Alternative Sources for Nav and Strobe Lights
By Scott Gettings, EAA
Many experimental builders are concerned with the high prices
and lack of flexibility when using products from Whelen or Aeroflash
to light their aircraft. In some configurations, a complete nav/strobe
system can run the better part of $1,000.00. Ouch. I'd prefer
to spend that money on an engine.
Another consideration if you are building
in a "lensed" wingtip light for reasons of appearance
and/or aerodynamics is that the fancy streamlined light housings
are just not necessary. They only add unnecessary cost and weight.
Strobe and nav lights have geometric visibility
and intensity requirements for certified and experimental aircraft.
These specifications are available from multiple sources, including
Aircraft Spruce & Specialty. Basically, you need 360 degree
strobe coverage horizontally, plus 30 degrees of vertical visibility.
The side position lights need 110 degrees of horizontal coverage,
and a white tail position light must be seen from 70 degrees
aft. The intensity requirements are a little vague for experimental
a/c, but 400 candlepower (cp) for strobes and 40 cp for nav lights
appear to be acceptable values. These requirements can be met
in many ways, most often by two "external" wingtip
combination lights, or two internal wingtip and one tail strobe/light.
Light Intensity and Luminescence
In searching for alternative light sources, I found that bulbs
may be rated in lux, lumens, candles, candela, foot-candles,
millicandles (mcd) and candlepower (cp). This is confusing, since
there are not good conversions among these measures. In the most
simple terms, it appears that candles and candela are the same,
and a candlepower is one candle of brightness measured at one
foot. A lumen is the light produced by one candle shining in
one square foot one foot away. A lux is 1 cd at 1 meter. Overall,
it sounds like these terms are pretty similar for our purposes.
You just need real bright lights on airplanes. For more information,
The prices for aircraft strobe systems are truly shocking. For
each location, you need the bulb, its lens, and the power supply.
I began searching for alternatives to high aircraft prices since
strobes are made for many other vehicles at a fraction of the
cost (no surprise here). However, it is quite hard to get light
intensity specs for most non-aviation strobes. If this were possible,
you could probably find acceptable strobe bulbs in the $10-20
range and similarly inexpensive power supplies.More practical
strobe alternatives may include non-standard vendors of bulb-power
supply systems or using LEDs. If you plan to use a conventional
system, you can get inexpensive bulbs that will put out >400
cp for around $30 at:
Rollison Airplane Company, Inc.
or visit us at: www.RLSA.us
Call Rob Rollison to get just the strobe
bulb if you want to mount it separately. Their power supply is
around $150, and will push 3 strobes in flashing patterns. This
is far more reasonable than Whelen's unit at around $400. Rollison
also carries the 16-guage, shielded 3-wire strobe cable for about
$0.50 per foot, which is far less expensive than anywhere else.
You need this shielded cable to avoid RF interference.
Light Emitting Diodes have come a long way in the last few years.
Although LEDs were initially used only for low-light displays,
higher powered lights have now come on the market. Unfortunately,
the cheap "high intensity" LEDs sold by Radio Shack
and most other vendors really don't help us much. Very recently,
a company called Luxeon has produced inexpensive, truly high-intensity
LEDs you can buy over the internet.
LEDs draw amazingly small amounts of current,
such as from 350 milliamps up to 1 amp. Using this little current
not only helps in the total power requirements of a plane, but
also allows much lighter wiring to the nav lights. LEDs also
come on in nanoseconds, last 100,000 hours and have no filaments
LEDs can be used for strobes when both
the intensity and visibility requirements can be met. Depending
on your installation, this may require multiple LEDs and/or a
reflector. For example, replacing a tail strobe/white nav light
could be done with a small cluster of Luxeon LEDs. A strobe using
LEDs will require a device to flash its power supply, which can
be done using a variety of inexpensive options.
The newer, truly high-intensity LEDs can
also easily supply the intensity and visibility requirements
for nav lights. These can be wired directly since no flashing
Hooking up these lights is very simple and inexpensive. There
are two main critical factors: you can't hook them up with the
polarity reversed, and you can't over-drive them past their maximum
current. You can push them a little, however.
