1 Airport requirements for navigation lighting systems
a) The mark is obvious. The aeronautical lamps that can clearly distinguish the flight area from other non-flight areas are not interfered by other ground lights in the specified flight area, or do not cause visual errors due to insignificant signal identification; b) high luminous efficiency and soft light. The lamp itself is required to have high luminous efficiency, sufficient brightness, clear light color, good resolution under certain visibility, and energy saving. At the same time, the light is required to be soft and not dazzling, to avoid visual fatigue of the flight personnel; c) waterproof and heat dissipation performance is good. The moisture of the lamp will affect the insulation performance of the whole line, increasing the possibility of failure in flight, so the lamp must have better waterproof and heat dissipation performance; d) have a certain mechanical strength. The mechanical strength requirements for the luminaire are: a certain degree of corrosion resistance and collision resistance. However, it is required that when the aircraft is impacted and crushed, the aircraft will not be damaged and the flight accident will occur; e) the structure is simple, durable, easy to disassemble and repair, the system works stably, the fault is less, and the all-weather full-time flight guarantee flight . The price is relatively cheap.
2 airport navigation lighting equipment use status and shortcomings
At present, the lamps for airport navigation lighting equipment mainly include incandescent lamps and bromine tungsten lamps (a kind of gas discharge lamps), which are two kinds of light sources. The color of the light source is approximately white light, and a colored glass filter is added outside the light source to obtain different colors. The light is used to mark the various directions of the airport and the runway. It has the following disadvantages: a) low light efficiency and high energy consumption: the luminous efficacy of the incandescent lamp is 7. 3 18. 6 lm / W, the luminous efficiency of the bromine tungsten lamp is 18 21 lm / W, filtered through the filter mask The light effect after light will be further reduced. In order to achieve sufficient luminous flux, the power of a single lamp is usually 50W and 100W. It is calculated by the general airport runway of 2 500m. There are about 350 types of sign lights, plus the circuit loss. The power of the whole system reaches 30 60kW. The light efficiency is low. Nengda is the biggest shortcoming of current airport navigation lighting equipment lamps; b) Short service life: At present, the life of incandescent lamps and bromine tungsten lamps is not more than 1 000h. Take the lamps used in the airport as an example, PD24-100 incandescent lamps The service life is only 200h, JF6. 6A65W type bromine tungsten lamp has a service life of only 500h. The short service life results in lower reliability of the entire airport navigation lighting system, and also increases the workload of daily maintenance; c) complex structure and low strength: Incandescent lamps and bromine-tungsten lamps are all packaged in glass bulbs. The glass bulbs and the filaments inside are easily damaged or even broken when subjected to vibration and collision.
3 LED lighting development and status quo
LED is an electroluminescent light source, which is a semiconductor device that directly converts electrical energy into light energy. It is a solid-state light source. Its electrical characteristics are consistent with ordinary diodes, and its illumination principle is that a forward voltage is applied across the P-N junction, and holes in the P region flow to the N region; and electrons in the N region flow to the P region. Then, as the coincidence of the fractional carriers and the majority carriers, energy is released; one part of the energy is converted into heat and the other part is converted into light.
LEDs were introduced more than 30 years ago. Due to the limitations of manufacturing technology at the time, the brightness of the LEDs was small, and only one color of red, the luminous efficiency was only 0 4 lm / W, so it was only used for small indications for a long time. In limited fields such as light sources and alphanumeric displays. After the mid-1990s, the new material AlInGaP brought a huge breakthrough to LED technology, increasing the luminous efficacy of red and amber LEDs to 10 20 lm / W, similar to incandescent lamps currently widely used in signal lights, and even more it is good. With the rapid development of wide bandgap semiconductor materials, these electronic materials (mainly including SiC, ZeSe, diamond and GaN) have led to the further development of LEDs, which can be made into blue and green using the band gap of GaN. With the improvement of the combined semiconductor thin film technology formed by the gas phase, organic chemical vapor deposition (MOCVD) technology has made great progress, and the LED manufactured by this method not only has a significant improvement in luminous intensity, but also increases the range of color variation. It has changed the situation that LEDs only have a red series, which has eliminated a major obstacle for the further development of LED in various fields.
The emergence of different color LEDs meets the demand for different color light sources for airport navigation lighting equipment. At the same time, the significant increase in LED light efficiency has made it possible to apply LED lighting in airports. LEDs have the following advantages over incandescent and bromine-tungsten lamps currently in use:
a) High light efficiency and energy saving: the current red LED light efficiency can reach 100 lm/W, the green LED can reach 50 lm/W, and the white light LED can achieve 50 lm/W, which greatly exceeds the ordinary incandescent lamp 7 3 18. 6 lm / W level, and some people predict the current development speed of LED technology, by 2010 and 2015, the efficacy of white LED may reach 150 200 lm / W, far exceeding all current lighting sources Light effect. Currently in the experimental LED airport navigation lighting equipment, the whole set of equipment power is only a few kilowatts; b) long service life: the life of ordinary incandescent lamps and bromine tungsten lamps is less than 1 000h, some are only 200h, and LED The service life can be as long as tens of thousands of hours. The improvement of service life will inevitably greatly improve the reliability of LED airport navigation lighting equipment and reduce maintenance time; c) The structure is firm and small: LED is a solid-state light source encapsulated by epoxy resin, and its structure is free of glass bubbles, filaments, etc. The damaged part is an all-solid structure and therefore can withstand shocks and shocks without causing damage. In addition, the LED illuminator is close to the point source, which is convenient for the luminaire design, and is easy to be made into a thin luminaire, saving installation space.
