The LED bulb is a type of semiconductor diode that can convert electrical energy into light energy; it is often abbreviated as LED. The light-emitting diode, abbreviated as LED, is a commonly used light-emitting device that emits light by the recombination of electrons and holes to release energy. It is widely used in the field of lighting. The light-emitting diode can efficiently convert electrical energy into light energy and has a wide range of uses in modern society, such as lighting, flat panel displays, medical devices, etc.
Working Principle of LED Diode
Like an ordinary diode, a light-emitting diode is composed of a PN junction and also has unidirectional conductivity. When a forward voltage is applied to a light-emitting diode, the holes injected from the P region to the N region and the electrons injected from the N region to the P region recombine with the electrons in the N region and the holes in the P region respectively within several micrometers near the PN junction, producing spontaneous radiation fluorescence. The energy states of electrons and holes in different semiconductor materials are different. When electrons and holes recombine, different amounts of energy are released. The more energy is released, the shorter the wavelength of the emitted light. Commonly used are diodes that emit red, green, or yellow light. The reverse breakdown voltage of a light-emitting diode is greater than 5 volts. Its forward volt-ampere characteristic curve is very steep. When in use, a current-limiting resistor must be connected in series to control the current passing through the diode.

LED Series Resistor Circuit
The core part of a light-emitting diode is a wafer composed of a P-type semiconductor and an N-type semiconductor. There is a transition layer between the P-type semiconductor and the N-type semiconductor, called a PN junction. In the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, excess energy is released in the form of light, thus directly converting electrical energy into light energy. When a reverse voltage is applied to the PN junction, it is difficult for minority carriers to be injected, so it does not emit light. When it is in the forward working state (that is, a forward voltage is applied at both ends), when the current flows from the anode to the cathode of the LED, the semiconductor crystal emits light of different colors from ultraviolet to infrared. The intensity of the light is related to the current.
Classification of LED Diode
Light-emitting diodes can also be divided into ordinary single-color light-emitting diodes, high-brightness light-emitting diodes, ultra-high-brightness light-emitting diodes, color-changing light emitting diodes, flashing light emitting diodes, voltage-controlled light emitting diodes, infrared light emitting diodes, and negative resistance light emitting diodes.
Ordinary Single-Color Light Emitting Diode
Ordinary single-color light-emitting diodes have the advantages of small volume, low operating voltage, low operating current, uniform and stable luminescence, fast response speed, and long service life. They can be driven and lit by various DC, AC, and pulse power sources. It belongs to a current-controlled semiconductor device. When in use, a suitable current-limiting resistor must be connected in series. The luminescence color of an ordinary single-color light-emitting diode is related to the wavelength of luminescence, and the wavelength of luminescence depends on the semiconductor material used to manufacture the light-emitting diode. The wavelength of a red light-emitting diode is generally 650-700nm, the wavelength of an amber light-emitting diode is generally 630-650nm, the wavelength of an orange light-emitting diode is generally about 610-630nm, the wavelength of the yellow light-emitting diode is generally about 585nm, and the wavelength of a green light emitting diode is generally 555-570nm.

(Ultra) High-Brightness Single-Color Light Emitting Diode (2 types)
The semiconductor materials used by high-brightness single-color light-emitting diodes and ultra-high-brightness single-color light-emitting diodes are different from those of ordinary single-color light-emitting diodes, so the luminous intensity is also different. Generally, high-brightness single-color light-emitting diodes use materials such as gallium aluminum arsenide (GaAlAs), ultra-high-brightness single-color light-emitting diodes use materials such as gallium indium arsenide phosphide (GaAsInP), and ordinary single-color light emitting diodes use materials such as gallium phosphide (GaP) or gallium arsenide phosphide (GaAsP).
Color-Changing Light Emitting Diode
The color-changing light-emitting diode is a light-emitting diode that can change its luminescence color.
The luminescence color types of color-changing light-emitting diodes can be divided into two-color light-emitting diodes, three-color light-emitting diodes, and multi-color (with four colors of red, blue, green, and white) light-emitting diodes.
Color-changing light-emitting diodes can be divided into two-terminal color-changing light-emitting diodes, three-terminal color-changing light-emitting diodes, four-terminal color-changing light-emitting diodes, and six-terminal color-changing light emitting diodes according to the number of pins.
Flashing Light Emitting Diode
The flashing light-emitting diode (BTS) is a special light-emitting device composed of a CMOS integrated circuit and a light-emitting diode. It can be used for alarm indication and under-voltage and over-voltage indication. When in use, the flashing light-emitting diode does not need to be connected with other components externally. As long as an appropriate DC operating voltage (5V) is applied across its pins, it can flash and emit light.
