LED Diodes

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The LED diode is a type of semiconductor diode that is used to generate light from an electrical signal. LED displays group several LEDs in the same component to form numbers or letters

Introduction to LED Diodes

LED diodes, short for Light Emitting Diode, are semiconductor devices that convert electrical energy directly into visible light through the phenomenon of electroluminescence. LEDs are a widely used technology today due to their energy efficiency, durability and versatility in a variety of applications.

1. History and Development of LED Diodes

The concept of electroluminescence, the phenomenon behind the emission of light in LED diodes, was discovered in 1907 by H.J. Round, a British engineer. However, it was not until the 1960s that the first practical and efficient LED diodes were developed. In 1962, Nick Holonyak Jr., a General Electric engineer, created the first visible red-light LED using phosphorescent gallium arsenide. This breakthrough marked the beginning of the modern era of LEDs.

Over the following decades, significant advances were made in LED technology, including the expansion of wavelengths to encompass additional colors, such as green, yellow, and blue. One of the most important milestones occurred in 1994, when Shuji Nakamura developed the first high-efficiency blue LED using gallium nitride. This innovation enabled the creation of white LEDs by combining blue light with yellow phosphorus, opening the door to a wide range of LED lighting applications.

2. Operation and Structure of LED Diodes

LED diodes are mainly composed of semiconductor materials. The basic structure of an LED consists of a layer of active semiconductor material, which can be doped to adjust its electrical and optical properties. This active semiconductor is surrounded by layers of P- and N-type semiconductor materials, forming a PN junction.

When an electrical voltage is applied across the PN junction, electrons in the N region and holes in the P region recombine in the active region, releasing energy in the form of photons. The wavelength of the emitted light is determined by the energy gap of the semiconductor material, allowing the production of a variety of light colors.

3. Characteristics of LED Diodes

LED diodes have a number of distinctive characteristics that make them highly desirable compared to other lighting sources, such as incandescent or fluorescent lamps:

Energy efficiency: LEDs convert most of the electrical energy into light, minimizing heat losses. This makes them considerably more efficient than traditional lighting technologies.
Durability: LED diodes have a significantly longer lifespan than other light sources. They can last tens of thousands of hours of operation without replacement, reducing maintenance costs and waste generation.
Quick on and off: LEDs turn on instantly and require no warm-up time, unlike fluorescent lamps. This makes them ideal for applications where quick response is crucial, such as in signage or security lighting or even for the manufacturing of displays and video screens.
Dimming Control: LED diodes can be easily dimmed to adjust light intensity, making them versatile for a variety of lighting and design applications.
Shock and vibration resistance: Due to their solid construction and lack of brittle filaments, LEDs are more resistant to impact and vibration, making them suitable for applications in harsh environments.

4. Applications of LED Diodes

LED diodes are used in a wide variety of applications, ranging from general lighting to specialized applications:

Domestic and commercial lighting: LEDs are increasingly used in lamps and luminaires for indoor and outdoor lighting due to their energy efficiency and long life.
Automotive lighting: LEDs are used in vehicle headlights, taillights, brake lights and interior lights due to their low power consumption and quick response.
LED Displays and Panels: LEDs are used in display screens, information panels, and digital signage due to their brightness, contrast, and individual pixel controllability.
Consumer electronics: LEDs are found in electronic devices such as televisions, monitors, smartphones, watches, and home appliances, providing status indicators and backlighting.
Signaling and security lighting: LEDs are used in traffic signs, traffic lights, emergency exit signs and security lighting systems due to their reliability and visibility.
Decorative and architectural lighting: LEDs are used in decorative lighting applications, highlighting architectural features and creating ambient lighting effects.

5. Future Challenges and Advances

Although LED diodes have advanced significantly since their initial invention, they still face challenges and opportunities for future improvements:

Improved energy efficiency: Researchers continue to work to increase the efficiency of LEDs, further reducing their energy consumption and increasing their light output.
Development of new wavelengths and colors: New semiconductor materials are being investigated to expand the range of colors available in LEDs and explore applications in areas such as agriculture and medicine.
Thermal management improvements: Heat management is a crucial aspect for the reliability and lifespan of LEDs. New materials and packaging designs are being developed to improve thermal dissipation and reduce stress on LED devices.
Integration with smart systems: LEDs are increasingly integrating with smart control systems and lighting networks to provide adaptive and efficient lighting based on environmental conditions and user preferences.

