From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: FW: [LML] For Eric Jones re LED anticollision lights
To: lml
Date: Tue, 19 Aug 2003 19:36:42 -0400
Message-ID: <web-2533754@logan.com>
In-Reply-To: <000a01c36691$af4372b0$0700a8c0@shannon>
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Posted for "Shannon Knoepflein" <kycshann@kyol.net>:

From: Eric M. Jones [mailto:emjones@charter.net] 
Sent: Tuesday, August 19, 2003 11:24 AM
To: kycshann@kyol.net; lml@lancaironline.net
Subject: Re: [LML] For Eric Jones re LED anticollision lights


This is not my project this week or even this month. But here are the
basics--
23.1402 specifies 400 candles EFFECTIVE (perceived) intensity. This is
different from actual intensity.

First- Let's look at a xenon flash lamp (presumably for which the
standard
was written)--It has a very high power  peak then drops off sharply
until it
fails to conduct. The length of the pulse is extremely important for a
number of reasons. The effective intensity is at it's maximum (5X  the
average actual intensity) when the pulse length is infinitessimal and
the
peak is very large. Not the best way to operate a flash lamp.

A discussion of the optimum flash length is too long for this forum, but
at
least we can use this 5X as a general factor. So for short flashes the
average peak intensity required is only 400/5 or 80 candela (more or
less).
Now we're in the ball park.

LEDs pulse beautifully. An LED with a nominal current of 20 mA will
pulse at
100 mA but both the pulse width and the duty cycle must be limited. This
is
where device selection, cooling, optics, and multiple pulses in a 200 mS
window have to be determined.

I do not claim to have figured out the details of this design. Remember
that
other than the white tail light, other anticollision system lights can
be
aviation red--a color easy to achieve in high-power LEDs.

Cost--Currently LEDs are breath-takingly cheap. But you can't buy them
retail in the USA. A really good deal is Besthongkong on eBay (search
for
items sold by him). 50pcs 8000mcd Ultra Bright White LEDs-  BestHK  Item
number: 2548007745 (auction over now but he has more) Buy-it-now price
$3.49. (Astonishing....unbelievable well yes, he adds a hefty "handling"
charge)! Also check the eBay stores of Chi Wing LED product shop,
Dynamic
Electronics and IT Products, and  HKCityShop. There are others.

See:   http://www.periheliondesign.com/redandgreenledpositionlights.pdf

>>CFR 14.23.1401 specifies 400 candles as minimum light output in the
horizontal plane.  In a web >>search, I came up with one high-intensity
white LED, 8000 mcd output, and in quantities of 50, >>which would be
the
minimum required, they're $7 each.  Unless I'm missing something, it
looks
to >>me as if replacing strobes with LED's is going to have to wait a
while
to be cost competitive.

Be aware that figuring out the candelas is the wrong way to make this
calculation. See:
http://www.periheliondesign.com/ledpositionlights.htm

Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net

"In theory there is no difference between theory and practice. In
practice
there is."
     --Yogi Berra

----- Original Message ----- 
From: Shannon Knoepflein
To: 'Eric M. Jones'
Sent: Tuesday, August 19, 2003 6:42 AM
Subject: FW: [LML] For Eric Jones re LED anticollision lights

---
Shannon Knoepflein   <--->   kycshann@kyol.net
-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of
Jim
Cameron
Sent: Sunday, August 17, 2003 11:15 PM
To: Lancair Mailing List
Subject: [LML] For Eric Jones re LED anticollision lights

Eric, CFR 14.23.1401 specifies 400 candles as minimum light output in
the
horizontal plane.  In a web search, I came up with one high-intensity
white
LED, 8000 mcd output, and in quantities of 50, which would be the
minimum
required, they're $7 each.  Unless I'm missing something, it looks to me
as
if replacing strobes with LED's is going to have to wait a while to be
cost
competitive.

Jim Cameron