klehman(at)albedo.net
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 Posted: Tue Oct 16, 2012 3:57 am Post subject: Making a LED landing light flash -topic creep |
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Is white the best color for a wig wag?
It made some sense not to diminish tungsten light with a color filter
and of course LED research seems to be concentrated on white (all
colors) light. However I wonder if a less natural yellow-green color
from LED's might make a better wig wag during daytime. For example my
master warning is a 10mm LED that flashes red and green (no pause
between colors) and I perceive it as more attention getting than white
or a single color. Eyes tend to be more sensitive to yellow green.
Ken
On 15/10/2012 11:05 PM, Robert L. Nuckolls, III wrote:
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<nuckolls.bob(at)aeroelectric.com>
At 07:02 PM 10/15/2012, you wrote:
>
> <emjones(at)charter.net>
> > I recently fitted an LED driving light into my wingtip. I am now
> interested in making it flash so I am more visible in the pattern.
> What is the best/cheapest way of doing this? I have seen the Wig Wag
> schematic but I only have one light and from what I read, it requires
> two lights to work.
> I have experimented with this and it look like doubling the rate is
> the best way to go if you have only one lamp. Just leaving out the
> other lamp leaves a whole lot of empty time to not-be-seen. Try it.
> You'll like it.
Agreed. I don't recall the authoritative source but
waaaayyyy back when, we were advised that cockpit
warning lights should be flashed at about 3 to
3.5 flashes per second with 50% duty cycle for
maximum attention getting effects.
I was told that's the number that works best for
intensity modulation (on-off) as opposed to 1 to
1.5 per second for position modulation (wig-wag).
Back when I worked with attorneys wrestling with
grade crossing accidents and various visibility
issues, we learned that visual acuity for 20/20
observer was about 1 arc-minute or 1/60th degree.
To perceive that a wig-wag grade crossing signal
(8 or 12" roundels on 30" centers) was not a steady
red light, the 20/20 observer who was paying attention
under good visibility conditions had to be less
than 8000' away. For the wig-wag to get some attention,
required about 3 arc seconds or a sight distance
of about 2800 feet. Of course, there are a dozen
other variables that drive the situation down-hill
from there.
If your wig-wags are on wing tips of an RV or
25 feet apart (10x the center distance on a
grade crossing wig-wag) then you can expect
pretty good attention grabbing presentation
in clear visibility to other pilots at about
28000 feet or 5+ miles and the 1 to 1.5
transitions/second values apply.
For intensity modulated warning systems (strobes,
rotating beacons, etc) the numbers are better
especially at the faster rate more likely to
grab attention. Unlike the wig-wag that simply
morphs into a steady light beyond a certain
distance, the strobe's on-off behaviors can
be detected from much greater distances.
Bob . . .
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