In summary, LED diodes have revolutionized the lighting industry and continue to be an ever-evolving technology with vast potential in a variety of applications. With their energy efficiency, durability and versatility, LEDs will continue to play a vital role in lighting and technology in the future.

How does an LED diode work?

Electronic Operation

The operation of an LED is based on the principle of electroluminescence, a phenomenon in which electrons in a semiconductor material recombine with holes, releasing energy in the form of photons of light. This process occurs within the active region of the LED diode when an electrical voltage is applied across the PN junction.

PN Junction Structure: A typical LED consists of a PN junction formed by the union of two semiconductors, one P-type and one N-type. In the junction region, the electrons of the N-type material and the holes of the P-type material meet. spread to the other side. When a forward voltage is applied (positive on the P side and negative on the N side), a current flow is created through the PN junction.
Electron-Hole Recombination: Electrons from the N region and holes from the P region recombine in the active region of the LED when current flows through the PN junction. During this recombination process, electrons release energy in the form of photons of light. The wavelength of the emitted light is determined by the energy gap of the semiconductor material.

Semiconductor Materials

The semiconductor materials used in LED diodes play a crucial role in their operation and determine their optical and electrical properties. The most common materials are gallium arsenide (GaAs), gallium phosphide (GaP), gallium nitride (GaN), and indium gallium nitride (InGaN). The choice of material determines the wavelength of the light emitted and therefore the color of the LED.

Energy Gap: The energy gap of the semiconductor material is the minimum energy required for an electron to jump from the valence band to the conduction band. This energy gap determines the energy and wavelength of the light emitted by the LED. Materials with larger energy gaps emit light in shorter wavelengths and bluer colors, while materials with smaller energy gaps emit light in longer wavelengths and redder colors.

Physical Construction

LED diodes are built in different shapes and sizes to suit a variety of applications. The physical construction of a typical LED includes:

Semiconductor Chip: The semiconductor chip, where light emission occurs, is mounted on a substrate of semiconductor material. This chip can be rectangular, circular or another shape, depending on the design of the LED.
Encapsulation: The semiconductor chip is encapsulated in a transparent epoxy resin or glass lens to protect it and concentrate the emitted light in the desired direction. Encapsulation also provides electrical insulation and protection against environmental agents such as moisture and dust.
Electrical Connections: The semiconductor chip is connected to metal electrodes that allow electrical connection with an external circuit. These electrodes can be arranged on the top, side or bottom of the package, depending on the LED type and design layout.

Light Intensity Control

The luminous intensity of an LED can be controlled by varying the electrical current that flows through it. Although LED diodes are inherently non-linear devices, their brightness can be adjusted using pulse width modulation (PWM) techniques or by directly varying the supply current. This allows the brightness of the LED to be adjusted to suit the specific lighting needs in different applications.

Efficiency and Thermal Management Considerations

Efficiency and thermal management are important aspects in the operation of LED diodes. As current flows through the LED, heat is generated in the active region. Excess heat can reduce the efficiency of the LED and shorten its lifespan. Therefore, it is important to design effective heat dissipation systems, such as heat sinks and metal PCBs, to keep the LED temperature within safe ranges and optimize its performance and durability.

In conclusion, the operation of an LED is based on the principle of electroluminescence, where the recombination of electrons and holes in an active semiconductor material generates light. Material choice, physical construction, and control of luminous intensity are key aspects in the design and efficient operation of LED diodes in a variety of lighting and electronics applications.

Types of LED diodes

LED diodes are extremely versatile electronic components that are used in a wide range of applications. In addition to individual LEDs, there are various types of LED diodes and display configurations used in electronics and lighting applications. Here are some of the most common types:

Single color LEDs (visible spectrum)
These are the most basic and common LEDs. They emit light in a single color and are widely used in signage, lighting and display applications. They come in a variety of colors, including red, green, blue, yellow, white, among others. Single-color LEDs can be found in a variety of packages, such as surface-mount LED (SMD), through-hole LED, and high-power LED.

