What is the light source of LED panel lamp?

LED light source is a light source with light emitting diode (LED) as the luminous body. Light-emitting diodes (LEDs) were invented in the 1960s, and in the following decades, their basic use was as indicator lights for electronic devices such as tape recorders.

This light bulb has the characteristics of high efficiency and long service life, and can be used continuously for 65,438+10,000 hours, which is 100 times longer than ordinary incandescent light bulbs. Scientists predict that in the next five years, this kind of light bulb is likely to become the mainstream product of the next generation of lighting.

English: light emitting diode, abbreviated as LED.

abstract

Light-emitting diode (LED) bulbs are essentially different from traditional incandescent lamps in structure and light-emitting principle.

Light emitting diodes (LEDs) are made of several thin layers of doped semiconductor materials. One layer carries too many electrons, and the other layer forms a positively charged "hole" due to the lack of electrons. When current passes through, electrons and holes combine with each other and release energy, thus emitting light.

People use light-emitting diodes for lighting, mainly by mixing red light, yellow light and blue light emitted by light-emitting diodes. In this way, after red light, yellow light and blue light are "mixed", white light is produced, which is abbreviated as MCLED. You can also use "blue light technology" to cooperate with phosphor to form white light, which is called PC LED. In addition, there is a white light technology that MOCVA directly grows multiple active regions.

basic feature

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1, high luminous efficiency

After decades of technical improvement, the luminous efficiency of LED has been greatly improved. The luminous efficiency of incandescent lamps and tungsten halogen lamps is 12-24 lumens/watt, that of fluorescent lamps is 50-70 lumens/watt, and that of sodium lamps is 90- 140 lumens/watt, and most of the power consumption becomes heat loss. The light efficiency of the improved LED will reach 50 ~ 200 lumens/watt, and its light has good monochromaticity and narrow spectrum, and it can directly emit colored visible light without filtering. All countries in the world are stepping up the research on improving the light efficiency of LED, and its luminous efficiency will be greatly improved in the near future.

2. Low power consumption

The power of a single LED tube is 0.03 ~ 0.06W, and it is driven by DC. The driving voltage of a single LED lamp tube is 1.5 ~ 3.5V, and the current is 15 ~ 18mA, which has fast reaction speed and can work at high frequency. Under the same lighting effect, the power consumption is one-tenth of that of incandescent bulbs and one-half of that of fluorescent tubes. Japan estimates that if you replace half of incandescent lamps and fluorescent lamps in Japan with LEDs with twice the light efficiency of fluorescent lamps. It can save the equivalent of 6 billion liters of crude oil every year. Take the bridge guardrail lamp as an example, a fluorescent lamp with the same effect is more than 40 watts, while the power of each LED is only 8 watts, and it can be changed in 7 colors.

3, long service life

Using electron light field to radiate light, filament is easy to burn, thermal deposition, light attenuation and other shortcomings. LED lamps are small in size and light in weight, and are encapsulated by epoxy resin, which can withstand high-strength mechanical shock and vibration and is not easy to break. The average life span is 654.38+ million hours. The service life of LED lamps can reach 5 ~ 10 years, which can greatly reduce the maintenance cost of lamps and avoid the pain of frequent lamp replacement.

4. Strong security and reliability

Low calorific value, no thermal radiation, cold light source, safe touch: precise control of light type and light emitting angle, soft light color, no glare; Does not contain mercury, sodium and other substances that may be harmful to health. Built-in microprocessor system can control the luminous intensity and adjust the luminous mode to realize the combination of light and art.

5. It is beneficial to environmental protection.

LED is an all-solid-state luminous body, which is shock-proof and impact-resistant, not easy to be broken, and the waste can be recycled without pollution. The light source is small in size, can be combined at will, and is easy to develop into a light, thin, short and small lighting product, and is also convenient for installation and maintenance. Of course, energy saving is the main reason why we consider using LED light sources. Perhaps the LED light source is more expensive than the traditional light source, but it will take one year to recover the investment of the light source, and it will take several times a year to get the net benefit period of energy saving in 4 ~ 9 years.

Luminous principle

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To understand the light-emitting principle of diodes, we must first understand the basic knowledge of semiconductors. The conductivity of semiconductor material is between conductor and insulator.

