introduction Aircraft lighting is an important branch of lighting technology in aviation flight technology. The aircraft lighting technology of each period reflects the characteristics of lighting technology to some extent. The light source is the core of lighting technology, and its revolution has driven the development of lighting technology. In 1879, Edison invented the first generation of electric light source - incandescent lamp. In 1908, the practical tungsten lamp was introduced, which opened the era of electric lighting. The original aircraft lighting used tungsten light, built-in special reflective structure, due to tungsten wire. The reason for high temperature evaporation is only about 1 000h, which needs to be replaced frequently, and the luminous efficiency is only 10~20 lm /W. After 1960, halogen lamps began to appear in aircraft lighting systems. Due to the reversible chemical reaction between the internal halogen gas and the tungsten wire, the evaporation of the tungsten wire was suppressed. The life of the halogen lamp was increased to 2 000 h, and the luminous efficiency was about 20 ~ 33 lm /W, the performance of the incandescent lamp is relatively improved, and the current navigation lights still use halogen lamps as the light source. The second generation of fluorescent lamps appeared in 1940, with an efficiency of about 50 to 80 lm / W, and a life of 5,000 h, but the light intensity is small, and it is mainly used for interior lighting in aircraft lighting. In 1991, the third-generation light source H ID lamp (high-pressure xenon lamp) began to appear in the aircraft lighting system. The H ID lamp has a luminous efficiency of 80~100 lm /W, which is 4 times that of the halogen lamp and has a life of about 3,000 hours. It becomes a landing light. Universal light source for high-intensity external lighting fixtures such as taxi lights, runway turn lights, and sign lights. H ID lamp uses high-pressure gas to discharge and emit light, which has good anti-vibration performance. However, due to the high-voltage power supply, the light source and the power supply cable have certain safety hazards. The driving power supply is more complicated, and the electromagnetic interference generated is large. The shielding measures, and the power efficiency is only about 40%, most of the electrical energy is converted into thermal radiation and ultraviolet radiation. LED lighting technology is a new type of lighting technology that has emerged in recent years. It uses a fourth-generation light source, the LED Electroluminescent Light Source (LED), which has low voltage drive, high luminous efficiency, and good color rendering. The advantages of adjustable chromaticity, small size, easy integration, long life, etc. represent the development direction of lighting technology and an inevitable trend of advanced aircraft lighting technology. 1. Introduction to the development of aircraft exterior lighting systems The aircraft exterior lighting system refers to the part of the aircraft lighting system used to provide external lighting. It is an important part of aircraft lighting, which ensures the safety of the aircraft during the operational phases such as take-off, cruise and landing. In the early days of aviation technology, the external lighting system of the aircraft was very rudimentary. In order to ensure the normal flight of the aircraft under different climatic conditions, the requirements for the external lighting system of the aircraft were gradually improved. In 1921, LC We inberg first proposed the idea of ​​landing/sliding lights [1]. In 1925, the father of aviation lighting, Warren Grimes, used tungsten lamps as the light source to develop the first landing/sliding for the Ford Tri- mo tor aircraft. The lamp, due to the scattered light from the tungsten lamp, the structure of the tungsten lamp has been improved, and the reflection structure has been added inside the lamp to design a special light collecting performance and more suitable for landing/sliding lights. Tungsten wire [2]. With the increase in the number of aircraft, the space density of the aircraft is getting larger and larger. In order to enable the pilot to find nearby aircraft in time to avoid collisions, Grimes proposed the navigation light structure of the red-green-white tri-color system to mark the outline of the aircraft. And the direction of navigation, red and green two color lights are obtained by the tungsten lamp and the corresponding color lampshade. Later, designers proposed a high-intensity stroboscopic anti-collision/strobe light system that works in conjunction with the navigation lights to enable pilots to spot nearby aircraft in high-speed flight situations. After long-term development, the aircraft exterior lighting system has gradually improved, including landing/sliding lights, running to turn lights, navigation lights, anti-collision lights/strobe lights, ice detector lights, sign lights, etc. In conjunction with the realization of various functions, the layout of the aircraft exterior lighting system is shown in Figure 1. 2. Technical status of aircraft exterior lighting systems At present, the external lighting of the aircraft mainly uses light sources such as incandescent lamps, HID lamps, and xenon lamps. Navigation lights and ice detectors usually use incandescent or halogen lamps. Due to their short life and low luminous efficiency, the filaments are often damaged in high vibration environments, and the navigation lights are left red and green, so they must also be halogen. The lamp is equipped with a filter of corresponding color, which has a complicated structure and low efficiency; the HID lamp is usually used for the sign light, the landing/sliding light, the runway turning light, etc. The HID lamp has high luminous intensity and high efficiency, and can meet high brightness and highness. Illumination requirements for illumination, but the start-up time is very long, usually achieve stable light output after starting 15m in, the life is only about 4 000h, need to be replaced frequently, HID lamps need to add complex boost drive on the aircraft 115VAC power supply system The circuit can be used, which reduces the efficiency of the system, increases the load of the aircraft, and increases the electromagnetic interference to other systems. The infrared radiation of the HID lamp, the incandescent lamp and the halogen lamp makes the working temperature of the lamp high, and the installation is also relatively high. High requirements; strobe lights/anti-collision lights usually use xenon lamps, the working principle is similar to HID lamps but not identical, causing electromagnetic interference and other similar problems [3], discharge The life of xenon lamps is more limited under flash work. The commonly used red anti-collision lamps need to be red light in addition to the white lamp xenon lamp, so the efficiency is very low, and the red lamp cover has unstable light transmission characteristics. The impact is great [5]. Incandescent, halogen and HID lamps do not achieve their goals very efficiently in achieving specific areas or specific light distribution illumination, and they do not satisfactorily meet the two sides of navigation lights when incandescent or halogen lamps are used as navigation lights. The light distribution of the angle requires that there is a problem of incorporation of light intensity; when the H ID lamp is used as a landing light/sliding light or a runway cornering light, the problem of uniformity of illumination cannot be effectively solved, and the structure is complicated, and multiple lamps are required to be installed. Achieve landing functionality. It can be seen that aircraft exterior lighting systems using incandescent lamps, halogen lamps and HID lamps have disadvantages such as low efficiency, complex driving, slow response, short life, safety hazards and low reliability, which cannot provide high efficiency and high safety. Sexual, highly reliable external lighting. 