RGB LEDs (Red, Green, Blue)

These LEDs contain three different semiconductor chips that emit red, green and blue light. By mixing these three lights in different proportions, a wide range of colors can be created. RGB LEDs are essential in lighting variable colors and creating dynamic light effects.

Bicolor and Tricolor LEDs
They are LEDs that contain two or three semiconductor chips, which allows them to emit two or three different colors. Bi-color LEDs can change between two colors, such as red and green, while tri-color LEDs can display three colors, such as red, green, and yellow.

Ultraviolet and Infrared LEDs

Ultraviolet (UV) LEDs emit light in the ultraviolet region of the electromagnetic spectrum and are used in applications such as resin curing, disinfection, fluorescence detection, and counterfeit detection. Infrared (IR) LEDs emit light in the infrared region and are used in remote control, security, night vision, and proximity sensor applications.

LED displays:

In addition to individual LEDs, there are LED displays that consist of multiple LED diodes arranged in an array to form characters, numbers, or other symbols. One of the most common types of LED displays is the 7-segment display. This type of display consists of seven individual segments arranged in an "8" shape and is commonly used to display numerical digits. Each segment can be turned on or off individually to represent numbers 0 to 9 and some letters, such as A, B, C, etc. 7-segment displays are widely used in applications such as digital clocks, thermometers, stopwatches, and control panels.

COB LEDs (Chip-on-Board)

COB LEDs are an advanced technology that consists of multiple LED chips mounted directly on a substrate or printed circuit board (PCB).
The arrangement of the LED chips on the same surface allows for greater power density and better light distribution.
COB LEDs provide higher luminosity and efficiency compared to individual LEDs, making them ideal for high power, high luminosity applications such as large area lighting, outdoor lighting, floodlights, spotlights and flood lamps. I know about a heat sink.

High Brightness LED (HBLED)

They are similar to COBs. High Brightness LEDs (HBLED) are LED diodes designed to produce very intense light output.
These LEDs typically incorporate an array of high-power LED chips mounted on a metal substrate for better heat dissipation.
HBLEDs are used in applications that require high intensity lighting, such as stage lighting, studio lighting, automotive lighting, facade lighting and floodlights.

LED Matrix Displays

These displays consist of a matrix of LED diodes arranged in rows and columns. Each individual LED on the matrix can be turned on or off to represent specific alphanumeric characters, graphics, or patterns. LED matrix displays are highly flexible and are used in a variety of applications, including advertising signs, information systems, and electronic games.

Laser LEDs:

Laser LEDs, also known as laser diodes, are a specialized variant of LED diodes that emit highly addressable, coherent light instead of scattered light. Although they share some similarities with conventional LEDs, such as the basic PN junction structure and carrier recombination-based operation, laser LEDs have distinctive characteristics that make them unique. Here is a more detailed description of laser LEDs:

1. Principle of Operation
The operation of a laser LED is based on the same basic principle as that of a conventional LED: the recombination of carriers in a semiconductor active region. However, unlike standard LEDs, laser LEDs use a process called "stimulated emission of radiation" to generate coherent, highly directional light.

In a laser LED, the semiconductor active region is confined between two highly reflective mirrors, one of which is partially transparent to allow laser light to escape. When an electrical current is applied through the laser diode, electrons and holes recombine in the active region, generating photons that travel back and forth between the reflecting mirrors. This stimulated emission process amplifies the light and produces a coherent, high-intensity beam that emerges through the partially transparent mirror.

2. Structure and Materials
Laser LEDs are built with specific semiconductor materials, such as gallium arsenide (GaAs) and indium gallium arsenide (InGaAs). The basic structure of a laser LED includes:

Semiconductor Active Region: This is the region where carrier recombination and laser light emission occurs. It usually consists of several thin layers of semiconductor materials doped with different impurities to tune the optical and electrical properties.

Reflective Mirrors: Reflective mirrors, one at each end of the active region, form a resonant cavity that amplifies laser light through multiple reflection. These mirrors are typically made from alternating layers of materials with different refractive indices to maximize reflection.

