LED / Nav lights

On Sat, 20 Mar 2004 00:25:32 GMT, Scott Gettings
wrote:

Sorry this was not so "obvious".

Scroll about 1/4 way down the page and click on the "more" beside the picture
of the nav/strobe light demonstration.

Just went through the information on the page and it looks good as
well as interesting. However I'd like to offer a warning.

The math and resistor rating concern me a tad. I may have misread, or
mis-calculated, but...

It talks about using two LEDs and dropping 7 volts at 0.35 A or ( 350
ma) and using a half watt, 20 ohm resistor.

It mentions the resistor getting hot. It should, they are over rating
the resistor by over a factor of 4 and that is with no safety factor.
It's not uncommon for a resistor to get hot, but they should not get
so hot you have to be concerned about them except in the case of wire
wound power resistors which may actually run quite hot.

R does = E/I and in this case 7/0.35 = 20 ohms but it needs to be
carried one step farther and figure the power as well.

Two ways, the first is simply the voltage times the current. You are
dropping 7 volts at 0.35 A = 2.45 watts.
Another way is P = I^2*R, or current squared multiplied by the
resistance. or (0.35 * 0.35) = 0.1225 * 20 = 2.45 watts.

Normally, we double the rating for safety so you need a 5 Watt
resistor, not a half watt.

You are dissipating 2.45 watts in a half watt resistor.
You could get away with that if the lights were pulsed, but in this
case they are on all the time. That much heat will cause the
resistor value to change and is a definite fire hazard.

Normally the resistor gets too hot and breaks, but I have see the
things start glowing. When they do that the resistance can become
quite low, rather than high and you run the risk of shorting the LEDs
which would increase the current even more.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Scott

Morgans wrote:

"Scott Gettings" wrote

To see an article on using LEDs and inexpensive strobes, feel free to
visit our EAA site, scroll down to the member news area and click on the
obvious link. http://www.eaa724.org/

Scott Gettings
Glass Goose

It was not so obvious to me. How about a direct link, or a clue?
--
Jim in NC

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Checked by AVG anti-virus system (http://www.grisoft.com).
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Ernest Christley wrote:

Scott Gettings wrote:
This site was noticed during my original research. $120 per position
light is not very reasonable in my opinion, when you can get a certified
light for not that much more.
On the other hand you can buy a pair of 1-watt red Luxeons for about $20,
and a single, 3-watt green one for about $15. Their 140-degree
"lambertian" pattern is easily wide enough for nav lights, especially if
you use two of them 90 degrees apart. Most other LEDs have very narrow
visibility geometry and have far less light output. Many trying to use
them have given up.

For strobes, surely you can solder together numerous white LEDs in a
360-degree or other geometry. If a "high-powered" LED produces 4
candlepower (4,000 mcd), you'll still need over 100 of them! Or you can
use a few, newer Luxeon LEDs that are still relatively inexpensive. I
calculated you'll spend about $75 for Luxeons that produce over 400 cp
and only have to assemble a small number of LEDs.

I have no financial interest in Luxeon or any other LED product. My
comments were solely to let builders know there is another viable option
and give them another possibility to save money by building it
themselves.

I'll have to agree with you on the advantage of the Luxeon for strobes.

However, for postition lights, the red and green have to span 110
degrees, and the white taillight has to span 140 degrees. Each one's
light output is to taper in the vertical direction. The individual
LED's are much easier to arrange and aim properly, and 10 or so aren't
that difficult to solder together. My airframe is steel tube, so I
already have a rather large heat sink 8*).

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

Go for it. Remember that the Lambertian pattern Luxeons have a 140-degree
pattern.

Scott

Jerry Springer wrote:

Scott Gettings wrote:
This site was noticed during my original research. $120 per position
light is not very reasonable in my opinion, when you can get a certified
light for not that much more.

Read it again, it is NOT per light it is for both of them. It really is pretty
reasonable when you consider all the enginering and boards are already done.

Jerry

Go for it. I'm sure they are happy to have your money.

Scott

Roger Halstead wrote:

On Sat, 20 Mar 2004 00:25:32 GMT, Scott Gettings
wrote:

Sorry this was not so "obvious".

Scroll about 1/4 way down the page and click on the "more" beside the picture
of the nav/strobe light demonstration.

Just went through the information on the page and it looks good as
well as interesting. However I'd like to offer a warning.

The math and resistor rating concern me a tad. I may have misread, or
mis-calculated, but...

It talks about using two LEDs and dropping 7 volts at 0.35 A or ( 350
ma) and using a half watt, 20 ohm resistor.

It mentions the resistor getting hot. It should, they are over rating
the resistor by over a factor of 4 and that is with no safety factor.
It's not uncommon for a resistor to get hot, but they should not get
so hot you have to be concerned about them except in the case of wire
wound power resistors which may actually run quite hot.

R does = E/I and in this case 7/0.35 = 20 ohms but it needs to be
carried one step farther and figure the power as well.

Two ways, the first is simply the voltage times the current. You are
dropping 7 volts at 0.35 A = 2.45 watts.
Another way is P = I^2*R, or current squared multiplied by the
resistance. or (0.35 * 0.35) = 0.1225 * 20 = 2.45 watts.