You will need to know the voltage drop
of the LED(s), which is called Vf (for forward voltage) and their
normal current in milliamps (ma). This is on their spec sheets.
Typical values might be 3.2 volts and 350 ma. You can hook as
many LEDs in series as you want until the sum of their voltage
drops equals your system voltage. For example, if you used four,
3.2 Vf LEDs in series, you will use up 12.8 volts. You probably
have 13.4 or so volts in your "12" volt system, so
this will work. The basic formula is:
V= V(system)-V(sum of LEDs in series)
If you only want to use 2 LEDs at 3.2 Vf,
and you have a 13.4 volt system, you will have 13.4-2(3.2)= 7
volts. You have to dissipate the remaining 7 volts to avoid exceeding
the maximum current for each LED. You can do this with a $0.10
Ohm's law says V=IR, so
7 volts / 0.35 amps = 20 ohms
Get the nearest 1/2 watt resistor to your
value (22 ohm in this case) and put it in series with your two
LEDs. Be sure to hook up each LED from positive-negative-positive-negative
so you keep their polarity correct. The resistor can be on either
side of the LEDs. The LEDs will get a little warm, but the resistor
will get hot so keep it from touching anything important.
Since the LEDs are so cheap, you may wish
to simply put as many as you wish to "eat up" your
system voltage. If you want to get fancy, you can get small,
constant current drivers from a number of sources (below) to
deliver an exact current. These drivers deliver a constant current
to the LEDs, but seem unnecessary for our applications. If your
system voltage drops momentarily, the LEDs will harmlessly dim
for a second or two. In my experiments, they don't change that
much with minor fluctuations. You can also wire LEDs in combination
parallel and series if needed, as long as the individual Vf and
current requirements are met.
An easy way to build your system is to
place a milliammeter in series with your test circuit of LEDs.
With a direct current readout, you can play with different size
resistors and number of LEDs to optimize your system. You can
also use the simple calculator at: http://www.ledsupply.com/techinfo.html
. This company also offers LED drivers for less than $20. Another,
less expensive supplier is American Backplane, 355 Bantam Lake
road, Morris, CT 06763 (860) 567-1568. Neither source of drivers
is as inexpensive as a resistor - or even another LED!
The only company I found that offers high-intensity, affordable
LEDs is Luxeon. See http://www.lumileds.com/luxeon/products/products_index.html
and download the "Star" datasheet. (Log in as a "guest").
The most usable form appears to be the
Star in the Lambertian (140 degree) light pattern. It is less
than the size of a quarter, has a built-in heat sink, and has
multiple solder terminals to choose from. Luxeon stars come in
1-watt, 3-watt and 5-watt sizes. You can only get red (at this
time) in the 1-watt size. They put out 44 lumens, where the green
1-watt size only puts out 30 lumens. However, you can get a 3-watt
green with around 80 lumens and a green 5-watt with 120 lumens!
The green 5-watt have a voltage drop Vf=6.8 volts, so two of
these could be hooked directly to a 12 V system. In my experiments,
two of the red, 1-watt stars are so bright you can't readily
look at them - bright enough! Other experimenters have measured
the output from these LEDs with satisfactory results: http://www.jbwilco.com/Cozyweb/navstrobe.htm
For strobes, you could use the white Star
III, which produces 80 lumens @1 amp and 3.9 Vf. Five of these
would give you 400 lumens. They cost $15 each, so you could make
a combination tail strobe / position light for $75 that lasted
forever. This is one heck of a lot cheaper than the $180 Whelen
tail combination light I bought - and no power supply or heavy
cable. You just need a simple switching circuit to flash them.
The best place to buy these is at www.luxeonstar.com.
They have the best prices right over the internet.
A combination conventional strobe and LED
nav light wingtip with reflector might look like:
The Luxeon Stars and a sample driver alone are quite small:
Hopefully this short article will give
builders some inexpensive alternatives to their nav and strobe