Among the materials, it is unique in that when the semiconductor is stimulated by external light and thermal conditions, its conductivity will change significantly; Adding a small amount of impurities to pure semiconductors will significantly increase their conductivity. The semiconductors most used in modern electronics are silicon (Si) and germanium (Ge), and their outermost electrons are all four. When silicon or germanium atoms form crystals, adjacent atoms interact with each other, so that the outer electrons become * * * owned by two atoms, forming a * * * valence bond structure in the crystals, which is a molecular structure with little binding capacity. At room temperature (300K), due to thermal excitation, some outermost electrons will gain enough energy to break away from valence bonds and become free electrons. This process is called intrinsic stimulation. After the electrons break free and become free electrons, there will be a vacancy in the valence bond, which is called a hole. The appearance of holes is an important feature that distinguishes semiconductors from conductors.

Because there is a hole in the valence bond of * * *, under the action of external electric field or other energy sources, adjacent valence electrons will fill this hole, form a new hole in the original position of this electron, and then other electrons will transfer to this new hole. This leads to a certain charge transfer. We can use the following formula to calculate the concentration of free electrons in intrinsic semiconductors:

Ni (t) = at3/2e-eg/2kt，

Eg-the energy required for an electron to break away from the valence bond of * * *, in eV (electron volt), also called the forbidden band width;

T- temperature;

A coefficient;

K—— Boltzmann constant (1.38×10-23j/k);

E- the base of natural logarithm.

Since free electrons and holes appear in pairs in intrinsic semiconductors, this formula can also be used to express the concentration of holes. The higher the concentration of free electrons (or holes) in the semiconductor, the stronger the conductivity. At room temperature, the concentration of free electrons in silicon increases by 1 times for every 8℃ increase in temperature. Every time the temperature rises 12℃, the free electron concentration of germanium increases 1 times.

Adding a small amount of pentavalent impurity, such as phosphorus, to the intrinsic semiconductor will result in an extra electron after forming valence bond with other semiconductor atoms. This extra electron can get rid of the bondage and become a free electron with little energy. This kind of impurity semiconductor is called electronic semiconductor (N-type semiconductor). However, a small amount of trivalent impurities (such as boron) are added to the intrinsic semiconductor, because there are only three electrons in its outer layer, which will produce vacancies in the crystal after forming valence bonds with the surrounding semiconductor atoms. This kind of impurity semiconductor is called hole semiconductor (P-type semiconductor). After N-type and P-type semiconductors are combined, the concentration of free electrons and holes at the junction will be different, so both electrons and holes will diffuse to low concentration places, leaving some charged but immovable ions, thus destroying the original electric neutrality of N and P regions. These stationary charged particles are usually called space charges, and they are concentrated near the interface between N region and P region, forming a very thin space charge region, which is what we call a PN junction.

When a forward bias is applied to both ends of the PN junction (a positive voltage is applied to one side of the P-type), holes and free electrons will move with each other to form an internal electric field. Then the newly injected holes recombine with free electrons, and at the same time, sometimes extra energy is released in the form of photons, which is the light emitted by LED. This spectral range is relatively narrow, because the band gap width of each material is different, so the emitted photon wavelength is different, so the color of LED light is determined by the basic material used.

Types of light sources

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Dual primary color phosphor conversion

Double primary color white LED is composed of blue LED chip and YAG phosphor. The commonly used blue chip is InGaN chip, and A 1InGaN chip can also be used. The method of mixing blue chip LED with YAG phosphor has the advantages of simple structure, low cost and relatively simple manufacturing process. Moreover, YAG phosphor has been used in fluorescent lamps for many years, and the process is relatively mature. Its disadvantage is that the efficiency of blue LED is not high enough, so that the LED efficiency is low; The phosphor itself has energy loss; Phosphors and packaging materials will age with time, resulting in color temperature drift and shortened life.

Tricolor phosphor conversion

Effectively improve the color rendering of LED on the premise of high efficiency. The most common way to obtain tricolor white LED is to excite a group of tricolor phosphors which can effectively radiate with ultraviolet LED. This kind of white LED has high color rendering and adjustable light color and color temperature. Using phosphor with high conversion efficiency can improve the light efficiency of LED. However, there are still some defects in the method of ultraviolet LED+ tricolor phosphor, such as the low efficiency of phosphor to convert ultraviolet radiation; Powder mixing is difficult; Packaging materials are easy to age under ultraviolet radiation and have a short life.

