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Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445878 - 12/15/17 11:12 PM

Quote:

I hear there have been issues calibrating the intensities of LED runway lighting, too.




I'm not surprised. A colored LED will have a different spectrum than filtered incandescent. LEDs will tend to be on specific line of frequency rather than "broadband". Test instruments and the Mark1 eyeball show different intensities. IIRC, the eyeball tends not to respond to having all the power in a few lines of color (LED) rather than spread out (filtered incandescent).


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Bob Dubner
Super Imperial Member


Reged: 08/31/01
Posts: 4759
Loc: Extreme Upper West Side
Strobing Runway Lights [Re: Russell Holton]
      #445884 - 12/16/17 12:16 PM

This is deja vu all over again.

Once upon a time, when traffic lights were colored glass filters over white
incandescent bulbs, some blue was added to the green to make them more
visible to people with red-green color blindness.

Obviously, LEDs are they way to go, now; too many reasons for using them to
ignore -- lifetime, power consumption, and so on.

But it's going to take a few years to sort out. Clearly, the aliasing
wagon wheel effect of the LEDs seen through a propeller arc is unacceptable.
That's going to require DC drivers, or driving different LEDs in the clusters
at different phases and/or different frequencies, or something I haven't
thought of in the thirty seconds I've been considering the problem.

And the fact that LEDs radiate in narrow bands that some people might be
insentive to is also tricky. There aren't any white LEDs; they work by
having the LEDs, usually blue or ultraviolet, stimulate flourescent material
that radiate in the red, blue, and green, which combined produce a
pseudo-white. Now that a true safety need is being demonstrated, one can
only assume and hope that the folks developing those phosphors will continue
their efforts in making the radiation more broad-band.

Another thing that has to be kept under control is over-enthusiasm for cheap
bright light. A couple of streets in Brooklyn were outfitted with
experimental LED street lights. The street was lit up like an operating
theatre; pretty much everybody hated it. It seems to me that even the safety
argument for that much light is bogus; really bright light means really black
shadows that you can't see into because your eyes aren't dark adapted.


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Terry Carraway
Top Gun


Reged: 06/02/04
Posts: 7098
Loc: Maryland
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445919 - 12/18/17 09:27 AM

I see a flicker with the LED tail lights on some vehicles.

When they are moving across my field of vision, I get the flicker.

But I am also someone who used to have a heck of a time with a CRT with 60 Hertz refresh rate. I needed to set it to at least 72 Hz.

--------------------
Terry
Mostly 0W3


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Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: Strobing Runway Lights [Re: Terry Carraway]
      #445932 - 12/18/17 12:54 PM

Quote:

I see a flicker with the LED tail lights on some vehicles.

When they are moving across my field of vision, I get the flicker.




That's probably the PWM - especially with lights that are both tail and brake lights. The PWM would be more noticeable in "tail" (brake off) mode.



Quote:

But I am also someone who used to have a heck of a time with a CRT with 60 Hertz refresh rate. I needed to set it to at least 72 Hz.



I can see it. I can put up with it if I'm helping someone, but if it's to be "my" machine, I up to to 72Hz.


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Gil Buettner [KAUW]
Top Gun


Reged: 05/16/04
Posts: 2847
Loc: Gateway to the Northwoods
Re: Strobing Runway Lights [Re: Bob Dubner]
      #445942 - 12/18/17 05:39 PM

Bob, here in snow country there is another problem with LED traffic lights. They don't generate the heat to melt snow off of the lenses.

--------------------
-Gil


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Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: Strobing Runway Lights [Re: Bob Dubner]
      #445945 - 12/18/17 06:08 PM

Quote:

But it's going to take a few years to sort out. Clearly, the aliasing wagon wheel effect of the LEDs seen through a propeller arc is unacceptable.
That's going to require DC drivers, or driving different LEDs in the clusters at different phases and/or different frequencies, or something I haven't thought of in the thirty seconds I've been considering the problem.




