The luminescence phenomenon of a semiconductor device can be roughly classified into three types in principle: photoluminescence, electroluminescence, and cathode ray illumination, wherein the first illuminating form is when a certain amount of light is irradiated onto the semiconductor, the semiconductor itself Electrons and holes absorb the energy of light and emit light. The second form of illumination is that when a forward voltage is applied to a semiconductor device, electrons and holes move due to the energy obtained, thereby stimulating the luminescence.
Cathodoluminescence is when a certain ray is irradiated onto a semiconductor, the carrier of the semiconductor absorbs energy, which in turn produces a luminescence phenomenon of the composite luminescence.
The LED itself is also a semiconductor device, and the spontaneous luminescence of the LED is due to the combined motion between electrons and holes. Its illumination principle is based on the principle of electroluminescence, and does not adopt a similar illumination principle as a conventional light source such as an incandescent Lamp or an energy-saving lamp. The most important part of the LED is the PN junction, which consists of an N-type semiconductor and a P-type semiconductor, and forms a thin vacuum depletion layer between the P-type semiconductor and the N-type semiconductor. The luminescence process of the PN junction can be roughly divided into three processes: carrier injection at a forward voltage, composite radiation, and optical energy transmission. The semiconductor crystals with very small volume are all encapsulated in a clean epoxy resin. When the electrons are in the wafer, the electrons are released into the hole region and recombine with them. At this time, the holes and electrons disappear simultaneously and photons appear. . The energy of electrons and holes due to complex motion is directly proportional to the electrons and holes themselves. However, the energy of the photons generated by the composite motion is also one-to-one corresponding to the color of the light produced by the photons. Generally speaking, the energy carried by the spectra of different frequencies is different within the spectrum of visible light. Purple light, blue light carries the most energy under normal conditions, while red light and orange light often have the least energy. It is precisely because of the difference in the band gap between different materials that different materials can emit light of different colors.
2 high power LED lighting imaging optics
As a new type of solid-state cold light source, LED has the advantages of small size, long life, high luminous efficiency, energy saving and environmental protection. The broad market prospects of high-power LED lighting have led to a research climax for LED applications, especially in high-power lighting applications, but because the light emitted by the LED chip is Lambertian, such a light field distribution without secondary optical design Direct application to the application of high-power lighting will cause serious light waste. The secondary optical design problem of LED has become a major problem limiting the further promotion of LED in lighting applications. The traditional lighting design method can not make the shortcomings of false prediction. The non-imaging optical theory, lighting design software and computer programming are combined to carry out the secondary optical design of high-power LED lighting fixtures. According to the classic in non-imaging optics. The optical expansion conservation and edge ray principle are used to obtain the surface equation of the lens. Then the discrete points of the free-form lens are calculated by Matlab programming, and the three-dimensional modeling is carried out. The simulation is verified in Tracepro to verify the correctness of the design. The basic package structure of the LED is to encapsulate a semiconductor module with electroluminescence in the epoxy resin, and support the positive and negative electrodes through the pins. The LED structure is mainly composed of a bracket, a silver paste, a wafer, and a gold. Line, epoxy resin consists of five materials, the structure of a packaged high-power LED lamp bead is shown in Figure 1:
Imaging optics of high-power LED lighting fixtures In the design of imaging optics, optical systems are the main imaging tools. The concept of light propagation is mainly studied by the concept of geometric light, and there is no corresponding research on the changes in the transmission of energy in light propagation. However, non-imaging optics is different from imaging optics. From a physics point of view, light rays carry corresponding radiant energy during the process of propagation, and the direction of light propagation is the direction of propagation of the corresponding radiant energy. Therefore, when studying the energy change, the optical system itself is also the medium that transmits the corresponding radiant energy. The propagation process of the light itself is the corresponding energy transmission process. The non-imaging optical theory mainly follows the law of energy propagation. The angle of the entire optical system is studied. The main purpose of the application of non-imaging optics theory is to study the entire illumination system, but this illumination system itself plays a role in controlling the transmission of light energy during light propagation, rather than the imaging effect in imaging optics theory. However, imaging problems cannot be excluded from non-imaging design. Non-imaging optics theory is mainly to solve two kinds of problems. One is how to maximize the energy delivered, and the other is how to Illumination distributions that meet the lighting requirements are obtained on the target plane, which are commonly referred to as collection and illumination in the field of general illumination. The concentrators can be generally divided into two categories, one is called a three-dimensional concentrator, the other is a two-dimensional concentrator, and the two-dimensional concentrator is also called a linear concentrator, and the convergence ratio of the linear concentrator. It is usually expressed as the ratio of the input to the output size on the cross section. For two-dimensional concentrators and three-dimensional concentrators (with axisymmetric properties), the maximum value of c can be obtained, assuming that both the input and output media have the same refractive index, when the circular source is at infinity with iθ The divergence angle emits light. When passing through the optical system, the maximum value of the convergence ratio maxC reaches 21/sini θ, and the angle of the outgoing light and the exit surface converge to form a secondary light distribution. The amount of optical expansion has a certain physical meaning: the amount of optical expansion can be used to evaluate the effect of optical components on the energy efficiency of the entire optical system, and can also be used to describe the characteristics of the beam itself. For specific optical components, the optical expansion It represents the ability of the optical component to absorb the beam, and the concept of optical expansion can be used to determine the degree of matching between the illumination system and the imaging system.
