/Aircraft Electrical Systems
   /Lights & Recognition

Light Emitting Diode

Aircraft LED Lights

Several manufacturers are selling LED position and landing lights (including LED strobes too), these are very reliable with a long service life, probably longer than the aircraft. Current draw is much less resulting in thinner cables and there are weight savings too because the high voltage unit is no longer necessary.

LEDs are semiconductors, basically a diode and with a small forward current flow it emits visible light in a different range of colors. Their potential is enormous as a replacement for the incandescent light bulb from the past.

We are going to take a look at this revolutionary semiconductor as a source of light in aircraft and around the house too where energy can be saved and financial gains enjoyed.

Light, Aviation & LEDs

Light is just a stream of photons originating from one point in all directions and it has a certain amount of power too (laser lights are an example of light pointed in one direction only). And as such we can describe some properties of light.

Lumens & candela

The light emitted in a particular direction or steradian (SI unit of solid angle, sr) and is called candela (SI unit of luminous intensity, cd). For example: one candle will emit one candela of light. The term candela is used in aircraft lights.

Lumens (luminous flux) is the amount of light emitted by the source, as perceived by the human eye. And the relation with candela can be defined by: lm = cd × sr. Or: one candela in all directions (our candle) equals cd = lumens / 4 π.

Lumens/Watt: This gives a useful way to indicate the efficacy of lighting products by measuring the total light output in Lumens divided by the power usage in Watts. A higher number means less demand on the electrical system!

Sometimes the term lux is used. Lux (area of luminous flux) is the amount of lumens on a surface per m2 or in formula lx = lm / m2, which is useful for indoor lighting.

Aviation light requirements

For an aviation strobe light (white or red) we need 400 cd (candela) 360° around the aircraft vertical axes and 30° above and below the horizontal plane (some 2000 lm). The navigation lights are a 25 watts incandescent lightbulb producing some 15 lm/W, thus 375 lm in total per bulb. This can also be done with 5 watt LEDs from Lumileds producing 18 - 22 lm/W.

You can see that we need high power LEDs to be able to produce this amount of light. As you can expect these are expensive, although by using GaN (Gallium Nitride) LEDs on a six inch Si (Silicon) waver, production cost is much lower. Which should result in lower prices for the end consumer, but history has shown that these prices drop very slowly.

LED schematic symbol

LED Electronic SymbolLED Diagram

A LED is basically a diode, so in schematics you will see the symbol to the right. The current flows in one direction only from the anode to the cathode. Forward voltage drop varies between 1,7 V to 4,4 V, depending on the color. Aviation uses normally red, green and white LEDs. For the interior of the aircraft, other colors such as blue or green, are used as well.

LEDs are fed by a small voltage and constant current. So connecting them to the aircraft bus without any form of regulation would burn them out almost immediately. They are usually connected in series with a resistor (string) or in parallel strings of series switched LEDs for redundancy. The high power types also need proper cooling if they are to last a long time. Landing and taxi lights are a good example of this.

LED assemblies

Whelen has a number of LED assemblies in their program. For experimental aircraft the MicroBurst™ Series Lighting is of interest, they also have full range or LED lighting for certified aircraft.
But if you are totally into designer aircraft lights then take a look at the Galactica and Aurora series LEDs from Aveo Engineering. They are a beauty for the eye and a must have for your aircraft. Below some examples:

Whelen Microburst

Whelen MicroburstWhelen Microburst

Aveo Engineering

Aveo BeaconAveo Nav

Raylight Aircraft Hermes

Raylight Hermes

Compared to others Aveo lights have the lowest drag of all external lights. This might be an important factor for you, plus they look really great!

LED drop-in

Some companies have developed LED replacements in the form of a bulb. This way you are able to use the existing assembly and when the incandescent bulb dies, can replace it with its LED counterpart. Very helpful!

Written by EAI.

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