3, the rapid development of LED lighting technology LED lighting is a new type of lighting technology that uses semiconductor materials to inject light into the light. The core light-emitting device is a semiconductor material light-emitting diode (LED), also known as a solid-state light source. The emergence of high-power white light LED has caused a new revolution in the field of lighting. Semiconductor luminescence technology began in the early part of the last century. In 1907, scientists discovered the luminescence of semiconductor materials for the first time, which led to the study of semiconductor luminescence mechanism. In 1962, Nick Ho Lonyak invented the first light-emitting diode (LED), and then with the advancement of technology and technology, the luminous efficiency of LEDs is also increasing, but the luminous frequency is limited to infrared, red and other bands. Until 1993, Japan's Nicia Company took the lead in preparing a GaN-based heterojunction blue LED with a power efficiency of 10%, and first obtained a white LED in 1997 using a package of blue LED + yellow phosphor, and the luminous efficiency was about 10lm /W, afterwards, the researchers obtained white light with high color rendering performance through RGB three-color LED combination and ultraviolet LED + phosphor [6]. The development history of illumination source is shown in Figure 2. In recent years, driven by strong policies and funds, LED lighting technology has developed rapidly. In the past few years, the efficiency of white LEDs has been increasing, gradually surpassing incandescent lamps, fluorescent lamps, HID lamps, etc. The power efficiency laboratory value of white LED is close to 50%, and the luminous efficiency can reach 161lm /W. The luminous efficiency of industrialized high-power white LED has exceeded that of fluorescent lamps and HID lamps, reaching 120 lm /W or more. Currently LED lighting Technology has been widely used in street lamps, LCD large-screen TVs and notebook backlights, automotive lighting, landscape lighting and other fields. In the field of aircraft lighting, LED lighting technology has enormous application potential, and the use of LED lighting technology can help improve the overall performance of aircraft lighting systems. In cockpit lighting, LED light guides, overhead lights/floods provide high-efficiency display instruments and a low-fouling visual environment; in cabin lighting, LED floodlights, reading lights, etc. can enhance the cabin Comfort, Mood Light ing based on the adjustable color of LED color can realize the scene of cabin lighting, providing passengers with a relaxed and entertaining environment. In external lighting, LED light source can improve the efficiency and reliability of the system. Sex and safety, providing pilots with comfortable and effective visual information; using LED light sources in emergency lighting saves power and increases system life and reliability. 4. Advantages of LED lighting technology applied to aircraft exterior lighting Aircraft exterior lighting is characterized by high power, strict light distribution requirements, harsh environment, and high technical requirements. From the previous analysis, it can be seen that traditional lighting technology can not effectively meet the requirements of external lighting, and LED lighting technology has many traditions. The advantages that lighting does not have provide an opportunity to improve the external lighting system of the aircraft. (1) High efficiency and energy saving The halogen lamp commonly used in navigation lights has a luminous efficiency of only 20~33 lm /W. The luminous efficiency of H ID xenon lamps commonly used in landing lights, taxi lights and runway cornering lights is only 80~100 lm /W. The luminous efficiency of high-power white LED has reached 120 lm /W or more, and the luminous efficiency can theoretically reach 283 lm /W. With the improvement of technology and process level, there is still much room for improvement. An external lighting system with an LED source will save at least 20% of the power and greatly reduce the load on the power system. (2) Advanced optical design The small light-emitting area is an important feature of LED. The traditional incandescent lamp filament is long, and the gas discharge area of ​​the gas discharge lamp is large, so the light-emitting area is relatively large. The illumination optical design of the large-area light source is very complicated, and there is no effective design method. The external illumination system of the aircraft has high requirements on the light distribution. When the large-area light source is used, the optical structure of the luminaire is complicated and the light utilization rate is very low. 1W high-power LED light-emitting chip is 1mm 1mm 0. 1mm, the LED light-emitting area after packaging is only about 1. 5mm 1. 5mm, the light-emitting area is very small, approximate point light source, in practical application, according to the external lighting system The specific lighting requirements of various types of lamps, the optical structure of lenses or reflective bowls designed by mature non-imaging design methods, combined with such optical structures and LED light sources can provide high-performance lighting fixtures. Figure 3 is a three-dimensional free-form non-imaging optical design method proposed by the research team led by Professor Luo Yi of the State Key Laboratory of Integrated Optoelectronics of Tsinghua University. This method can effectively solve the lens design for a given three-dimensional illumination [6] - [7]. With the development of non-imaging optical design technology, optical system design methods for a given illuminance or a given light intensity distribution have matured, and these methods combined with the characteristics of LEDs can design a high-performance LED external lighting system. Taking navigation lights as an example, the airworthiness standard stipulates the minimum light intensity distribution at various angles. Incandescent lamps and HIDs are difficult to design a reasonable optical structure due to the large light-emitting area, which optimizes the light intensity distribution, and the advantages of LEDs. One of them is its convenient optical design. Using a design method similar to the beacon light [8], a navigation light system that meets the airworthiness standard can be designed. 