3 high power LED lighting lens model
For an ideal optical system, when the loss of reflection, refraction, scattering, etc. is not considered, the optical spread is conserved after the beam passes through the optical system. In the non-imaging optical design, this is required during the design process. A very important factor to consider is that the optical expansion is as small as possible for the light source in two respects. However, for optical components, the opposite is true. Optical expansion should be for optical components. The bigger the better, of course, the greater the optical expansion is, the better, because the increase of optical expansion does not necessarily bring about the same degree of energy efficiency improvement for the entire optical system, but it will cause complicated optical system design. Degree and production cost are greatly improved, so when designing non-imaging optical system, the concept of optical expansion should be used reasonably to control the trend of light and achieve the conservation of optical expansion in order to obtain the ideal utilization of light energy. And to meet the requirements of the illumination uniformity index, the curve can be rotated for one week to obtain the lens solid mode.
4 high power LED radiator design
The heat transfer of high-power LED lighting fixtures is the heat transfer process of the material under the temperature difference. Whether there is a temperature difference between an object or some objects, the heat will spontaneously occur in one or several ways. The ground passes from a high temperature to a low temperature. There are three basic ways of heat transfer: heat conduction (thermal conduction), heat convection, and heat radiation. Compared with traditional light sources, LEDs are characterized by small size, compact structure, and easy embedding in various lamps. As the carrier of the light source, the heat dissipation design of the luminaire is crucial for the LED to exert its advantages. If the heat dissipation efficiency of the luminaire is designed to be high, it can not only extend the service life of the LED, but also reduce the weight of the luminaire and expand its application range. On the contrary, it will affect the LED's advantages and even become the bottleneck of its application.
This chapter therefore focuses on the design of the heat sink. We know that there are usually two types of heat dissipation: the first one is active heat dissipation, that is, heat dissipation by means of an external fan, water cooling or heat pipe circuit, micro channel refrigeration, semiconductor refrigeration, etc., which is characterized by heat dissipation. High efficiency, small size and compact structure. The disadvantage is that it will increase the additional power consumption, and considering the requirements of the protection level of the lamp, it will increase the difficulty of the design of the lamp; the second is the passive heat dissipation, which mainly relies on the natural convection of the air, and the heat generated by the heat source through the heat sink naturally Dissipated into the air, the heat dissipation effect is related to the size of the heat sink. This method is simple in structure, but the heat dissipation efficiency is relatively low. For the lighting system, since the heat dissipation method is easy to combine with the structure of the lamp, the structure is relatively simple, and no additional power consumption is required, and at the same time, for the comprehensive consideration of processing, material cost, maintenance factor, etc., passive heat dissipation is used. The overall cost is relatively low. At present, the mainstream direction is still the second way. By properly designing the heat sink to meet the heat dissipation requirements of the lighting system to the utmost, the cost can be maximized. A high-power LED Street Light radiator sold by the company is specifically optimized. The heat sink consists of two identical modules. Optimized design of high-power LED lighting fixtures The appearance of the heat sink is shown in Figure 3.
5 Summary
High-power LED is one of the hotspots of research and application in recent years. Especially after the emergence of high-power LED chips, high-power LEDs have a tendency to replace traditional lighting in the field of lighting. At present, LEDs still face problems in driving power supply design, light distribution design and heat dissipation design. In this paper, the second optical design of Lambertian high-power white LEDs is designed to design free-form lenses with uniform circular spots and uniform rectangular spots. At the same time, this paper also studies the heat dissipation of high-power LEDs, and expounds the optimization process of high-power LED flat-panel radiators by using ANSYS optimization function, and gives a specific product design process.
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