages to LEDs however. LEDs tend to cost more than conventional lights. The voltage sensitivity of LEDs requires series resistors or current-regulated power supplies to prevent current overload. Performance of LEDs is also largely dependent on temperature. Excessive heat from the environment or heat generated internally can damage or degrade the diode, shortening its life if not mitigated via the use of heat sinks. The light quality of LEDs is also considered inferior. A standard incandescent light has a Color Rendering Index (CRI) from 95 to 100%. LED’s by comparison are closer to 80%. The CRI is a measure of how faithfully it can produce the desired wavelength, which affects the apparent color rendering of the environment it illuminates.

Specifications

When selecting a diode, industrial buyers should consider:

Wavelength or light color
Forward current and voltage
Optical power and luminous intensity
Type of Construction
Viewing angle
Color temperature
Available power sources
Lens type

The wavelength or color is usually one of the most important criteria when selecting an LED. The wavelength emitted by the diode can be within the visible, infrared, or ultraviolet spectrum. Multicolored LEDs can emit a range or number of different wavelengths. It is important that the color of an LED is appropriate for its intended use, since different applications involve different colors or types of light.

Forward Current and Voltage — LEDs operate at a rated current and voltage, usually within a certain range. For LEDs, voltage is normally measured in volts (V) and current is measured in milliamps (mA). If a system supplies a predetermined voltage to the system, it is important to select an LED designed with those specifications. Since current overload is a main cause of LED failure, it is important to correctly match this specification and provide any necessary current regulators.

Optical power and luminous intensity are important performance specifications for LEDs. Optical power is the energy output of the LED, usually measured in milliwatts (mW) because LEDs require less power than other light sources. Luminous intensity is the amount of light an LED can put out, usually measured in milliCandelas. Luminosity and power become more important in the selection of larger LEDs in applications where more light is required.

LEDs can function in different ways depending on the type of construction.

Edge emitting LEDs have outputs that emanate from between the heterogeneous layers. They have relatively small beam divergence, allowing for more efficient fiber coupling than surface-emitting LEDs. They allow for higher data rates in optical fiber communications.
Surface emitting LEDs have a thin active layer parallel to the surface from which the light is extracted. They emit light perpendicular to the active region.
Super luminescent LEDs (SLDs) are a variation of edge emitting LEDs. They are based on stimulated emission with amplification but insufficient feedback for oscillation to build up. SLDs are applied in situations where a smooth and broadband optical spectrum (i.e. low temporal coherence), combined with high spatial coherence and relatively high intensity, is required.

Other specifications that may be important when selecting LEDs include lens type, viewing angle, and features such as duality and bipolarity. Lens types shapes can change the way emitted light is projected, and typically are either flat or domed. Viewing angle is dependent upon diffusion from the lens. Usually the larger the viewing angle, the less bright the LED. Diffused types generally have larger viewing angles and non-diffused types have smaller viewing angles. Dual devices include LEDs with two diode lamps in the same housing. Bipolar featured LEDs are those that, unlike most LEDs, can operate even if the voltage is reversed. Some models offer different color outputs when the voltage is reversed.

Light Emitting Diodes (LED) FAQs

What are the key advantages of using LEDs over traditional light sources in engineering applications?

Energy Efficiency: LEDs are more energy-efficient than traditional incandescent and fluorescent bulbs. They convert a higher percentage of electricity into light (90% is typical for an LED, with incandescent around 10%), resulting in less energy wasted as heat.

Longevity: LEDs have a significantly longer lifespan compared to traditional light sources. They can last approximately 40,000 hours, which is much longer than the 1,500 hours for incandescent bulbs and 12,000 hours for fluorescent bulbs.

Safety: LEDs emit significantly less heat than traditional lamps, reducing the risk of burns and fire hazards. Additionally, unlike fluorescent lamps, LEDs do not contain mercury, making them safer for the environment.

Versatility and Design Flexibility: LEDs are available in various forms, including flexible strips, which allow for innovative lighting designs and applications. They can be easily integrated into spaces with design constraints due to their small footprint.

Dimming and Control: LEDs can be easily dimmed and controlled, offering instant start and the ability to adjust brightness levels. This makes them suitable for advanced lighting control systems.

Low Maintenance: LEDs require less maintenance due to their durability and long service life, making them ideal for remote or hard-to-reach locations.

Environmental Impact: LEDs have a minimal environmental footprint due to their efficiency and lack of hazardous materials like mercury.

