Light-emitting diodes can also be divided into ordinary monochromatic 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.
There are two control modes for LEDs: constant current and constant voltage. There are multiple dimming methods, such as analog dimming and PWM dimming. Most LEDs use constant current control, which can keep the LED current stable and not easily affected. The change of VF can extend the service life of LED lamps .
Monochrome LED
Ordinary monochromatic light-emitting diode
Ordinary monochromatic light-emitting diodes have the advantages of small size, low working voltage, low working current, uniform and stable light emission, fast response speed, and long life. They can be driven by various DC, AC , pulse and other power sources to light up. It is a current-controlled semiconductor device, and suitable current-limiting resistors need to be connected in series when used.
The light-emitting color of ordinary monochromatic light-emitting diodes is related to the light-emitting wavelength , and the light-emitting wavelength depends on the semiconductor material used to manufacture the light-emitting diode. The wavelength of red light-emitting diodes is generally 650-700nm, the wavelength of amber light-emitting diodes is generally 630-650nm, the wavelength of orange light-emitting diodes is generally about 610-630nm, the wavelength of yellow light-emitting diodes is generally about 585nm, and the wavelength of green light-emitting diodes Generally, it is 555~570nm.
High-brightness monochromatic light-emitting diode
The semiconductor materials used in high-brightness monochromatic light-emitting diodes and ultra-high-brightness monochromatic light-emitting diodes are different from ordinary monochromatic light-emitting diodes, so the intensity of light emission is also different. Generally, high-brightness monochromatic light-emitting diodes use gallium aluminum arsenide (GaAlAs) and other materials, ultra-high-brightness monochromatic light-emitting diodes use materials such as gallium indium arsenide (GaAsInP), and ordinary monochromatic light-emitting diodes use gallium phosphide (GaP). ) Or gallium arsenide phosphorous (GaAsP) and other materials.
Color-changing light-emitting diode
Color-changing light-emitting diodes are light-emitting diodes that can change the color of light. Color-changing light-emitting diodes can be divided into two-color light-emitting diodes, three-color light-emitting diodes and multi-color (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
Blinking light-emitting diode (BTS) is a special light-emitting device composed of CMOS integrated circuit and light-emitting diode, which can be used for alarm indication and under-voltage and over-voltage indication.
When the flashing light-emitting diode is in use, there is no need to connect other components, as long as the appropriate DC working voltage (5V) is added to the two ends of its pin, it can flash and emit light.
Infrared LED
Infrared light-emitting diodes are also called infrared emitting diodes. They are light-emitting devices that can directly convert electrical energy into infrared light (invisible light) and radiate out. They are mainly used in various light-controlled and remote-control transmitting circuits.
The structure and principle of infrared light-emitting diodes are similar to those of ordinary light-emitting diodes, but the semiconductor materials used are different. Infrared light-emitting diodes usually use gallium arsenide (GaAs), gallium aluminum arsenide (GaAlAs) and other materials, and are packaged in fully transparent or light blue, black resin.
Commonly used infrared light-emitting diodes include SIR series, SIM series, PLT series, GL series, HIR series and HG series.
UV LED
Ultraviolet light-emitting diodes (UV LEDs) based on semiconductor materials have the advantages of energy saving, environmental protection and long life, and have great application value in the fields of sterilization, medical treatment, and biochemical testing. In recent years, ultraviolet semiconductor optoelectronic materials and devices in the world attracted more and more attention, become hot topics. On December 9-12, 2018, the third "International Symposium on Ultraviolet Materials and Devices" (IWUMD-2018) hosted by the Institute of Semiconductors of the Chinese Academy of Sciences was held in Kunming, Yunnan. More than 270 representatives from 12 countries attended The meeting. This conference brought together the latest research and development results reports of many top experts at home and abroad in the related fields of ultraviolet light-emitting diode materials and devices. [4]
At present, ultraviolet light-emitting diodes are the main trend in the development of nitride technology and the development of third-generation semiconductor material technology, and have broad application prospects. In order to speed up the development of the third-generation semiconductor solid-state ultraviolet light source, the Ministry of Science and Technology of China is striving to implement the key R&D project of the "third-generation semiconductor solid-state ultraviolet light source material and device key technology" (2016YFB0400800). The support of the national key R&D plan and the holding of the International UV Materials and Devices Seminar will accelerate the realization of the market application of China’s third-generation semiconductor UV light sources, and drive the development of China’s UV semiconductor light-emitting diode materials and device technologies and their industrialization. positive effect.
Organic Light Emitting Diode
In 1987, Kodak company Deng Qingyun and others successfully prepared low-voltage, high-brightness organic light-emitting diodes (OLED), showing the world for the first time the commercial application prospects of OLED'". In 1995, Kido published in Science magazine The article on white light organic light-emitting diodes (wOLED), although not very efficient, has opened the prelude to OLED lighting research. After decades of development, the efficiency and stability of OLEDs have already met the requirements of small-size displays and have been affected by many Favored by high-end instrumentation, mobile phone and mobile terminal companies, large-size technology is also improving day by day.
The development of OLED materials is the foundation for the vigorous development of the OLED industry. The earliest OLED light-emitting materials were fluorescent materials , but the upper limit of the theoretical internal quantum efficiency of fluorescent materials due to spin inhibition can only reach 25%. In 1998, Ma, Forrest and Thompson, etc. successively reported the application of phosphorescent materials in OLED materials, which opened the way for breaking the law of spin statistics and using 100% of the energy of all excitons. However, phosphorescent materials also have certain problems. Because they contain precious metals, they are expensive and the stability of blue light materials has stagnated for a long time.
In 2009, Professor Adachi from Kyushu University in Japan introduced thermally activated delayed fluorescence (TADF) materials into OLEDs for the first time. This type of material has a very low single triplet energy gap, and can achieve 100% theoretical internal quantum efficiency through the reverse intersystem crossing of triplet excitons (RISC). The material system and device structure are becoming more and more perfect, making OLEDs emerge in the display field. On the other hand, WOLED has a series of advantages such as high luminous efficiency, adjustable spectrum, less blue light component and surface light source. As a high-efficiency light source with low color temperature and no blue hazard, it is expected to become a new trend in healthy lighting in the future.
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