Gain Zone: This is the region where optical amplification occurs through the process of stimulated emission of radiation. The length and composition of this region determine the spectral and emission properties of the laser LED.

3. Features and Applications
Laser LEDs have several distinctive characteristics that make them suitable for specific applications:

Coherence: The light emitted by a laser LED is coherent, meaning that all light waves have the same phase and direction. This allows laser LEDs to produce narrow, highly directional beams that are useful in signaling, optical communications, and medical applications.

Monochromaticity: Laser LEDs emit light in a single wavelength or color, making them suitable for applications requiring spectral precision, such as barcode reading, laser printing, and spectroscopy.

High Luminous Intensity: Laser LEDs can generate extremely bright and concentrated light beams, making them ideal for lighting, projection and cutting applications.

Low Divergence: Laser LED light beams have low divergence, meaning they maintain their size and shape over long distances. This makes them useful in applications such as telemetry, tracking and positioning.

4. Applications of LED Lasers
Laser LEDs are used in a wide variety of applications, including:

Optical Communications: Laser LEDs are essential in optical communications systems, such as fiber optics and laser transmission, where they are used to send data over long distances with high speed and precision.

Medicine and Therapy: In medicine, laser LEDs are used in light therapies to treat a variety of medical conditions, such as stimulating cell growth, reducing pain, and promoting wound healing.

Scientific Instrumentation: Laser LEDs are used in scientific instruments, such as fluorescence microscopes, spectrometers, and optical trap lasers, to perform precise measurements and research experiments.

Industry and Manufacturing: In industry, laser LEDs are used in cutting, welding, marking and engraving applications, where they provide a highly controlled and powerful light source for high-precision manufacturing processes.

In summary, LED diodes are available in a variety of types and configurations to suit a wide range of applications. From simple individual LEDs to complex matrix displays, LEDs are essential components in modern electronics and lighting.

Sizes and/or capsules used in LED diodes

Without being an exhaustive list, it shows you the most commonly used capsules, as well as their common characteristics in a very general way, especially what refers to power, current and viewing angle.

For through-hole or conventional LED diodes:

1. 3mm LED (T-1):

They are the most common and are used in a wide variety of applications.
Diameter: 3mm
Height: 2.5mm
Viewing angle: 20-30 degrees
Current: 20mA
Power: 5-10mW

2. 5mm LED (T-1 3/4):

They are brighter than 3mm LEDs and are used in applications requiring higher light output.
Diameter: 5mm
Height: 4.8mm
Viewing angle: 20-30 degrees
Current: 20mA
Power: 10-20mW

3. 8mm LED:

They are the brightest of the conventionally mounted LEDs and are used in applications requiring maximum light output.
Diameter: 8mm
Height: 5.6mm
Viewing angle: 20-30 degrees
Current: 20mA
Power: 20-30mW

4. 10mm LED:

They are less common than 3mm, 5mm and 8mm LEDs, but are used in some special applications.
Diameter: 10mm
Height: 7.5mm
Viewing angle: 20-30 degrees
Current: 20mA
Power: 30-40mW

5. LED Piranha or superflux:

They are high-power LEDs that are characterized by their square shape.
Diameter: 5mm
Height: 4.6mm
Viewing angle: 120 degrees
Current: 350mA
Power: 100-150mW

6. LED PLCC:

They are high-power LEDs that are characterized by their plastic encapsulation.
Diameter: 5mm
Height: 4.8mm
Viewing angle: 120 degrees
Current: 350mA
Power: 100-150mW

Capsule sizes for LED diodes in SMD mounting:

1. LED 0402:

They are the smallest of the SMD LEDs and are used in applications that require a very small size.
Dimensions: 0.4mm x 0.2mm
Viewing angle: 120 degrees
Current: 20mA
Power: 5-10mW

2. LED 0603:

They are slightly larger than 0402 LEDs and are used in a wide variety of applications.
Dimensions: 0.6mm x 0.3mm
Viewing angle: 120 degrees
Current: 20mA
Power: 5-10mW

3. LED 0805:

They are a popular size for SMD LEDs and are used in applications that require a good balance between size and power.
Dimensions: 0.8mm x 0.5mm
Viewing angle: 120 degrees
Current: 20mA
Power: 10-20mW

