Let there be light!

Many customers in the commercial sector are moving from traditional lighting technology to LEDs. Karen Dixon, Young Electronics Group's (YEG) Opto Electronics divisional manager weighs up the benefits

for the aerospace industry.
There are many reasons for switching to LED technology. Some are obviously clear, such as greater energy efficiency and longer life, but additional benefits are less obvious. Particular benefits to aerospace applications include the fact that LED packages are a more robust solution, provide a high light output from a smaller device, weigh less, offer more control over light output, more choice in the colour rendering index (CRI), instant start-up, easy dimming control, no or low UV/infrared emissions and more flexible colour options. Add to this the fact that there are no harmful chemicals in the product - unlike fluorescent lamps for example which have a cost to the environment in their manufacture and disposal - and the case for moving over to LEDs becomes a pretty convincing argument. One important technical aspect in improving the passenger flying experience is colour control. LED manufacturers use ‘binning' to identify the colour and wavelengths of their devices. This makes designing a white or colour changing system easier and can ensure consistency of colour throughout the aircraft cabin. Lens technology is also an important aspect of LED luminaire design. Inherently, LEDs are non-directional in their light output; LED manufacturers use lenses on board the package to create a degree of light dispersion control. However, in some areas additional lenses will be required to diffuse and disperse light to the required area which may mean a reduction in output and possible CRI dependent on the lens quality. Measured in lumens, LED brightness is an area where design engineers have strived to improve their products and there has been rapid progress in this area in recent years. Just two years ago the output on a pure white LED (4,500 Kelvin) was under 100 lumens. Now manufacturers are achieving outputs of over 118 lumens. Smaller packages are now being produced in high power devices; previously the package size was 8mm, now there are devices as small as 3.5mm, but still capable of producing the same lumen output. This has clear advantages in aerospace applications where size and weight are critical factors and empowers designers with more flexibility in light source positioning within the aircraft. A high CRI can be beneficial in an aircraft environment creating a more natural light source. This is particularly important when considering the various mediums and surfaces that passengers and crew are subjected to during flight, such as flat panel screens, controls and instrumentation, books, walkways and dining etc. the CRI of a light source will affect the way a passenger or crew member perceives these images. We are now seeing significant progress with an increase in CRI. This is important as the higher the CRI, the truer the colour will appear when using artificial lighting. At present this is mainly being developed on warm and natural white colours. Some manufacturers are now at 93 CRI, although over the last year we've seen an increase of pure white as well, which was previously 70 CRI but is now at 73 CRI. The only downside on high CRI LEDs is the reduced lumen output. A warm white high power LED running at 350mA with a CRI of 80 would produce an average of 80 lumens, where as the same LED with a CRI of 93, would only produce 60 lumens. So it's a fine balancing act with regard to any lighting environment where LEDs are used. In critical environments such as medical and control environments, a high CRI will be beneficial, but in non-critical areas there is a trade-off: true colour or more light? A high CRI factor results in a lower lumen output, but although greater light output can be achieved by adding more LEDs, the CRI factor will remain the same. The technology is not without its problems and one specific area which is an important issue to the aerospace industry is thermal management. LEDs lose over 80% of their energy consumption through heat and this poses several potential problems, especially for devices in enclosed areas. The efficiency, life and stability of an LED depends a great deal on the optimum operating temperature – too high and all of these factors can be compromised.

Designers are constantly developing new solutions for the efficient transfer of heat ranging from the actual LED package design to special PCB substrates such as ceramics and other heat sinks and highly efficient thermal transfer materials or forced air cooling. YEG Opto says it has considerable experience in helping OEMs overcome the problems of thermal management and work with a range of materials and products which offer solutions depending on the application. Whichever option is chosen, it is clear that the design of the LED and light fitting is an important factor and consideration has to be given to thermal management. LEDs are also voltage sensitive so the lighting systems must be designed to include a stable supply with a voltage above the threshold of manufacturers' recommendation and a current below the rating of the LED. LEDs are also electrical polarity dependant and unlike incandescent bulbs, will not work on reversed electrical polarity. Electrical systems in aircraft can vary from three-phase in heavy transport aircraft to AC power in light commercial aircraft. Therefore, careful consideration needs to be given to the design of the LED driver since a more complex driver circuit will be required to adapt from a three phase system and a stable supply is critical for efficient LED operation. Although LED-based lighting solutions cost more than traditional lighting products at present, they are considered ‘greener' as they use far less energy than existing technologies. LEDs also have a longer lifespan - especially at high power - with an estimated lifetime of 50,000 hours. This adds another benefit in that it reduces the cost of ownership, maintenance and replacement of lighting systems. The development of high power LED lighting solutions means that applications in aerospace have been extended. Driven by demand as manufacturing output increases, the economy of scale will eventually see the cost of LEDs come down. Demand for more energy efficient devices accelerates as energy costs rise, but legislation and environmental issues can be influencing factors on demand, adding momentum to the growth in LED manufacturing output. www.yegopto.co.uk

Related Articles

Work smarter, not harder

Has the next industrial revolution arrived? Mike Richardson hears how National Instruments is using the industrial Internet to help the engineering community connect with Smart tools
9 years ago Features

Testing to the max

Ed Hill speaks to Ian Matthews, NI's Aerospace & Defence Business Development Manager for Europe, to discover some of the latest applications for its testing equipment in the aerospace sector.
10 years ago Features

Connectors can compete

Molex's European industry manager, military/aerospace, Stephen Webster examines the race for radical efficiency improvements in aircraft interconnect design.
10 years ago Features
Most recent Articles

Carter enjoys success at HAI HELI-EXPO event

Acknowledged as the World’s largest vertical aviation conference and trade show, HAI HELI-EXPO 2024 provided precision bearing specialists Carter Manufacturing a perfect opportunity to exhibit its extensive range of aerospace bearing installation, removal and testing tools, along with PMA bearing options.
1 day ago News

Login / Sign up