Compared with traditional light sources, LED light sources have many advantages, which has become common sense. However, LED chips are small in size and compact in structure, and their luminous area is relatively small. It is a Lambert light source with an angle of 180 degrees, and its light intensity distribution is directly proportional to the cosine of the light emitting angle, that is, the illuminance formed by the light emitted by the LED light source on the illuminated surface decreases rapidly with the increase of the exit angle. Obviously, such light source characteristics are difficult to meet the actual needs of outdoor lighting applications. Therefore, in the application of LED outdoor lighting, we must carry out secondary optical design according to different applications and requirements and the characteristics of LED light source, so as to shape and change the light emitted by LED chips, especially the light intensity distribution. Such a secondary optical design process actually belongs to the category of non-imaging optical design.
Non-imaging optical design came into being in 1930s. At first, it was only a practical attempt to improve the performance of some optical products. It was not until 1970s that the theory of non-imaging optical design gradually formed a system. Compared with the design of imaging optical system, the design of non-imaging optical system is concerned with the information transmission of light source, while the design of non-imaging optical system is concerned with the utilization of light source energy and the control of light distribution. Because of its simple structure and high energy efficiency, non-imaging optical system has attracted extensive attention in the design of LED lighting system, and has become a research hotspot, especially for LED lighting system, how to realize the required light distribution on the illuminated surface. Non-imaging optical design can play a key and decisive role.
In the non-imaging optical design of LED lighting system, the basic optical elements mainly include lens, aspherical mirror and refractive plate. The lens can converge or diverge the light emitted by the point light source, thus changing the angle of the light beam, thus achieving the purpose of changing the illumination area and illumination value of the illuminated surface. The shape of aspheric mirror is usually a quadric surface of revolution, and its working principle is completely different from that of lens and mirror. The lens adopts the principle of refraction, while the mirror adopts the principle of reflection or total reflection, and their aperture angles are generally below 40 degrees, while the aperture angles of aspheric mirrors can reach 130 degrees or more. In other words, its light collection ability can be greatly enhanced. As for the main function of the refraction plate, it is to change the emergent direction of light or the beam angle in a specific direction. In fact, it is the peripheral plastic panel of the familiar LED light source system. This kind of plastic panel is classified according to the structure, mainly including tooth-shaped refraction plate, trapezoidal refraction plate and cylindrical refraction plate. Each tooth of the toothed refractive plate is equivalent to a wedge-shaped mirror, and its surface refraction can deflect the light, but it will not change the angle of the light beam, which mainly plays a role in changing the outgoing direction of the light beam. Trapezoidal refraction plate is equivalent to the combination of flat glass and wedge mirror, which can divide a beam of light into three directions, and the light intensity ratio of the beams in the three directions is controlled by the area ratio of the plane and the inclined plane. Cylindrical refraction plate, also called compound eye lens, consists of a series of cylinders, each of which is equivalent to a lens. In the direction of cylindrical generatrix, the light keeps the original incident direction, while in the direction of cylindrical non-generatrix, the lens makes all directions converge or diverge, thus achieving the purpose of expanding the beam angle.
In a word, the design of non-imaging optical packaging system for high-power white LED light source, which is generally optimistic in science and industry, is the technical bottleneck for LED light source to truly enter the lighting market and replace the traditional light source. This research direction is a hot spot to promote the application of LED light source in the lighting field. In a sense, this is also a good starting point for China to break the patent blockade in the field of foreign LED lighting technology, and it is also a good opportunity for us to engage in the downstream of LED technicians and use non-imaging optical packaging system to promote the development of the upstream and middle industries in the field of LED lighting in China. ...