Voltage-Controlled Light Emitting Diode
Ordinary light-emitting diodes belong to current-controlled devices. When in use, a current-limiting resistor with an appropriate resistance value must be connected in series. The voltage-controlled light-emitting diode (BTV) integrates a light-emitting diode and a current-limiting resistor into one body. When in use, it can be directly connected in parallel across the power supply.
Infrared Light Emitting Diode
The infrared light emitting diode, also known as the infrared emitting diode, is a light-emitting device that can directly convert electrical energy into infrared light (invisible light) and radiate it. It is mainly used in various light control and remote control transmitting circuits. The structure and principle of the infrared light-emitting diode are similar to those of ordinary light-emitting diodes, only the semiconductor materials used are different. Infrared light-emitting diodes usually use materials such as gallium arsenide (GaAs) and gallium aluminum arsenide (GaAlAs) and are encapsulated in fully transparent or light blue or black resin. Commonly used infrared light-emitting diodes include SIR series, SIM series, PLT series, GL series, HIR series, and HG series.
Typical LED Characteristics
Semiconductor Material
|
Wavelength
|
Color
|
VF @20mA
|
GaAs
|
850-940nm
|
Infra-Red
|
1.2v
|
GaAsP
|
630-660nm
|
Red
|
1.8v
|
GaAsP
|
605-620nm
|
Amber
|
2.0v
|
GaAsP:N
|
585-595nm
|
Yellow
|
2.2v
|
AlGaP
|
550-570nm
|
Green
|
3.5v
|
SiC
|
430-505nm
|
Blue
|
3.6v
|
GaInN
|
450nm
|
White
|
4.0v
|
Relevant Parameters of LED Diode
Several important aspects of the optical parameters of LEDs are luminous flux, luminous efficiency, luminous intensity, light intensity distribution, and wavelength.
Luminous efficiency and luminous flux. Luminous efficiency is the ratio of luminous flux to electrical power, and the unit is generally lm/W. Luminous efficiency represents the energy-saving characteristics of a light source and is an important indicator for measuring the performance of modern light sources. Luminous intensity and light intensity distribution. The luminous intensity of an LED characterizes its luminous intensity in a certain direction. Since the light intensity of an LED varies greatly in different spatial angles.
The light intensity distribution characteristic of an LED. This parameter has great practical significance and directly affects the minimum viewing angle of an LED display device. For example, for large LED color displays in stadiums, if the single-tube distribution range of the selected LED is very narrow, then viewers at a large angle facing the display screen will see distorted images. Moreover, traffic sign lights also require a large range of people to be able to recognize them.
For the spectral characteristics of LEDs, we mainly look at whether their monochromaticity is excellent and pay attention to whether the main colors such as red, yellow, blue, green, and white LEDs are pure. Because in many occasions, such as traffic signals, the color requirements are relatively strict.

Characteristics and Advantages of Light-Emitting Diodes
Efficient: The energy conversion efficiency of light-emitting diodes is high and can reach more than 50%.
Energy-saving: The power consumption of light-emitting diodes is low, only 1/10 to 1/5 of that of incandescent lamps and fluorescent lamps.
Environmentally friendly: Light-emitting diodes do not contain harmful substances such as mercury and are friendly to the environment.
Long lifespan: The lifespan of light-emitting diodes can generally reach more than 100,000 hours.
High reliability: Light-emitting diodes have stable voltage and current and are not easily affected by the external environment.
Cleaner: It does not refer to the cleanliness of the lamp surface and inside. Instead, this lamp belongs to a cold light source that does not generate too much heat and will not attract insects that are photophilic and heat-loving. Especially in summer, there will be a particularly large number of insects in rural areas.
Applications of LEDs
LED Display Screen
Since the mid-1980s, single-color and multi-color display screens have come out, initially as text screens or animation screens. In the early 1990s, with the development of computer technology and integrated circuit technology, the video technology of LED display screens was realized, and television images were directly displayed on the screen. Especially in the mid-1990s, blue and green ultra-high-brightness LEDs were successfully developed and quickly put into production, greatly expanding the application of outdoor screens with an area ranging from 100 to 300 square meters.
