Green versus red flares

[Kevin B (RPS Coach)]

In the process of replacing flares, and I noticed that now many brands are offering red and green versions of the same flare (this may not be new, just new to me.) I've read that the green flares are more distinctive and easier for the eye to see. Are there other advantages/disadvantages? Anyone have green flares?

[JohnHuth]

I've never heard of green flares before. There is this phenomenon called the Purkinje shift, where your eyes become more sensitive to the red end of the spectrum in darker conditions - so maybe a green flare is better for daytime conditions?

[EEL]

I've never heard of green flares before. There is this phenomenon called the Purkinje shift, where your eyes become more sensitive to the red end of the spectrum in darker conditions - so maybe a green flare is better for daytime conditions?

I think the issue is not whether certain colors might be more visible, but rather different colors have different meanings. So your flare might be or might not be more visible, but the color would send the wrong message. Could spoil your whole day.

Ed Lawson

[Gillian]

I think the issue is not whether certain colors might be more visible, but rather different colors have different meanings. So your flare might be or might not be more visible, but the color would send the wrong message. Could spoil your whole day.

Ed Lawson

Ed,

I've heard of the white collision flare and red distress, but what I read seemed to indicate that green was just another color for distress. (Kevin posting under G's log in)

[Kevin B (RPS Coach)]

This is one of the ads that I saw from a US retailer:

Pains Wessex Mini-Flare 3, 8 Green Flairs.

* 8 Green aerial stars eject to 60m

* Compact personal distress signal ideal for yachts and dinghies

* For day and night use

* Easy to operate

* Visible for 5 miles (increasing to 10 miles at night)

* Stars burn for 6 seconds at 3,000 candlepower

[EEL]

I've heard of the white collision flare and red distress, but what I read seemed to indicate that green was just another color for distress. (Kevin posting under G's log in)

You may be correct. In the military green flares are used as I recall to indicate safety.

However, I do not believe anything other than a red flare meets CG requirements for a distress flare and for complying with their requirements for a visual distress signal.

http://www.uscg.mil/hq/g-m/mse4/vds.htm#Flares

Ed Lawson

[Kevin B (RPS Coach)]

You may be correct. In the military green flares are used as I recall to indicate safety.

However, I do not believe anything other than a red flare meets CG requirements for a distress flare and for complying with their requirements for a visual distress signal.

http://www.uscg.mil/hq/g-m/mse4/vds.htm#Flares

Ed Lawson

Ed,

It looks that way. Still curious though about the green versions. Even the laser flare comes in a green version from what I have seen.

I went to the Pains Wessex home page and didn't find the green flares. Curious.

[Brian Nystrom]

The fact that green flares cause confusion here is probably a good indication that you should avoid them. Everyone knows that if they see a red flare, it means it's an emergency, so why mess with another color that might not be recognized as a distress signal in an emergency situation?

[Kevin B (RPS Coach)]

The fact that green flares cause confusion here is probably a good indication that you should avoid them. Everyone knows that if they see a red flare, it means it's an emergency, so why mess with another color that might not be recognized as a distress signal in an emergency situation?

It's not a matter of avoiding them as I have no plans to buy them. I want to know why they exist. Just because I and apparently everyone else is confused as to why they exist doesn't mean we have to stay confused.

So, does anyone know about these?

[EEL]

QUOTE(Kevin B @ Jul 1 2008, 07:49 AM) <{POST_SNAPBACK}>

Just because I and apparently everyone else is confused as to why they exist doesn't mean we have to stay confused.

It is odd that there is not easily obtainable info on flare colors.

I may well be in error, but my dim recollection is red is for distress, white is for location, and green is for all OK/Safe.

Ed Lawson

[Kevin B (RPS Coach)]

It is odd that there is not easily obtainable info on flare colors.

I may well be in error, but my dim recollection is red is for distress, white is for location, and green is for all OK/Safe.

Ed Lawson

Ed,

I've seen hints to that effect but nothing definitive. I've emailed the Coast Guard directly to see what they have to say.

[rcohn]

I've never heard of green flares before. There is this phenomenon called the Purkinje shift, where your eyes become more sensitive to the red end of the spectrum in darker conditions - so maybe a green flare is better for daytime conditions?

John,

It's actually the reverse, eyes become more sensitive to the blue end of the spectrum when dark adapted and spectral response peaks in the green. see scotopic response curves, http://hyperphysics.phy-astr.gsu.edu/Hbase...ion/bright.html . You have only minimal sensitivity to red light when dark adapted. Green flares should be more visible night or day.

Ralph

[subaruguru]

I've never heard of green flares before. There is this phenomenon called the Purkinje shift, where your eyes become more sensitive to the red end of the spectrum in darker conditions - so maybe a green flare is better for daytime conditions?

Trying to remember my sensory psych studies from 35 years ago, red simply doesn't bleach out the visual purple in the retina, so that acuity in the dark is maintained. Hence red is used for exit signs in theaters, Audi dashboards, etc. Bright lights nearer the longer wavelengths (green/blue) result in temporary night blindness.

