See the light

From the cockpit to the cabin, LEDs are increasingly being used to illuminate the latest aircraft interiors. Mike Richardson discovers how they are helping design engineers tailor interior lighting solutions and improve the passenger's flying experience. This is your captain speaking: sit back, relax and enjoy the flight while our cabin interior ‘mood' lighting system creates an atmosphere to soothe even the weariest of passengers. In this scenario, cabin lights are tailored to suit your individual needs so that your food no longer looks green, and you no longer awake from a deep sleep bathed in the glare of spotlights. Even the likelihood of air rage can be subdued by selecting a more favourable and softer glow of ambient lighting. This ‘chilled out' state of consciousness is brought to you by the latest innovations in solid state lighting (SSL), a technology that is increasingly being used to shed light on some of the latest cabins and cockpits as design engineers look to venture into LEDs as opposed to traditional incandescent light sources. Beyond the requirements for more controllability, power efficiency and environmentally friendly operation, the airline operators' chief demands centre on the desire to offer more comfort to its long haul passengers and create an impression that you are flying and yet still in the comfort of your own home. Diehl Aerospace claims to have positioned itself as a lighting solutions partner for aircraft manufacturers. As well as providing the avionics for equipment systems, the company is also a supplier of coloured LED lighting systems to Airbus and Boeing. Diehl Aerospace's marketing manager Guido van Geenen, identifies two main trends that apply to both short and long range flights. “Firstly, the increasing value of in-flight comfort has become more noticeable and in this respect mood and atmosphere lighting concepts are important factors,” he begins. “One popular buzzword is ‘flying in your home', but the airline's predominant desire is in the creation of pleasant lighting effects that help reduce problems associated with jetlag. “The second trend concerns their crucial role in improving power efficiency. This will provide longer product lifecycles, which in turn improves the future prospects of SSL adoption. Diehl Aerospace has followed this development and offers its cabin lighting upgrades to provide airlines with the tools to equip their cabins with mood lighting products.” Van Geenen acknowledges that like all high-tech products, there are clearly obstacles but they are nevertheless conquerable: “The A350 XWB and 787 Dreamliner are the best examples of new aircraft where both platforms have been successfully equipped with all-LED products supplied by Diehl Aerospace,” he claims. The acquisition of the Airbus factory in Laupheim, Germany last October and the formation of Diehl's Aircabin were crucial milestones for the company, he notes. This has paved the way for Diehl in becoming a tier one partner to the major aircraft manufacturers in the field of air cabin integration. The biggest business challenge for Diehl lies in satisfying the newly established market of SSL consumers. In van Geenen's mind, it's essential to meet current and upcoming customer requirements, as the anticipation of these demands will provide the company with its most important mission. “LED technology will evolve into an international market entry strategy as it progressively reaches wider endorsement,” he avows. “The economies of scale will lead to a market concentration of suppliers and strongly influence the development of the manufacturer's brand. However, it's important to understand that in order to achieve an aesthetically beautiful cabin atmosphere, it's essential to master the art of optics, electronics, hardware and software first.” Power behind the light More and more general lighting manufacturers are recognising the important role that the suppliers of optics, power ICs and passives play due mainly to increases in light output per die achieved by power LED manufacturers and the subsequent cost, performance, control and efficiency improvements. Able to mix RGB light to create ambient mood lighting in cabins, the growth of power LEDs into aerospace applications will require technical improvements at the avionics system level as well as at the power LEDs themselves, if SSL is to realise its potential. According to National Semiconductor, all LEDs work best when driven with a constant current source. This is because its colour can change when small variations in driving current occur. LEDs often support varying system voltages and forward voltages, which can further cause variations in LED colour and brightness too. National's voltage regulators are said to provide the benefit of constant current source to single or arrays of LEDs, enabling colour and brightness matching over a wide temperature range. National sees a customer demand for reduced system size and weight, as well as the ability to enhance controllability and increase power efficiency. Its systems application engineer for lighting, Christopher Richardson, says that the barriers customers must overcome in order to get their product to market, “Are in finding an effective way of communicating with all the LED lamps to achieve the control of colour changing and fine dimming without adding more wiring, which would mean added weight and cost. Thermal management is always an important factor for SSL too as it requires effective cooling and, in case over-temperature occurs, a control loop to reduce power consumption and LED current. Any overheating can significantly reduce the lifetime of the SSL.” Richardson reckons customers want solutions that no longer require aluminium electrolytic capacitors because they dry out and fail, making them the limiting factor for longer lifetime applications. “They also want the ability to change the colour temperature of white light, or even change the colour,” he adds. “This requires multiple LEDs of different colours and demands a balance in the cost and complexity of the electronic drive solution.” Whilst the demands for smaller footprint, higher reliability/efficiency, and lower cost are ever present in SSL development, Richardson adds two more: increasing integration and faster time to market. “Increasing integration reduces the overall component count, which is significant as each additional component potentially reduces the lifetime/liability of an application,” he confirms. “Faster time to market is becoming essential in practically all applications.” To speed market entry, Richardson has received positive feedback from LED designers after the introduction of National's WEBENCH LED Designer. This free online design tool is said to significantly accelerate design work, helping engineers select from, and design with, hundreds of high brightness LEDs in minutes. The tool offers instant access to the latest SPICE models, parametric data and package information, enabling designers to simultaneously compare the performance of various devices in multiple circuit requirements. “Another way to shorten the design cycle is through reference designs,” he concludes. “A number of manufacturers, including National, offer reference designs for many applications to give the engineer a quick start. National's LED Driver reference design library currently holds over 40 proven designs for various lighting applications.” www.diehl-aerospace.de
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