Summary of LED lamp lighting principle, structure and product classification

1. The structure and light-emitting principle of LED

50 years ago, people already knew the basic knowledge that semiconductor materials can generate light, and the first commercial diode was produced in 1960. LED is the abbreviation of light emitting diode. Its basic structure is a piece of electroluminescent semiconductor material placed on a frame with leads, and then sealed with epoxy resin around to protect the internal core wire, so LED has good shock resistance.

The core part of the light-emitting diode is a wafer composed of p-type semiconductor and n-type semiconductor. There is a transition layer between the p-type semiconductor and the n-type semiconductor, which is called the pn junction. In the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, the excess energy will be released in the form of light, thereby 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 no light is emitted. This type of diode made using the principle of injection electroluminescence is called a light-emitting diode, commonly known as an LED. When it is in the forward working state (i.e., a forward voltage is applied to both ends), when the current flows from the LED anode to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, and the intensity of the light is related to the current.

2. Characteristics of LED light source

1. Voltage: LED uses a low-voltage power supply, the supply voltage is between 6-24V, which varies according to the product, so it is a safer power supply than using a high-voltage power supply, especially suitable for public places.

2. Efficiency: Energy consumption is 80% less than that of incandescent lamps with the same luminous efficacy

3. Applicability: Very small, each unit LED chip is 3-5mm square, so it can be prepared into devices of various shapes and is suitable for changeable environments

4. Stability: 100,000 hours, light decay is 50% of the initial

5. Response time: The response time of an incandescent lamp is in milliseconds, while the response time of an LED lamp is in nanoseconds.

6. Environmental pollution: no harmful metal mercury

7. Color: Changing the current can change the color. Light-emitting diodes can easily adjust the band structure and band gap of materials through chemical modification methods to achieve red, yellow, green, blue and orange multi-color emission. For example, an LED that is red at low current can change to orange, yellow, and finally green as the current increases.

8. Price: LEDs are relatively expensive. Compared to incandescent lamps, the price of a few LEDs can be comparable to that of an incandescent lamp. Usually, each set of signal lights is composed of 300 to 500 diodes.

3. Types of Monochromatic LEDs and Their Development History

The earliest LED light source made by applying the principle of semiconductor PN junction light emission came out in the early 1960s. The material used at that time was GaAsP, which emitted red light (λp=650nm). When the driving current was 20 mA, the luminous flux was only a few thousandths of a lumen, and the corresponding luminous efficiency was about 0.1 lumen/watt.

In the mid-1970s, the elements In and N were introduced to enable LEDs to produce green light (λp=555nm), yellow light (λp=590nm) and orange light (λp=610nm), and the luminous efficiency was also improved to 1 lumen/watt.

In the early 1980s, GaAlAs LED light sources appeared, making the luminous efficiency of red LEDs reach 10 lumens/watt. In the early 1990s, the development of two new materials, GaAlInP, which emits red and yellow light, and GaInN, which emits green and blue light, greatly improved the luminous efficiency of LEDs. In 2000, the luminous efficiency of LEDs made of the former reached 100 lumens/watt in the red and orange regions (λp=615nm), while the luminous efficiency of LEDs made of the latter could reach 50 lumens/watt in the green region (λp=530nm).
LED lamps and their luminous principles 1. The structure and luminous principle of LEDs

50 years ago, people already knew the basic knowledge that semiconductor materials can generate light, and the first commercial diode was produced in 1960. LED is the abbreviation of light emitting diode. Its basic structure is a piece of electroluminescent semiconductor material placed on a frame with leads, and then sealed with epoxy resin around to protect the internal core wire, so LED has good shock resistance.

The core part of the light-emitting diode is a wafer composed of p-type semiconductor and n-type semiconductor. There is a transition layer between the p-type semiconductor and the n-type semiconductor, which is called the pn junction. In the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, the excess energy will be released in the form of light, thereby 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 no light is emitted. This type of diode made using the principle of injection electroluminescence is called a light-emitting diode, commonly known as an LED. When it is in the forward working state (i.e., a forward voltage is applied to both ends), when the current flows from the LED anode to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, and the intensity of the light is related to the current.

4. Application of Monochromatic LED

Initially, LEDs were used as indicator light sources for instruments and meters. Later, LEDs of various colors were widely used in traffic lights and large-area display screens, generating good economic and social benefits. Take a 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was originally used as the light source, which produced 2,000 lumens of white light. After passing through the red filter, 90% of the light is lost, leaving only 200 lumens of red light. In the newly designed lamp, Lumileds uses 18 red LED light sources, including circuit losses, with a total power consumption of 14 watts to produce the same light effect.

Automobile signal lights are also an important application area for LED light sources. In 1987, my country began to install high-mounted brake lights on cars. Due to the fast response speed of LEDs (nanosecond level), drivers of following vehicles can be informed of the driving conditions early, thus reducing the occurrence of rear-end collisions. In addition, LED lights have been applied in outdoor red, green, and blue full-color display screens, keychain-type miniature flashlights, and other fields.

5. Development of white light LED

For general lighting, people need white light sources more. In 1998, white light LEDs were successfully developed. This LED is made by encapsulating GaN chips and yttrium aluminum garnet (YAG) together. The GaN chip emits blue light (λp=465nm, Wd=30nm), and the YAG phosphor containing Ce3+ made by high-temperature sintering emits yellow light after being excited by this blue light, with a peak of 550nm. The blue light LED substrate is installed in a bowl-shaped reflective cavity and covered with a thin layer of resin mixed with YAG, about 200-500nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, various colors of white light with a color temperature of 3500-10000K can be obtained.