The controversy about whether those bluish xenon headlights are harsher to oncoming drivers than yellower incandescent/halogen ones continues, despite claims that increase in temporary night blindness following exposure to the bluer ones is a function of observers simply STARING at them longer because of their novelty! Hmm....

So maybe a green flare is a bit more visible initially in the dark, but it's apt to reduce the acuity of whoever's looking at it, I fear.

But I could be all wet.

Ern

[scamlin]

QUOTE(Kevin B @ Jun 30 2008, 08:52 PM) <{POST_SNAPBACK}>

Ed,

It looks that way. Still curious though about the green versions. Even the laser flare comes in a green version from what I have seen.

I went to the Pains Wessex home page and didn't find the green flares. Curious.

Kevin:

I seem to remember a review and field test of green vs. red laser flares saying that green has significantly better visibility than red under a variety of condtions. My memory is hazy, but on the order of twice the range. As a side note, the green laser was also significantly more expensive probably due to manufacturing costs since red is the more common color.

If this is true, it may not translate to flare colors.

Scott

[Phil Allen]

Kevin:

I seem to remember a review and field test of green vs. red laser flares saying that green has significantly better visibility than red under a variety of condtions. My memory is hazy, but on the order of twice the range. As a side note, the green laser was also significantly more expensive probably due to manufacturing costs since red is the more common color.

If this is true, it may not translate to flare colors.

Scott

Red "diode" laser's have been around in low to moderate versions for more than a decade (laser pointers anyone?). However, it is only recently (~3 years?) that they've managed to make a cost effective green frequency doubled diode laser with any sort of stability and power. To make the "green" laser, the take an infrared laser diode and double the frequency so that it emits green. So the increased cost is due both to the differences in development "age" and the device complexity. The green is arguable better as the eye is more sensitive to it, as discussed above.

One clear difference between the laser "flares" and trad. flares is that you have to actively point and move the laser flare for it to be effective. In contrast, under good conditions, a trad flare is visible from all directions.

Taking the pointy headed geek hat off now.

Phil

[Nick Schade]

Kevin:

I seem to remember a review and field test of green vs. red laser flares saying that green has significantly better visibility than red under a variety of condtions. My memory is hazy, but on the order of twice the range. As a side note, the green laser was also significantly more expensive probably due to manufacturing costs since red is the more common color.

I remember something similar. As I remember, green cuts through fog better. I don't have any information to back that up.

[Pintail]

Ernie (Mr. SubaruGuy),

With all due respect, as I have written here before -- regardless of BMW's and Audi's predilection for fancy red lighting for their instruments, Cessna dropped red cockpit illumination about forty years ago! I know of <no> modern aircraft that utilises same. If someone sets off an emergency flare, what does temporary loss of night vision matter?

Regarding those new-fangled xenon headlamps, I dislike being on the receiving end of them: they have very sharply-defined beams, so that when approaching a car thus equipped around a bend or on an incline, there is a greater likelihood of being dazzled <before> truly meeting head-on (if you follow my gist?) (I tell you another thing about cars equipped with "daytime running" lights -- they are often aimed too high, thus dazzling the driver in front! I wish drivers would simply use dipped headlights at all times...)

[rcohn]

Ernie (Mr. SubaruGuy),

With all due respect, as I have written here before -- regardless of BMW's and Audi's predilection for fancy red lighting for their instruments, Cessna dropped red cockpit illumination about forty years ago! I know of <no> modern aircraft that utilises same. If someone sets off an emergency flare, what does temporary loss of night vision matter?

From what I understand, that latest versions of military night vision (NV) intensifiers (type IV) have their spectrum shifted towards the red. If I recall correctly (a big if) the reason was that starlight has greater illumination in the red/near IR end of the spectrum. Therefore, some fighter and helicopter cockpits may have the instrument lights shifted toward the blue (no red lights) to prevent blinding the intensifiers.

That is of no importance for kayaking obviously. However, an interesting question is--if a CG helo is searching for you using NV gear, how well will they see a green flare? I have no idea.

Ralph

[scamlin]

OK, as Professor Stoehrer says, the internet makes you smart: I found the reveiw article and as I remembered, green lasers win hands down. Not quite twice the range in the test, but they stopped well short of the max green laser range. 30 miles for the naked eye under bright moonlight ain't bad.

As a bonus, it tested them using Night Vision Goggles (NGV) as well as naked eyes. Interestingly, the earlier prototype green lasers were not visible to the NVGs but the later production models were.

See the excerpt below; for the full article, just follow the link:

"As we got further away than 20 miles (32 km), the ground team required their NVGs to locate our aircraft's strobe in order to sight the lights and Rescue Lasers on us. Otherwise, we were unable to see anything from them on a consistant basis. The red Rescue Laser was visible with the naked eye out to 22 miles (35.4 km), with NVGs out to 28 miles (45 km).

