Product Focus: Lighting

With light-emitting diode (LED) technology for cockpit and cabin lighting now the norm for all new-production applications, lighting suppliers are working to develop higher-power LEDs that are brighter and to improve processing techniques that improve color consistency. At the same time, suppliers are taking advantage of digital capabilities from consumer electronics for improved functionality.

"The greatest technical challenges facing the lighting industry relate to improving the efficiency of LED light sources," said Paolo Vanni, engineering technical director for Sirio Panel S.p.A., of Montevarchi, Italy, a subsidiary of Finmeccanica. Sirio Panel will supply an all-LED cockpit lighting system to Airbus for the under-development A350XWB.

"Specific areas we are focusing on include LED chip extraction efficiency, light conversion phosphor efficiency and improved areas of thermal management," Vanni said.

A number of trends are driving growth and innovation in aircraft LED lighting:

(1) LEDs are brighter because they now operate at greater power levels, which means fewer are needed to generate the same illumination; (2) LEDs have better color consistency; and (3) LED lighting arrays have greater functionality because of the incorporation of microprocessors.

"The LED used to be a one-watt device with a certain amount of lumens and that is increasing every year," said Matt Trotter, director of product development for Emteq, New Berlin, Wis. "We’re able to pull more heat away from the junction of the LED so it can run at higher output for longer periods of time."

Thermal management is the key to developing higher output LEDs.

"Much of the evolution of LEDs is in the packaging," said Stephen Scover, vice president and general manager of the lighting division of B/E Aerospace, Wellington, Fla. "As LEDs become brighter and more efficient you can look at smaller assemblies with the same output. The challenge there is thermal management, where you dissipate heat though the back of the assembly rather than through the user interface. You don’t want passengers to adjust their light and burn their fingers."

Scover said B/E’s proprietary heat dissipation techniques have progressed to the point where more costly metallic housings that are used for business aviation lighting are now being designed for commercial aviation in more cost-effective plastic housings. "The tradeoff is only in appearance; you’re getting similar light output," said Scover.

In addition to greater intensity, LEDs color consistency is improving from one production batch to the next. This is mainly seen in the production of white LEDs, where improved manufacturing processes do a better job of depositing a phosphor coating onto a blue LED (creating light in a white wavelength). As a result, white LEDs are finding increasing application throughout the cabin for overhead wash lighting and exit and aisle pathway lighting, as well as some exterior usage in anti-collision lights.

A third and arguably more important trend is the use of miniaturization and functionality from commercial, digital electronics being ported over to aircraft lighting.

"Microprocessors were too expensive a few years ago," said Trotter. "Today we have a wash light with a linear LED display where we use a microprocessor to control dimming and communicate to the cabin management system (CMS) with feedback."

Trotter was referring to one of Emteq’s newest products: the ELW90 LED light assembly for retrofit into business aircraft. It incorporates digital control and RS485 data communications, used for long distance and multi-point applications. The technology allows for direct interface and communication with the CMS, eliminating the need for additional hardware to control the lights and allowing for optimal data transmission performance between multiple devices.

The direct CMS interface includes a reporting system that communicates to the CMS following each command to advise if the command was interpreted and addressed properly. For aircraft without an existing CMS or RS485 bus, Emteq is also developing an analog-to-digital interface bus module where customers can install a potentiometer or analog control to the lights.

The ELW90 light array can be connected in sequence to reduce weight. Said Trotter, "We typically design our lights to carry an amount of current, so we can input power into the first three-foot-long light and then carry that over to the next three lights for 12 feet total, allowing us to minimize connectors and wiring."

Mood Lighting

Like a fine restaurant that imperceptively dims the lights as the evening progresses to create ambiance in the dining room, aircraft manufacturers are taking advantage of LEDs to create their own mood lighting in the cabin.

"We can control color and contrast and intensity in the cabin to simulate everything from sunrise to sunset," said Jeff Johnston, Honeywell product manager for platform components. "As airplane manufacturers become more aware of these capabilities, they are asking for more."