I'm thinking about changing out the dimmer system to something that works on a different frequency. I'm not sure as there is any simple solution that preserves the dimming function.


Quote:

And the fact that LEDs radiate in narrow bands that some people might be insentive to is also tricky.



I'm sure this is review for you, but as far as I know, there's only two sources of light radiation: back body (thermal) and what I'd call "atomic".

The former is what happens when you heat something so hot it give off light. (Incandescent, halogen, etc.) That kind of light is smooth. (Looking at the spectrum.)

The other kind is the photons given off when an atom drops from a higher level of energy to a lower state. That photon wavelength is specific to the quantum states involved - so a given chemical always gives off the same line(s) of light. (Multiple lines many be involved for a single pure chemical as there may be multiple levels of energy involved.) This is true of florescent, mercury vapor, LEDs (both "direct" and phosphor-based, etc, etc. About the only difference is the method used to get the atoms into the higher energy state in the first place.

The only way to get "white" phosphor is to combine elements so the result looks white to the human eye, even though it's still made up of discrete lines.

This seems to be well established science for florescent lights. I'm not sure why it's a challenge for LEDs - at least the phosphor types.


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Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
Re: Strobing Runway Lights [Re: Gil Buettner [KAUW]]
      #445996 - 12/19/17 01:54 PM

Quote:

Bob, here in snow country there is another problem with LED traffic lights. They don't generate the heat to melt snow off of the lenses.




Gil -- I'm seeing helicopter pilots using NVGs (Medevac) complaining that many obstruction lights are going LED...and goggles don't pick up more than half of those...and same with lights on hospital helipads. Hard to stop the train of "progress", I guess.

--------------------
www.scottdyercfi.com


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Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #445999 - 12/19/17 02:31 PM

Quote:

obstruction lights are going LED.



Given the level of effort it takes to get up there to change the bulb, I don't blame them.


Quote:

..and goggles don't pick up more than half of those...and same with lights on hospital helipads. Hard to stop the train of "progress", I guess.



Part of me wants to point out that's what happens when you rely on a convention that's not part of any standard. The goggles were sold with the idea that the lights would have IR radiation, but that's probably not in any current standard.


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Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
Re: Strobing Runway Lights [Re: Russell Holton]
      #446007 - 12/19/17 08:04 PM

I'll blame the turkeys who designed and installed lights that are not fit for the intended use, especially on hospital heliports and with obstruction lights. A reasonable engineer would have foreseen the shortcomings, don't blame the nvg makers who designed the equipment when there were no LEDs.

I'd take the case of a medevac pilot who dies after hitting a stealth tower cloaked with nvg-invisible lights.

"Oh well" won't play well to the jury....


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Russell Holton
AVSIG Member


Reged: 07/07/05
Posts: 14136
Re: Strobing Runway Lights [Re: Scott Dyer [HPN/NY]]
      #446010 - 12/19/17 08:34 PM

Quote:

I'll blame the turkeys who designed and installed lights that are not fit for the intended use,



Please define "intended use". More to the point, can you find any specification that lists a requirement to have IR emitters? Because that's where an engineer is going to start.


Quote:

A reasonable engineer would have foreseen the shortcomings,



And how would an "reasonable engineer" know that? Again, where is the specs for nav lights that indicate that?


Quote:

don't blame the nvg makers who designed the equipment when there were no LEDs.



Which raises a question - did the nvg makers ever claim you could see nav lights? Or was that discovery made somewhere else (sales or user) and somehow turned into a practice that was unsupported by official documentation?


Quote:

"Oh well" won't play well to the jury....



Hmmmmm. A nvg that's completely blind to something that someone not wearing them could see. Seems like the "reasonable" test belongs somewhere else. Sure, you could make all the nav lights have IR, but what else (non-nav lighted objects) could be out there that wouldn't have a IR emitter yet are perfectly visible to the naked eye? And whose bright idea was it to fly with this blindfold that ignores visible light?


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