The green laser was going strong with the naked eye at 30 miles (48 km), which is all we had time and resources to test. In fact, the green laser was so easy to see and so distinctive that we used the green laser for locating purposes to identify the location of ground team at the extreme distances when we lost the location after a course reversal. It was immediately noticeable. While a prototype green laser we tested early on was not visible with NVGs, the production model currently available is clearly visible with NVGs (as shown in the image which does not show the flash as that would appear as simply a bright green screen)"

http://www.equipped.org/rescuelaser.htm

Scott

[rcohn]

The green laser was going strong with the naked eye at 30 miles (48 km), which is all we had time and resources to test. In fact, the green laser was so easy to see and so distinctive that we used the green laser for locating purposes to identify the location of ground team at the extreme distances when we lost the location after a course reversal. It was immediately noticeable. While a prototype green laser we tested early on was not visible with NVGs, the production model currently available is clearly visible with NVGs (as shown in the image which does not show the flash as that would appear as simply a bright green screen)"

Be a little careful here. It wasn't clear to me who was doing the testing. The latest NVG gear is not commercially available (at least last time I looked). Older generations were more sensitive to shorter wavelengths (i.e. green). So we don’t know how well the latest NVGs will see green. I would hope the CG has the latest stuff, but who knows?

Ralph

[Phil Allen]

Ralph-

The NVG isn't available but the specs on the latest generation of image intensifiers are since they're used by more than just the military. Here's a comparison chart from the manufacturer Hamamtsu:

The trend is for broader wavelength sensitivity, so the newer generations expand the sensitivity into the infrared while maintaining that in the blue-green. The newest NVG appear to use the broadrange genIII image intensifiers with very fast electronic control to minimize flashout when the light turns bright. So its likely the NVG available and in use by the CG sees green rather well.

That said, I know nothing about whats on the drawing boards at the kinda places where "if we tell you we have to kill you" goes

Phil

[rcohn]

http://www.dontechinc.com/nvf.html

NIGHT VISION SYSTEMS OVERVIEW

NVIS are passive systems, typically helmet mounted binocular image intensification devices that have a very high sensitivity to radiation in the approximate region of 600nm to 930nm (orange to near infrared). The NVIS work by converting photons from the outside night scene onto a micro-displayed visible image. The NVIS will amplify the nighttime scene approximately 2000 times. To protect the image intensifier assembly, the systems are equipped with an automatic gain control (AGC) which will aperture down the NVIS when exposed to bright lights in the region of approximately 600nm to 930nm. If displays or light sources in the cockpit are not properly filtered, the AGC will activate and the NVIS will become proportionally less sensitive to nighttime objects outside of the cockpit. The NVIS are not used to read the cockpit displays (except the original AN/PVS-5), therefore the filtered displays must be visible to the unaided eye.

Avionic NVIS (ANVIS) filtering requirements are more demanding than ground based systems. To achieve NVC for a cockpit environment, there can be little to no overlap between the emissions spectrum of the display or light source and the spectral response of the NVIS. By contrast, by reducing the near IR transmittance to 5% of the total visible component will often meet the minimum necessary requirements for ground based vehicles and equipment. The filtering of commercial light sources and displays is accomplished using near infrared (NIR) absorbing glass, thermoplastic substrates which absorb NIR radiation, or thin film coatings that simultaneously reflect NIR radiation and allow visible light to pass. These filters are designed to absorb or reflect in the deep red and NIR. Often the chromaticity of the display of lighting systems must be adjusted, which can be easily accomplished along with the near IR filtering. By significantly reducing NIR radiation, night vision goggles (NVG) can be used along with electronic display and lighting systems without affecting the nighttime sensitivity of the NVIS. Secondary filtering operations such as EMI/RFI shielding, antiglare/antireflective coatings or contrast enhancement can be added to the night vision filters.

http://www.lumitron.com/new_page_8.htm

There are two types of night vision goggles per MIL-L-85762A: Type I and Type II. The response spectrum and sensitivity for the Type I and Type II goggles are comparable. The Type I NVIS system uses Generation III image intensifier tubes to display the image on a phosphor screen in the users direct line of sight, whereas the Type II NVIS projects the image on a transparent medium in the users line of sight (similar to standard heads-up display technology). The Type II configuration allows for simultaneous viewing of the intensified image and the cockpit displays. The Type I goggle user must look below the goggles' display in order to use the control instruments.

Both goggles are equipped with a minus blue filter for heavy suppression of the visual spectrum before the radiation can reach the image intensifier tubes. There are two minus blue filters available (Class A and Class B ) – long pass filters with a Tp at 625nm and 665nm, respectively. The Class B filter lets less of the visual red spectrum pass; therefore, Class B NVIS is compatible with red cockpit lighting and the Class A systems have a spectrum overlap and cannot be used with the NVIS red lighting.

Spectral response functions found in this document

http://www.gamma-sci.com/PDFs/ANVIS.pdf

also:

http://www.cpctexas.com/home-nvis.htm

http://www.casa.gov.au/download/CAAPs/ops/174-1.pdf

http://www.uscg.mil/directives/cim/3000-3999/CIM_3710_2D.pdf

It has been a few years since I looked at this stuff so my memory was a bit fuzzy. Estended IR range began with Gen III tubes and they have visible sensitivity.

The military NVG goggles are filtered to cut down on the GaAS photocathode visible spectrum sensitivity, they appear to be blind to green light. Again I have no idea what the CG uses but Appendix I of the CG manual might indicate that CG NVGs are also blind to green light.

Ralph