Color Rendering and Programmability: LEDs offer excellent color-rendering abilities and can be programmed for various lighting effects, making them suitable for applications requiring precise lighting control.

These advantages make LEDs a preferred choice in many engineering applications, from residential and commercial lighting to specialized industrial uses.

What are some of the environmental benefits of LEDs?

Energy Efficiency: LEDs are highly energy-efficient, converting a greater percentage of electricity into light compared to traditional incandescent and fluorescent bulbs. This efficiency reduces the overall energy consumption, leading to lower greenhouse gas emissions from power plants.

Reduced Heat Emission: LEDs emit significantly less heat than traditional light sources. This not only improves safety but also reduces the energy required for cooling systems in environments where lighting contributes to heat buildup.

Long Lifespan: The extended lifespan of LEDs, approximately 40,000 hours, means fewer replacements and less waste. This longevity reduces the environmental impact associated with manufacturing, transporting, and disposing of lighting products.

No Hazardous Materials: Unlike fluorescent lamps, LEDs do not contain mercury or other hazardous materials, making them safer for the environment and easier to dispose of at the end of their life cycle.

Minimal Environmental Footprint: LEDs have a minimal environmental footprint due to their efficiency and lack of hazardous materials. This makes them a more sustainable choice for various applications.

What are the safety benefits of using LEDs?

Here are the safety benefits of using LEDs:

Reduced Heat Emission: LEDs emit significantly less heat compared to traditional light sources. In traditional lamps, about 90% of the energy is emitted as heat, whereas LEDs convert most of their energy into light, minimizing heat production. This reduces the risk of burns and fire hazards.

No Hazardous Materials: Unlike fluorescent lamps, LEDs do not contain mercury or other hazardous materials. This makes them safer for both users and the environment, as there is no risk of mercury exposure or contamination during disposal.

Durability and Shock Resistance: LEDs are resistant to shock and vibrations, making them more durable and less prone to damage compared to other light sources. This enhances safety in environments where lighting fixtures might be subject to physical impacts.

Flame Retardancy and Low Outgassing: LEDs may be chosen for their flame retardancy and low outgassing properties, which are important safety features in certain applications, such as in environments with flammable gases or vapors.

These safety benefits make LEDs a reliable and secure choice for various engineering applications.

What are the design advantages of using LEDs in engineering applications?

Form Factor and Flexibility: LEDs are available in flexible strips, which allow for innovative and neat lighting solutions, such as cove lighting. They can be bent around corners, unlike traditional fluorescent tubes, providing greater design flexibility.

Small Footprint: LEDs often have a small footprint, with some as little as 1 mm². This makes them an attractive option for designers dealing with space constraints, enabling the integration of lighting in compact or intricate designs.

Dimming and Control Capabilities: LEDs can be easily dimmed and controlled, offering instant start and the ability to adjust brightness levels. This makes them suitable for advanced lighting control systems and allows for energy savings by dimming or switching off lights in unused areas.

Color Rendering and Programmability: Although not quite as consistent as incandescent lights, LEDs still offer excellent color-rendering abilities and can be programmed for various lighting effects. This makes them ideal for applications requiring precise lighting control and for creating visually appealing environments.

Improved Light Quality and Aesthetics: Advances in LED technology have improved light quality and design aesthetics, making them suitable for both functional and decorative lighting applications.

These design advantages make LEDs a versatile and attractive choice for a wide range of engineering applications, from architectural lighting to specialized industrial uses.

Can LEDs be used in hazardous locations and other difficult areas?

Industrial Settings: LEDs are used in industrial environments where hazardous conditions such as flammable gases and vapors are present. They are suitable for areas defined by NEC Class I, Division 2 and IEC Zone 2, which require lighting solutions that can operate safely under these conditions.

Public Areas: In public areas like parking garages, LEDs provide reliable lighting solutions. Their ruggedness and long lifespan make them ideal for locations that require low maintenance and can withstand severe weather conditions, excessive moisture, dust, and corrosive atmospheres.

Difficult Locations: LEDs are often the best choice for areas with low clearance and high ambient temperatures. Their ability to function in extreme conditions makes them suitable for challenging environments where other lighting solutions might fail.

Low Maintenance Requirements: The low maintenance nature of LEDs, combined with their durability, makes them a practical choice for hazardous locations as well as other areas where frequent maintenance is not feasible.

These applications highlight the versatility and safety benefits of LEDs in hazardous environments, making them a preferred choice for engineers and technical professionals working in such settings.