Multi-chip white LED light source

White light can also be obtained by encapsulating red, green and blue LED chips and mixing their light. This type of white led light source is called multi-chip white LED light source. Compared with white LED with phosphor conversion, this type of LED has the advantages of avoiding the energy loss of phosphor in the process of light conversion and obtaining higher light efficiency. Moreover, the light intensity of LEDs with different light colors can be controlled respectively to achieve full-color color change effect, and better color rendering can be obtained by selecting the wavelength and intensity of LEDs. The disadvantage of this method is that the semiconductor materials of LED chips with different light colors are very different, and the quantum efficiency is also different. The change of light color with driving current and temperature is inconsistent, and the decay rate with time is also different. In order to keep the color stable, it is necessary to add a feedback circuit to compensate and adjust the three colors of led, which makes the circuit too complicated. In addition, heat dissipation is also the main problem that plagues multi-chip white LED light sources.

Performance index

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(1) color: mainly red, green, blue, cyan, yellow, white and amber.

(2) Current: According to different power levels, commonly used LED currents range from 20 mA to 2 A. ..

(3) Voltage: Voltage is related to color. Generally, the VF of red, green and blue is between 1.8-2.4V; The voltages of white, blue and green are between 3.0 and 3.6.

(4) Reverse voltage VRM: the maximum allowable reverse voltage of LED. If this value is exceeded, the LED may be damaged due to breakdown. It should be noted that some LEDs are not allowed to be reversed (such as OSRAM), and Vrm is generally between 3-5V.

(5) Color temperature: expressed by absolute temperature k, for example, in summer, the sunshine is 5500K at noon and 4000k in the afternoon.

(6) Luminous intensity: calculated by Candela cd. This quantity represents the convergence ability of luminous body in space emission, and it is a * * * description of optical power and convergence ability. The LED I of eg.Ф 5 is about 5mcd.

(7) luminous flux: measured in lumens lm. This quantity describes the total amount of light emitted by the light source, which is equivalent to the optical power. The existing 1W LED luminous flux can reach 80- 130lm.

(8) Illuminance: measured in lux. That is, the luminous flux is evenly distributed on the surface of 1㎡.

(9) Color rendering: expressed by CRI. Luxeon cold white is 70, neutral white is 75 and warm white is 85.

(10) Half-value angle: the angle of twice the center line when the luminous intensity is half of the peak value. According to different applications, it can be divided into high directivity, standard type and scattering type. The half-value angle of eg.XP-C is 1 10.

(1 1) main wavelength

(12) peak wavelength

(13) center wavelength

(14) color purity

(15) Half width

(16) thermal resistance: expressed as RθJC, and the unit is ℃/w. The thermal resistance of foreign power LED is basically within10℃/w. Rebel, white: 9℃/w; XP-G: 6 ℃/W。

(17) life: the time to maintain 70% of the initial luminous flux, which can reach 30.000- 100.000 hours.

merits and demerits

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superiority

1, energy saving and environmental protection

The luminous principle of LED is different from incandescent lamp and gas discharge lamp. The energy conversion efficiency of LED light source is very high, which can theoretically reach 65,438+00% of the energy consumption of incandescent lamps, and LED can also achieve the effect of saving energy by 50% compared with fluorescent lamps. Compared with incandescent lamps with the same brightness, the LED with light efficiency of 75lm/W consumes about 80% less power, and has remarkable energy-saving effect, which is undoubtedly of great significance to China, where energy is very tight. LED can also be used in combination with solar cells, saving energy and protecting the environment. It does not contain itself.

? Toxic and harmful substances (such as mercury) avoid the secondary pollution caused by the mercury overflow caused by the breakage of fluorescent tubes, and at the same time do not interfere with radiation. LED light source is not only more environmentally friendly and energy-saving, but also has a wider color gamut and higher color saturation. More importantly, the service life of LED lighting source is as long as 60 thousand hours, which can completely solve the problem of short service life of traditional bulb light source. 2. Long service life

Under normal circumstances, the light attenuation of LED can be reduced to 70%, and the nominal life is 654.38+ 10,000 hours, which reduces the maintenance work such as replacement frequency.

3. Pure light and color

Because a typical LED has a narrow spectral range, it does not have a full spectrum like an incandescent lamp. Therefore, LEDs can be combined in various ways at will, which is especially suitable for decoration and other aspects. Bright, saturated and pure, without filter, it can be adjusted into different colors with red, green and blue elements, and it can realize changeable, gradual and mixed light effect and excellent color rendering effect. The brightness is continuously adjustable, the color purity is high, and the color dynamic transformation and digital control can be realized.

4, moistureproof, vibration resistance

Because the exterior of LED is mostly protected by epoxy resin, it has good sealing performance, impact resistance and is not easy to be damaged. It can be applied to underwater lighting.