4. LED 1206:

They are a popular size for SMD LEDs and are used in applications requiring higher light output.
Dimensions: 1.2mm x 0.6mm
Viewing angle: 120 degrees
Current: 20mA
Power: 20-30mW

5. LED 3528:

They are high-power SMD LEDs that are characterized by their large size.
Dimensions: 3.5mm x 2.8mm
Viewing angle: 120 degrees
Current: 150mA
Power: 50-100mW

6. 5050 LED:

They are high-power SMD LEDs that are characterized by their even larger size.
Dimensions: 5.0mm x 5.0mm
Viewing angle: 120 degrees
Current: 150mA
Power: 100-150mW

LED capsule finishes (tinted, transparent, diffused)

The different tinted, clear and diffused finishes are encapsulation options for LED diodes that affect the dispersion and intensity of the emitted light. Each has specific characteristics that make them suitable for different applications. Here is an explanation of each:

Tinted finish (tinted LED):

Features: Tinted finish refers to a colored coating applied to the LED diode encapsulation.
This coating provides a specific color or tone to the light emitted by the LED.
The color of the coating can vary from transparent to dark, depending on the degree of tinting.
The color of the light emitted by the LED will be influenced by the color of the tinted coating.
Applications: LEDs with a tinted finish are commonly used in applications where lighting with a specific hue or a particular aesthetic appearance is required.
They are used in decorative lighting, ambient lighting, signage and specialized lighting effects.

Clear finish (clear LED):

Features: The clear finish refers to a transparent encapsulation that allows the light emitted by the LED diode to spread with little or no obstruction. This type of encapsulation provides direct and clear light output, without significant diffraction. The light emitted by a clear finish LED tends to be brighter and more concentrated compared to other finishes.

Applications: Clear finish LEDs are ideal for applications where bright, focused light output is needed, such as indicators, signage, panel lighting and backlighting.

Diffused finish (diffused LED):

Features: The diffused finish refers to a package that has been treated to disperse the light emitted by the LED diode more uniformly. This treatment reduces the intensity of direct light and softens the edges of the shadow, creating a softer, more diffuse light output. The diffused finish also helps reduce glare and provides more uniform light distribution.

Applications:

LEDs with a diffused finish are suitable for applications where soft, uniform lighting is needed, such as ambient lighting, indoor signage lighting, backlighting of displays and instrument panels.

Summary:
The tinted finish provides a specific color to the emitted light and is used in aesthetic or design applications.
The clear finish provides bright, direct light output, ideal for applications where high, focused light intensity is required.
The diffused finish disperses light more evenly and softly, suitable for applications requiring soft, glare-free lighting. The choice between these finishes will depend on the specific needs of the application, including the desired aesthetics, the required luminous intensity and the type of light dispersion desired

Graph of the viewing angle of a 2θ½ LED diode

The graph that represents the viewing angle or opening of an LED diode is usually represented in polar coordinates. The polar graph of the luminosity of an LED diode is a graphical representation of the intensity of the light emitted by the LED as a function of the emission angle. It is a circular graph in which the radial axis represents the light intensity and the angle θ represents the emission angle with respect to the axis perpendicular to the surface of the LED.

Explanation of θ:

θ = 0°: Corresponds to the direction perpendicular to the surface of the LED. In this case, the light intensity is maximum.
θ > 0°: As θ increases, the light intensity decreases.
θ = 90°: The light intensity is minimum.
θ > 90°: The light intensity increases again, but does not reach the same intensity as at θ = 0°.

Graph shape:

The shape of the luminosity polar graph depends on the type of LED. LEDs with a wide viewing angle have a wider graphic, while LEDs with a narrow viewing angle have a more pointed graphic.