Normally, we double the rating for safety so you need a 5 Watt
resistor, not a half watt.

You are dissipating 2.45 watts in a half watt resistor.
You could get away with that if the lights were pulsed, but in this
case they are on all the time. That much heat will cause the
resistor value to change and is a definite fire hazard.

Normally the resistor gets too hot and breaks, but I have see the
things start glowing. When they do that the resistance can become
quite low, rather than high and you run the risk of shorting the LEDs
which would increase the current even more.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com


Sound like good advice. My calculations were based on all the sources I've
found, but the above makes sense with its safety margins.

A 1/2 watt resistor doesn't get scalding hot, but hot enough. Using a
larger-wattage resistor (such as going to 5-watt) is easy, safer and certainly
cheap!

Scott

Scott Gettings wrote:

Jerry Springer wrote:


Scott Gettings wrote:

This site was noticed during my original research. $120 per position
light is not very reasonable in my opinion, when you can get a certified
light for not that much more.

Read it again, it is NOT per light it is for both of them. It really is pretty
reasonable when you consider all the enginering and boards are already done.

Jerry


Go for it. I'm sure they are happy to have your money.

Scott

I am sure they would, My point was you said per unit and I said it included both.
You can use up a $120 worth of time pretty fast trying to trying to hay wire
someting together.

Jerry

Scott,

Thanks for the great information. I really like the new luxeon LED's.
I did a internet search and found that Honeywell has a LED position
light for business jets ......

http://www.grimesaero.com/info/liter...ngposition.pdf

Looks like they using one Luxeon Star with lambertian distribution and
two Luxeon emitters with side emitter domes. They report a total of 9
watts so I wonder if they are using 3 three watt Luxeon III's?

Thanks again for the useful inforation.

--Mike
Sonex #293

Michael Crowder wrote:

Scott,

Thanks for the great information. I really like the new luxeon LED's.
I did a internet search and found that Honeywell has a LED position
light for business jets ......

http://www.grimesaero.com/info/liter...ngposition.pdf

Looks like they using one Luxeon Star with lambertian distribution and
two Luxeon emitters with side emitter domes. They report a total of 9
watts so I wonder if they are using 3 three watt Luxeon III's?

Thanks again for the useful inforation.

--Mike
Sonex #293

You are welcome, and correct the Luxeon IIIs. I wonder how much
Honeywell is charging to put 3 LEDs in their fixture? The Luxeons are
worth about $45 retail.

Scott

Scott Gettings wrote in news:406B6C00.75AB45C3
@cfl.rr.com:


You are welcome, and correct the Luxeon IIIs. I wonder how much
Honeywell is charging to put 3 LEDs in their fixture? The Luxeons are
worth about $45 retail.

Scott


I wonder what they are doing for the Red LED's? Lumiled doesn't seem to
have the Luxeon III emitter in Red or Red/Orange colors, although the 1W
parts are pretty bright. The Honeywell datasheet doesn't show a difference
in current requirements between the RED and Green lights. I wonder what
they are doing.

--Mike
Sonex #293

Ernest Christley wrote in message news:YE47c.1569

BTW, all LED's can be 'overclocked' by pulsing them at a high freqency.
The current rating is limited by the heat it produces. The light is a
function of the voltage. Pulse the light and get more light, but don't
leave it on long enough to burn the LED.

While it is true that you can pulse current to LEDs to achieve a
higher peak output, this does not make it appear brighter to your eye.
The human eye integrates the light output as a time average, so an
LED that pulses at twice the current for 1/2 half the time will look
no brighter than one that is running steady state. In fact, it may
actually be dimmer because LED efficiency can drop at higher currents
due to current saturation of the junction hole/electron pair
generation/recombination function. There is a range of operation at
around 5Hz where pulsed light can appear brighter than steady state,
but this frequency range is too low to be useful because of the
visible flickering of the light. This is due to the psychophysical
characteristics of the human visual system.

Also, the total power dissipated by the LED package is a function of
the average current. Pulsing at twice the current for half the time
dissipates the same power as steady state operation. Proper heat
sinking of the device is important to maintain quantum efficiency
which is highest at cold temperatures and drops as the device heats
up.

PWM of LEDs is really only useful for dimming. At full on, it
operates steady state, and to dim it you start chopping the current
for longer and longer periods of time at the PWM frequency to dim the
device.

Dean Wilkinson
B.S.E.E.
Former Boeing 777 AIMS Display System engineer

Michael Crowder wrote:

Scott Gettings wrote in news:406B6C00.75AB45C3
@cfl.rr.com:

You are welcome, and correct the Luxeon IIIs. I wonder how much
Honeywell is charging to put 3 LEDs in their fixture? The Luxeons are
worth about $45 retail.

Scott


I wonder what they are doing for the Red LED's? Lumiled doesn't seem to
have the Luxeon III emitter in Red or Red/Orange colors, although the 1W
parts are pretty bright. The Honeywell datasheet doesn't show a difference
in current requirements between the RED and Green lights. I wonder what
they are doing.

--Mike
Sonex #293

Must be using 1 watt Luxeons. These are pretty bright at about 44 lumens. I
used 2 ($20 worth) in my left wingtip, and they are so bright you can't look
at them.

Scott