5, flexible size:

Can realize the organic integration with the building and achieve the effect of seeing only the light but not the light;

6. Environmental protection:

No harmful metal mercury, no infrared and ultraviolet radiation. Characteristics of high-power LED and its comparison with other light sources: LED is called "green light source".

7. More changes

LED light source can make use of the principle of three primary colors of red, green and blue, and under the control of computer technology, the three colors have 256 gray levels, which can be mixed at will, that is, 256× 256× 256 =16777216 colors can be generated, forming a combination of different light colors, and realizing colorful dynamic change effects and various images.

8. Advanced technology

Compared with the monotonous luminous effect of traditional light sources, LED light sources belong to low-voltage microelectronic products. It successfully combines computer technology, network communication technology, image processing technology and embedded control technology. , so it is also a digital information product, a "high-tech" technology of semiconductor photoelectric devices, with the characteristics of online programming, unlimited upgrade and flexibility.

9. Other advantages:

Low heat, miniaturization, short response time, etc. All these make LED light source have great advantages and create favorable conditions for its application in actual production and life.

characteristic

1, energy saving 1000 hours consumes only a few kwh (ordinary 60W incandescent lamp 17 hours 1 kwh, ordinary 10W energy-saving lamp 100 hours 1 kwh);

2. The ultra-long-life semiconductor chip emits light, has no filament, no glass bubbles, is not afraid of vibration and is not easy to break, and its service life can reach 50,000 hours (the service life of ordinary incandescent lamps is only/kloc-0.000 hours, and that of ordinary energy-saving lamps is only 8,000 hours);

3. The light health lamp does not contain ultraviolet rays and infrared rays, and does not produce radiation (ordinary lights contain ultraviolet rays and infrared rays);

LED radiator (365)

4. Environmental protection does not contain harmful elements such as mercury and xenon, which is conducive to recycling and will not produce electromagnetic interference (ordinary lamps contain elements such as mercury and lead, and electronic ballasts in energy-saving lamps will produce electromagnetic interference);

5, DC drive to protect vision, no stroboscopic (ordinary lamps are AC driven, which will inevitably produce stroboscopic);

6. High luminous efficiency and low calorific value, 90% of electric energy is converted into visible light (80% of electric energy of ordinary incandescent lamps is converted into heat energy, and only 20% of electric energy is converted into light energy);

7. High safety factor requires low voltage and current, less heat, and will not cause potential safety hazards, so it can be used in dangerous places such as mines;

8. Great market potential, low voltage, AC power supply, battery and solar power supply, which are used in remote mountainous areas, outdoor lighting and other places where electricity is in short supply.

deficient

However, compared with other light sources, LED also has some disadvantages, such as low color rendering in white lighting. The color rendering index of white LED produced by yellow phosphor and blue light is about 80. It can be used as general lighting, but it is not enough for some places that require high color resolution. Although the color rendering index can be improved to above 90 by adding appropriate red phosphor, there is still a certain gap compared with 99 of incandescent lamp, and its efficiency will also be affected. Color rendering can also be improved by RGB color mixing, but more work needs to be done in the popularization and application of technology, so the color rendering of LED needs to be improved. As for the high price and large one-time investment, in fact, considering the comprehensive cost, using LED in many occasions still saves a lot of costs.

kind

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Detection type

Ring light source: directly illuminate the upper part of the measured object.

Strip light source: There are three kinds of lighting effects, namely direct lighting, oblique lighting and photometric lighting.

Line light source: it has a spotlight effect, and high brightness can shorten the exposure time of the camera.

Backlight source: the angle can be adjusted to match the measured objects with different characteristics and working distances.

Backlight: Illuminate from the back of the measured object.

External coaxial reflection light source: the lateral light source can irradiate light on the measured object in parallel through the beam splitter.

Internal coaxial point light source: it needs to be used with coaxial lens.

Hemispherical ridge cover light source: the light source can spread to the uniform irradiation area through the diffusion cover.

Application category

1) indicator category

2)LED backlight

3)LED display screen

4) Backlight and flash of hand-held products

5) Automotive applications

6) General lighting

7) Landscape lighting

8) Special lighting category

Development history

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(1)1962, the joint laboratory of GE, Monsanto and IBM developed a red-light gallium arsenide phosphate (GaAsP) semiconductor compound, from which it can be seen that light-emitting diodes entered the commercial development process.

② 1965, the world's first commercial light-emitting diode was born. It is made of germanium and can emit infrared light. At that time, the unit price was about 45 dollars. Shortly thereafter, Monsanto and Hewlett-Packard Company introduced commercial red LED made of GaAsP material. The efficiency of this LED is about 0. 1 lumen per watt, which is more than 0/00 times lower than that of ordinary 60- 100 watt incandescent lamp.