We define the angle θ/2, the one in which the light intensity is just half the maximum intensity, that is, half of that at 0º. Taking into account that the LED diode is symmetrical, the opening angle of the LED is double and is expressed as 2θ½. In the following example we will see it more clearly:

The cut-off points of the intensity value equal to 0.5 with the lobe of the graph are at 15º and -15º. Therefore we define that the LED diode in the graph has an opening of 30º or 2θ½= 30º

Graph of the spectrum of an LED diode

The luminous frequency graph of an LED shows the amount of light emitted by the LED as a function of the wavelength of that light, also known as the LED emission spectrum. To understand this graph, it is useful to understand some basic concepts:

Emission Spectrum:

The emission spectrum of an LED represents the distribution of the light intensity emitted by the LED at different wavelengths of the electromagnetic spectrum.
Each LED emits light at a specific wavelength or a narrow range of wavelengths, depending on the semiconductor materials used in its construction.

Wavelength:

Wavelength is the distance between two adjacent crests of a light wave. It is measured in nanometers (nm).
In the visible spectrum, the shorter wavelengths correspond to the colors blue and violet, while the longer wavelengths correspond to the colors red and orange.

Light Frequency:

The luminous frequency is the amount of light emitted by the LED at a certain wavelength. It is expressed in units such as watt per square meter per nanometer (W/m²/nm) or similar.

The light frequency graph shows how the light intensity of the LED varies depending on the wavelength.

Graph Interpretation:

On the graph, the horizontal axis represents the wavelength in nanometers (nm), while the vertical axis represents the light intensity in units such as W/m²/nm or similar.
The curve on the graph shows how the luminous intensity of the LED varies depending on the wavelength. This curve may be continuous or may show peaks and valleys depending on the specific characteristics of the LED and the materials used in its manufacture.
The peaks on the graph represent the wavelengths at which the LED emits the most light, while the valleys represent the wavelengths at which it emits less light or no light.
The shape and width of the curve on the graph depend on several factors, including the semiconductor material used in the LED, the package design, and any optical coatings applied to the LED.

In the following graph example we see how the maximum intensity occurs at a frequency whose wavelength is approximately 455nm. and we have a valley zone between 480nm and 520nm. λ = 455nm.

color spectrum of an LED diode

Applications:

The luminous frequency graph is useful for LED lighting designers and manufacturers to understand the spectral characteristics of LEDs and select the right ones for their specific applications.
It is also important for researchers and scientists studying semiconductor materials and optical properties of LEDs to improve their efficiency and performance.
In summary, the luminous frequency graph of an LED provides information on how the luminous intensity of the LED varies at different wavelengths of the electromagnetic spectrum, which is crucial for understanding and optimizing its performance in various lighting applications.

Chromaticityr of an LED diode

The chromaticity of an LED diode refers to the color quality of the light it emits. The color scheme can be represented by the coordinates:

x: Indicate the position of the color in the red-green eje
y: Indicates the position of the color on the azul-amarillo eje

The color of an LED is only represented by the manufacturer's data and is very important among others to ensure that all LEDs have a mismatched color in an application.

The color of an LED may vary with temperature, direction and voltage.
The color of an LED can be measured using an spectrometer.
There are different color spaces to define color, such as the CIE 1931 color space, the CIE 1976 color space and the sRGB color space.

Color reproduction index or CRI

The CRI, or color reproduction index, of an LED diode is a measure of the capacity of the LED to reproduce the colors of a precise format in comparison with a natural light source. Expressed in a scale from 0 to 100, if 100 is the best possible color reproduction.

Explanation:

High CRI value (90-100): Colors are reproduced with high precision and are natural. Ideal for applications where color accuracy is crucial, such as museums, clothing stores, etc.
Average CRI value (80-90): Color reproduction is good, but some colors may be slightly faded. Suitable for the majority of general applications.
Low CRI value (0-80): Color reproduction is deficient and colors may be distorted. Only this is recommended for applications where color accuracy is not important.

Factors that affect the CRI:

Type of LED: High power LEDs only have a higher CRI than low power LEDs.
LED Color: Warm white LEDs may have a higher CRI than cold white LEDs.
LED Manufacturer: Different manufacturers may have different manufacturing processes that affect the CRI.
Importance of CRI:

The CRI is important for:

Select the appropriate LED for a specific application: In applications where color accuracy is crucial, like museums or clothing stores, a high CRI is required.
Ensure that the colors are natural: A CRI alto ayuda ensures that the colors are as realistic as possible.
Avoid color distortion: A low CRI may cause colors to become distorted or distorted.

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