All aircraft require lighting. And when it comes to lighting, we are seeing a trend toward more light emitting diodes (LEDs) being used on aircraft these days. How do LEDs work, and what makes them so attractive to owners/operators? These are some of the things we will cover in this article, as well as maintenance considerations to keep in mind when working with these lighting products.
The LED boom
Up until around 12 years ago, LED use on aircraft was very limited. The main reason was that white LEDs were not available before then. That all changed in 1993 when Shuji Nakamura, a researcher at Nichia Chemical Industries in Japan invented the blue LED and shortly thereafter, the white LED.
With the development of white LEDs, we started to see an expanding use of LEDs in aviation, but the growth was a bit slow. As recently as five years ago, LEDs were still somewhat of a novelty in aviation with limited use. Back then you might have seen a few LED lighting products - mainly reading and overhead lights. Nowadays, LEDs have made significant inroads into aviation. They continue to gain market share with more and more LED lighting products introduced each year. From navigation lights and beacon lights, to LED strips that replace fluorescent tubes, many more choices are available to the owner/operator.
How they work
Simply put, as the name implies LEDs are diodes that produce light. They are semiconductors and function like other diodes in that current can only flow through them in one direction. Unlike incandescent and fluorescent bulbs that create light within a vacuum, LEDs are solid-state lamps. They produce light when current passes across layers of their semiconductor material. Unlike filament type bulbs that send electricity through a thin wire causing them to generate radiant heat when they produce light, LEDs are illuminated by the movement of electrons within the semiconductor material.
Why all the hoopla?
There are several advantages to LED lights. First of all, compared to filament lights, LEDs can seem virtually indestructible. Because they are solid-state lights, they aren't susceptible to shattered glass or broken filaments. This makes them more hardy in the aircraft's vibration and shock environment.
LEDs also operate cooler than incandescent bulbs. The light created by LEDs is created by the electrical flow through the diode, not the heating up of a thin filament. Therefore, there is less radiant heat produced than incandescent bulbs.
LEDs also are more energy efficient. They consume less power in part because energy is not wasted by generating radiant heat. LEDs consume approximately 10 percent of the current draw of conventional lights at the same light output.
Another advantage of LEDs is their long service life. LEDs can have a service life of up to 100,000 hours, making them attractive to use in areas which are difficult to access.
Another advantage of LEDs is their range of colors. Unlike other lights that must use tinting or filters to produce lighting effects, LEDs can be manufactured in different color configurations by changing their chemical composition. This allows for more flexibility in interior lighting design.
Uses in the aircraft
There are many uses for LEDs on aircraft. Companies such as B/E Aerospace, EMTEQ, and Whelen are offering more and more products each year that incorporate LEDs. Examples include upwash/downwash, reading lights, instrument lights, emergency lighting, and even position indicating (navigation and beacon lights). Some lighted instrument panels now incorporate LEDs.
One interesting product I recently learned of is an LED product that was designed to replace fluorescent tubes. This is being manufactured by Muskego, Wisconsin-based EMTEQ as a drop-in replacement for fluorescent lights (used for Boeing 747 upwash/downwash applications).
Since LED lights are touted as being hardy, mechanics may be prone to believe that there are not any maintenance considerations to consider when working on them. But there are a few things to keep in mind.
Probably the most important factor to consider when working with LED lights is that with LEDs, proper polarity is essential. LEDs have an anode and cathode side just like regular diodes, and need to be installed correctly to operate. If replacing an LED, you must ensure the polarity is correct. The anode side is installed toward the positive, and the cathode toward the negative.
There are several ways you can determine the polarity of a replacement LED:
- Look for a line in the metal inside the LED (this may be difficult to see). This line is closest to the anode side of the LED.
- Look for a flat spot on the edge of the LED. This flat spot is on the cathode.
- Look at the length of the leads. When taking a LED out of a package, you will notice the leads are of different lengths. The longer lead is the anode side and the shorter is the cathode.
In some cases, you may need to adjust the direction of the light. This is because unlike incandescent or fluorescent bulbs, LEDs tend to be limited in the area of light focus. For example, in the case of EMTEQ's LED product replacing fluorescent tubes, direction of the installation is important. "You need to ensure that the lights are placed at their optimum angle," explains EMTEQ's Beth McGowan. It is a matter of rotating the strip so that the light is focused on the area where the lighting is required.
No product is perfect, and LEDs do have some drawbacks to consider. First is the price. Although the price point of LEDs gets lower as more products are being produced (as with any emerging technology), LED bulbs are considerably more expensive than other "traditional" lighting products at this time. For some, this can be a limiting factor not to install LED lights on their aircraft. But the total cost of operation, not just the initial cost of purchase, should be factored in.
Another drawback of LEDs is their dimming over time. Toward the end of their life cycle, LEDs lose some of their brightness. This problem is magnified if the LED is operated at temperatures higher than their design specification.
Another consideration when looking at LEDs is their light output. Although a white LED is brighter than a comparably sized, conventional incandescent bulb, it's not as bright as a high-output Krypton or Xenon bulb. This may be a factor where bright light is required.
There are other applications in the hangar where LED lights are making inroads. Task lighting such as flashlights is one example. UV LED light products have also been developed for use in dye-penetrant inspections. The main advantage of LED inspection lights is that the bulbs are solid state and more durable than filament types. A drawback, as discussed earlier, is that the light output is less than with Xenon or Krypton bulbs.
This has been a primer on LED lights. Armed with information on LED lights, you can better enlighten your customers on the advantages and disadvantages of these emerging products. AMT