(3)1968, LED research and development made a breakthrough. By using nitrogen doping technology, the efficiency of GaAsP device reaches 1 lumen/watt, and it can emit red light, orange light and yellow light.

(4)1971,and the industry has introduced the GaP green chip LED with the same efficiency.

⑤ In 1970s, due to the wide application of LED devices in home and office equipment, the price of LED plummeted. In fact, the main market of LED in that era was the application field of digital and text display technology.

The major technical breakthrough in the early 1980s was the development of AlGaAsLED, which can emit red light with luminous efficiency of 10 lumen per watt. This technological progress enables LED to be applied to outdoor information release and CHMSL equipment.

⑦ 1990, the industry developed AlInGaP technology that can provide the best performance of red devices, which is 10 times higher than the standard GaAsP devices at that time.

Today, the most efficient LED is made of transparent substrate AlInGaP material. During the period from 199 1 to 200 1, the further development of material technology, chip size and shape increased the luminous flux of commercial LED by nearly 30 times.

Pet-name ruby1994 Japanese scientist Shuji Nakamura developed the first blue light-emitting diode on GaN substrate, which triggered a research and development boom of gan-based LED. 1996 white LED was successfully developed by Niya Company of Japan.

Attending in the late 1990s, white LED was developed with YAG phosphor excited by blue light, but the color was uneven, the life was short and the price was high. With the continuous progress of technology, the development of white LED is quite rapid. The luminous efficiency of white LED has reached 38lm/W, and the laboratory research results can reach 70lm/W, which is much higher than incandescent lamp and close to fluorescent lamp.

In recent years, with the in-depth research of semiconductor luminescent materials, the continuous progress of LED manufacturing technology and the development and application of new materials (nitride crystals and phosphors), ultra-high brightness LEDs of various colors have made breakthrough progress, and the luminous efficiency has been improved by nearly 1000 times. In terms of chromaticity, all colors in visible light band have been realized, and the most important thing is the appearance of ultra-high brightness white LED, which makes it possible for LED applications to leap into the market of efficient lighting sources. It has been pointed out that high-brightness LED will be one of the greatest inventions after Edison invented incandescent light bulb.

Pay attention to shopping

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With the rush of the market, as consumers, we should choose led calmly and scientifically, and choose the light source lamps with the best cost performance. The following are the basic performances of several LEDs:

1, brightness. The brightness of LED is different, and the price is different. The LEDs used for LED lamps shall meet the laser class I standard.

2. Anti-static ability. The LED with strong antistatic ability has a long service life, so the price is high. Generally, LEDs with antistatic performance greater than 700V can be used for LED lighting.

3. Wavelength. The LED with the same wavelength has the same color. If consistent colors are required, the price is high. It is difficult for manufacturers without LED spectrometers to produce products with pure colors.

4. Leak. At present, LED is a unidirectional conductive luminous body. If there is a reverse current, it is called leakage. LED with large leakage current has long service life.

Light Emitting Diode(LED)

Short life and low price.

5. glow. LEDs with different angles have different light emitting angles. Special luminous angle, high price. Such as the total diffusion angle, the price is higher.

6. Life span. The key to different quality is life span, which is determined by light decay. Small light attenuation, long service life, long service life and high price.

7. wafer. The luminous body of LED is a chip, and the price of different chips varies greatly. Chips in Japan and the United States are more expensive, while the prices of chips in Taiwan Province Province and Chinese mainland in China are generally lower than those in Japan and the United States.

8. Wafer size. The size of the chip is expressed by the side length, and the quality of LED with large chip is better than that with small chip. The price is proportional to the chip size.

9, colloid. The colloid of ordinary LED is generally epoxy resin, and the LED with ultraviolet protection and fire retardant is more expensive. High-quality outdoor LED lighting should prevent ultraviolet rays and fire. Each product will have a different design, and different designs are suitable for different purposes. The reliability design of LED lighting includes: electrical safety, fire safety, applicable environmental safety, mechanical safety, health safety, safe use time and other factors. From the point of view of electrical safety, it should conform to the relevant international and national standards.

Because LED is a new product, China's national standard lags behind, but the country provides product qualification testing. The price of LED lighting with international safety certification (such as GS, ce, UL, etc.). ) and the national product quality certificate is higher, because these products are reliable in safety design. Consumers pay attention to carefully identifying the authenticity of certificates. At present, there are not many manufacturers with international safety certification and national product certification.