4 LED airport navigation lighting equipment use and problems to be solved
At present, the application of LED in the airport is still in the experimental stage. In addition, the white light LED developed in China has low light efficiency and high import price. There are still some problems to be solved in the LED to be officially used in the airport: a) luminous efficiency problem At present, the light effect of LED lighting needs to be further improved. The light intensity of a single LED is small. Only when multiple LEDs work at the same time can it be applied to the light source of the airport lighting equipment, further improving the light efficiency of the LED light and the light intensity of the single LED. The key to promoting the promotion of LEDs in airports. The most important way to improve the luminous efficiency of LEDs is to improve the structure and manufacturing process of semiconductor luminescent materials and LED chips; b) Circuit design problems: high-power semiconductor lamps can use either high-power illuminating tubes or low-power illuminating tubes. However, whether it is to use a high-power tube or a small power tube, the key to the technology is to solve the power conversion problem and the heat dissipation problem of the lamp body. There are few light-emitting diodes for semiconductor lamps manufactured by high-power LEDs, and there are no peripheral components, and the structure is simple and easy to manufacture. However, the current high-power LEDs are relatively expensive, so the cost of the lamps is high. There are many tubes for making high-power semiconductor lamps with low-power LEDs, so a series/parallel structure is needed to increase the light intensity. LED lamps are usually composed of multiple LEDs, which are current-driven devices. Therefore, power converters The function is to transform the original power supply to provide a stable one-way driving current for the LED, and to ensure that the LED operates under relatively high luminous efficiency and relatively low light decay. This requires a reasonable layout of the LED, according to its characteristics, design a reasonable drive, control and protection circuit; c) directional problem: because the light emitted by the usual LED is relatively concentrated in a small solid angle range, The direction is strong, and there is a problem of viewing angle. The pilot also generally reflects this problem during the test. In order to solve this problem, it is necessary to conduct research from the arrangement of LEDs and the scattering and refraction of light. For example, a parallel lens is produced by a convex lens or a Fresnel lens, and then the beam is re-diffused and deflected by a pincushion lens, a wedge prism, or the like to generate a light distribution that satisfies various standard requirements of the marker lamp. This requires a unique secondary optical system design for the LED sign light. Only by thoroughly solving the directionality problem of LED can the pilot clearly see the LED sign light at different heights and angles; d) heat dissipation problem: the thermal structure design of the lamp body is another problem that cannot be ignored in the manufacture of semiconductor lamps. . Although the LED is a cold light source, it is not a hot body during operation. However, the resistance heat generated when a current flows through the light-emitting diode causes the lamp body to heat up. The light-emitting diode made of the semiconductor material will rapidly age at a high temperature, and the light effect is lowered. To slow down the light decay of the LED, so that the semiconductor lamp has a long service life, the temperature of the LED tube must be lowered. To reduce the temperature of the die, the temperature of the lamp body should be lowered, and the LED and the lamp body should be reduced. The thermal resistance between them requires solving the heat dissipation problem of the semiconductor lamps; e) Anti-lightning prevention problem: the airport is generally built in an open and flat place, and no tall buildings or high lightning protection facilities are allowed around, so the control tower and the supply are controlled. The potential for lightning strikes on electrical equipment is increased, and semiconductor LED chips are easily broken down by higher voltages and stronger currents. Therefore, reliable grounding, reasonable arrangement of the shape of the ground network to meet the equipotential needs is an important measure to ensure the safety of the lighting system distributed in the vast open area airports; f) cost of production: due to the low light efficiency of domestic LEDs, especially It is a white LED, so the LEDs used in airport lighting equipment are usually imported. Taking white LEDs as an example, a single LED is equivalent to 9 yuan, and in order to achieve a certain light intensity, a runway edge light needs 144 LEDs. 1 296 yuan, this is only the cost of LED. Such a price creates a big obstacle for LEDs to be put into use at airports. To solve this problem, we can only start with scientific research and manufacturing processes. On the one hand, we will strengthen scientific research, improve the light efficiency and light intensity of domestic LEDs, reduce the number of LEDs in each lamp, and on the other hand, improve the process level and increase the production scale. , reducing the cost of a single LED.
5 Conclusion
Despite the development of LED airport navigation lighting equipment, there are still a series of technical key issues to be solved, but with the rapid improvement of the light-emitting diode die, the LED packaging and lamp manufacturing process are further improved, some economic and technical The obstacles will be gradually eliminated. It is believed that in the near future, LEDs will be widely used in airport navigation lighting equipment.
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