A number of airlines have already installed such LED-driven mood lighting in their cabins, including Malaysia Airlines, Cathay Pacific and British Airways. These three turned to B/E Aerospace for the work.

"Our first program was for (Malaysia Airlines), which recognized the color concept in mood lighting and wanted the light to augment the cabin colors," said Scover. "Then about one and a half years ago, the trend changed to where not everyone wanted color in the cabin, but instead wanted to tone white light where you could have a bright, cooler light for welcoming and departure and a more amber light for dinner time."

B/E Aerospace cabin lighting systems give the cabin crew the option of selecting from six to 12 lighting themes that are controlled through a variety of touch panel displays or membrane-type interfaces.

Aircraft lighting providers are hoping the new capabilities that LEDs afford will get aircraft designers to begin thinking about lighting during the design stage rather than as a commodity, afterthought product.

"The cabin is an integrated system, and while everyone interprets color differently they are realizing that the lighting system is as much of a design as any other product," said Scover. "A lot of lighting is done at the end of the design and then it is too late to take an overall cabin approach."

But while they are asking for more functionality, airframers also need to understand that LED lighting is drastically different than incandescent or fluorescent lighting in a number of ways.

"LEDs are point sources of light versus radiant sources; people think that it functions like a light bulb, but it doesn’t," said Johnston. "It takes optics if you want to spread the light. The fact that these are solid state makes them different, and very thermally sensitive. You must make sure that each LED has a uniform intensity, which means you must manage the intensity balance between old and new LEDs. They have controllers and electronic circuitry that you wouldn’t have with incandescent light.

"Specifications and regulations haven’t been updated to reflect that, particularly with exterior lighting," Johnston added. "LEDs lower their light output over time; they don’t go off like incandescent lights. Specifications will have to address how long you want intensity to meet a certain luminescence because a year from now you might not be able to read a map. Before, failure was defined as either on or off. Now failure is a lot more complicated.

"We find that a lot of customers don’t want to become lighting experts. So they either spec things like they used to do and open themselves up to a broad variety in quality between vendors, or they put their trust in people who they feel have greater technical competence."

Many airframers and airlines are especially concerned about the microprocessors necessary to operate and manage some LED lighting systems, and worry that centrally controlled, bus-linked lighting, for example, adds another layer of complexity and maintenance that didn’t exist with the simple incandescent or fluorescent light.

"The biggest challenge comes from convincing the aircraft industry to accept such solutions in consideration of the certification aspects," said Gabriele Pieralli, regional sales manager for Sirio Panel. "Generally, aircraft manufacturers or operators do not like to spend big efforts in certifying what they consider simple products. Many, if not most, still prefer light units without any intelligence component inside."

Exterior Lighting

The last domain for LED lighting is in exterior applications like anti-collision lights, landing lights, taxi lights, tail lights and logo lights. In many instances, the high-intensity discharge (xenon) and halogen lights used outside the airplane are already giving way to LEDs.

Last summer, Honeywell signed an $80 million contract with Airbus to replace the halogen navigation wingtip lighting on A320-family narrowbodies to LEDs. The contract covers approximately 5,000 forward-fit production and fielded A318, A319, A320 and A321 aircraft types. The technology upgrade covers the forward navigation lights located inside the wingtip that provide recognition lighting in the air and situational awareness lighting on the ground.

Honeywell’s lighting technology upgrade will be incorporated into the Airbus production line this month for all forward-fit A320s. The LEDs will be available for retrofit on A320-family aircraft beginning in April. The drop-in replacement for the existing lighting does not require any aircraft modification.

Honeywell says that the wingtip LEDs will last about 40 times longer than current halogen technology, resulting in lowered maintenance costs. The solid-state lighting will stay on wing up to 20,000 hours before replacement, compared to 500 hours for halogen lights, which is a key improvement for a dispatch-critical item.

The switch to LED-based wingtip lighting will save operators up to $30,000 per aircraft over the aircraft’s lifetime, according to the company.

Avionics Magazine’s Product Focus is a monthly feature that examines some of the latest trends in different market segments of the avionics industry. It does not represent a comprehensive survey of all companies and products in these markets.