LED display screens have been widely used in stadiums, squares, venues, and even streets and shopping malls. The NASDAQ full-color screen on Times Square in the United States is the most famous. The screen area is 120 feet × 90 feet, equivalent to 1005 square meters, and is made of 19 million ultra-high-bright blue, green, and red LEDs. In addition, applications in areas such as stock quotation screens, bank exchange rate screens, and interest rate screens also account for a large proportion. Recently, there has also been significant development in information screens on expressways and viaducts.
Traffic Signal Lights
LEDs have been used as light sources for navigation lights for many years, and the current work is to improve and perfect them. Road traffic signal lights have made great progress in recent years, with rapid technological development and rapid application development. In China, there are about 40,000 sets of orders each year. In California, the United States, within one year, 50,000 sets of traditional light source signal lights were replaced with LED traffic signal lights. According to the use effect, the effects of long lifespan, power saving, and maintenance-free are obvious. The peak emission wavelengths of LEDs used are 630nm for red, 590nm for yellow, and 505nm for green. The problem that should be noted is that the driving current should not be too large. Otherwise, the high-temperature conditions in summer sunlight will affect the lifespan of LEDs.
Recently, LED airport-specific signal lights used as beacons, floodlights, and omnidirectional lights at airports have also been successfully developed and put into use. The feedback from various parties is very good. It has independent intellectual property rights, has been granted two patents, has good reliability, saves electricity, is maintenance-free, and can be promoted and applied to various airports to replace the old signal lights that have been in use for decades. Not only is the brightness high, but also because the LED has good color purity, it is particularly distinct and easy to recognize signals.
Automotive Lights
Ultra-high-brightness LEDs can be made into brake lights, taillights, and turn signal lights for cars. They can also be used for instrument lighting and interior lighting. They have obvious advantages over incandescent lamps in terms of vibration resistance, power saving, and long lifespan. When used as brake lights, its response time is 60ns, much shorter than the 140ms of incandescent lamps. When driving on a typical expressway, it will increase the safety distance by 4-6 meters.
Backlight of LCD Screen
As the backlight of liquid crystal displays, LEDs can not only be green, red, blue, and white but also can be used as a color-changing backlight. Many products have entered the production and application stage. Recently, using LEDs to make backlights for liquid crystal displays on mobile phones has improved the product grade and has a very good effect. The backlight of a 15-inch (1 inch ≈ 2.5 centimeters) LCD screen made of 8 blue, 24 green, and 32 red Luxeon LEDs can reach 120W, 2500 lm, and a brightness of 18000 nits (nit, cd/m²). The backlight of a 22-inch LCD screen has also been made. It is only 6mm thick. Not only is the color mixing effect good, but the color rendering index also reaches more than 80. Although large backlights are still in the development stage, they have great potential.
Lighting Decorations
Due to the increase in brightness and the decrease in the price of light emitting diodes, coupled with a long lifespan, power saving, and easier driving and control compared to neon lights, and the ability to not only flash but also change colors, single-color, multi-color, and even color-changing light-emitting columns made of ultra-high-brightness LEDs combined with variously shaped colored light-emitting units can be used to decorate tall buildings, bridges, streets, squares, and other landscape projects with very good effects, presenting a scene of colorful, starry twinkling and flowing brilliance. Many units have produced LED light columns of more than 10,000 meters and tens of thousands of colored lights, which are being gradually promoted. It is estimated that it will gradually expand and form an independent industry.
Lighting Source
As a lighting source, the LED light source should be white light. As a white light LED lighting fixture for military use, some varieties have been put into mass production. Since the LED light source has no infrared radiation and is easy to conceal, coupled with its advantages of vibration resistance, suitability for battery power supply, solid structure, and portability, it will have greater development in special lighting sources. As civilian lawn lights and buried lights, they have been mass-produced. They are also used as microscope field illumination, flashlights, headlamps for surgeons, lighting for museums or art exhibitions, and reading lamps.
Greenhouse Supplemental Lighting
Light is one of the most important environmental factors for plant growth and development. It regulates plant growth and development, morphogenesis, photosynthesis, material metabolism, and gene expression. Therefore, greenhouse supplemental lighting is an important way to achieve high-quality and high-yield plants. In recent years, light-emitting diodes have been more and more widely used in plant factories. The advantages of LEDs such as narrow wavelength bands, low energy consumption, small volume, high efficiency, resistance to aging, and low heat consumption have made them a new light source used by many researchers on light quality. So far, there have been countless studies on the effects of light environment on the macroscopic morphology, yield, and quality of plants, as well as the effects on cell microstructure, plant differentiation, and secondary metabolites using LED light sources. More details: Comprehensive Diodes' Introduction