Aircraft cockpit floodlighting is used to illuminate areas such as dashboards, left/right consoles, and central consoles. Reasonable cockpit floodlighting ensures that pilots can see fast, see clearly, and are less prone to fatigue. Otherwise, the errors in interpretation and manipulation will increase, that is, the "human error rate" will rise. According to the statistical analysis of flight accidents abroad, the accident caused by “human error†accounted for 40% of all accidents and the helicopter reached 70%. The cockpit floodlighting is unreasonable, causing visual fatigue is one of the direct causes of "human error."
This paper first analyzes the relevant standards for cockpit lighting and proposes the design requirements for floodlighting. Secondly, combined with the characteristics of the LED light source itself, the advantages of LED application in floodlighting are analyzed. Thirdly, the design of floodlighting is analyzed in detail from the aspects of light color, Power Supply, layout and dimming control, and a scheme is formed: white LED, 28VDC power supply, PWM dimming. Finally, the appropriate luminaires are selected for simulation testing to verify the rationality of the design.
1. Cockpit lighting related standards
The existing standards for civil aircraft cockpit lighting are broadly divided into airworthiness regulations and industry standards. The Airworthiness Regulations CCAR-25 have only made qualitative requirements for cockpit lighting and have not yet submitted quantitative requirements. At present, most of the national military standards and aviation industry standards have been formulated in the 1980s and 1990s. The lighting technical parameters mentioned in these standards are not fully compatible with the requirements of modern civil aircraft. The most representative of the foreign standards are the US military standards and SAE standards. Most of these standards are formulated after 2000, which can better reflect the level of modern lighting technology and can be used as a design input for floodlighting.
By comparing the relevant standards, according to SAE-ARP4103 and SAE-ARP1161, the quantitative design requirements for cockpit floodlighting are given, as shown in Table 1.
Table 1 Floodlighting design requirements
2. Advantages of LEDs for floodlighting
The rational design of floodlighting involves more practical engineering problems, and the choice of lighting source is one of the more prominent problems. According to the survey, most of the current civil aviation aircraft use traditional incandescent lamps (especially halogen lamps) or fluorescent lamps as the cockpit illumination source, while new types of civil airliners, such as the A380 and B787, use LEDs to varying degrees. LEDs are introduced into aircraft cockpit lighting because of its advantages in certain aspects, such as energy savings, long life, stability and shock resistance.
The LED uses a combination of minority and multi-child in the PN junction to achieve illumination, and the emission wavelength corresponds to the forbidden band width of the PN junction. The LED is used as an illumination source with the advantages of small size, high reliability, cold start, good brightness adjustment, and safer operation of low voltage DC. LED is a primary light source. In the process of illuminating, electric energy directly becomes light energy. When it is kept at the same brightness as ordinary incandescent lamps, its power consumption is only one tenth of the latter. LEDs are solid-state light sources with no moving parts and fragile parts (such as filaments) for good vibration resistance. The life of LEDs can generally reach 20,000 to 100,000 hours, much higher than incandescent lamps, and the response speed is fast. Compared with fluorescent lamps, LEDs do not contain mercury that is harmful to human health and are a non-polluting source.
The use of LED light sources to improve the performance of lighting systems is the development direction of aircraft lighting technology. Due to the high reliability of LEDs (the MTBF value of floodlights provided by foreign suppliers can reach 50,000 hours), the failure rate of aircraft lighting systems can be greatly reduced, and the maintenance cost of aircraft can be reduced.
3. Design analysis of LED floodlighting
3. 1 light color analysis
Throughout the development of aircraft cockpit lighting, there are four kinds of light colors such as red light, white light, blue white light and night vision green. GJB455-88 believes that the cabin lighting can be selected from red, white and blue and white, and its chromaticity coordinate range is specified. SAE ARP1048 and SAE AS264 only mention red and white light, and only require red wavelengths above 600 nm. MIL-DTL-7788H requires four colors of light.
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