Talk:Lasers and aviation safety

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[edit] What color is the peak of the dark-adapted eye?

The article mentions that the dark-adapted eye is most sensitive to green light. As of August 12 2007, this is a revert from a previous edit which said the dark-adapted eye is most sensitive to "blue-green" light.

Here is some research to support the use of "green" over "blue-green".

First, the dark-adapted eye (scotopic vision) is most sensitive to 507 nm light. Compare with the light-adapted eye (photopic vision) which is most sensitive to 555 nm light. References: http://micro.magnet.fsu.edu/primer/lightandcolor/humanvisionintro.html (second paragraph after graphic of "Microscopic Anatomy of the Retina") and the "Luminous Efficiency" chart at http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html.

So what color is 507 nm? Obviously, color is perceptual, but here are some references giving ranges.

- The Wikipedia article "Color" has a chart showing blue at about 450-490 nm, and green at about 490-560 nm.

- In the same article, a CIE 1931 color space chromaticity diagram shows wavelength around the outer edge of the curve. Cyan (evenly mixed blue-green) is at about 492 nm, while 507 nm is clearly in the green section.

- The Wikipedia article "Visible spectrum" has a chart showing blue at 450-495 nm, and green at 495-570.

For these three references, 507 is within the green region and is not "on the border" at around 490 or 495.

A few years ago, I did a website which included laser wavelength tables. I used an online wavelength-to-RGB conversion calculator so that the on-screen colors for visible lasers would match (within obvious limits of equipment, calibration, etc.) the laser wavelengths. The resulting table is at http://www.lexellaser.com/techinfo_wavelengths.htm. Note that Argon at 501.7 nm is clearly green, not blue-green such as argon 496 or 488. This would mean that 507 nm would be even closer to a "pure" green.

(Unfortunately, I cannot now find the online wavelength-to-RGB calculator that I used at the time. I did find related sources, which include http://www.philiplaven.com/p19.html and http://www.midnightkite.com/color.html. Note at the latter the spectrums which use a wavelength-to-RGB conversion algorithm. On this spectrum, 507 is green -- I would not characterize it as "blue-green".)

For these reasons, I feel it is most correct to simply call 507 nm light "green". While it is towards the blue end of the "green zone" of the spectrum, it definitely is NOT an even mix of blue and green (e.g., cyan). Based on the sources above and especially the wavelength-to-RGB conversion, I feel most people seeing 507 nm light would call it "green". More specifically, if asked to compare 507 nm light with a pure blue (around 470), a blue-green (around 490-495), and a pure green (around 530), I feel most people would say that 507 nm would be closest to green, not to blue-green.

Pmurph5 03:44, 13 August 2007 (UTC)

This is highly subjective, but both based on the wavelength diagram Image:Spectrum441pxWithnm.png and Image:CIExy1931.png and my personal experience with tunable lasers I would call the range 480-510 nm "blue-green". So I disagree with you. But it wouldn't hurt to mention absolute wavelengths rather than subjective colors on the page. The peak of the night-vision sensitivity is much less relevant than the range, which I would call 450-550 nm, which is "blue and green". Han-Kwang (T) 07:08, 13 August 2007 (UTC)

Thanks for the comments. I did some more research, including speaking with one of the members of the SAE-G10T laser hazards subcommittee. Greg Makhov of Lighting Systems Design Inc. in Orlando helped SAE-G10T develop laser safety regulations for the U.S. FAA. Greg stated that the relevant parameter is photopic vision, not scotopic as I had mistakenly written in my original Wikipedia entry.

The reason is that pilots and others who might see nightime lasers almost always have some photopic vision. As Greg said: "If you can see colors, then your photopic vision is working." In a cockpit, this is almost always the case (e.g., control screens, etc.). True scotopic vision takes a long time to develop (dark adapt), and has no color perception.

The question of whether pilots see lasers photopically or scotopically was debated by the SAE-G10 committee members. They even considered alternatives such as a mix (mesoptic), or using the union of the scotopic and photopic curves (making a "top hat" curve). The final decision for using photopic data was primarily due to the fact that most pilots were in a bright enough environment that they had color vision (meaning cones, meaning photopic.)

As a result, the FAA's official Visual Correction Factor for lasers also uses a photopic curve. This can be seen in FAA Advisory Circular 70-1, which has forms to be filled out by those using lasers in airspace. Table 5 of AC-70-1 lists wavelength correction factors taken from the CIE normalized efficiency photopic visual function curve for a standard observer.

So, after doing this research, I have changed the Wikipedia entry appropriately. Thanks again for raising this issue which prompted me to look into it further.

Pmurph5 01:49, 15 August 2007 (UTC)

[edit] "Demonstration"

Underneath "Accidental vs. deliberate exposure", there is a sentence which says "(To demonstrate this, aim a laser pointer at a retroreflective street sign a block or two away.)". It may be a good idea to revise this as it may serve to encourage others to point laser pointers (most likely deliberately) out in the public, in addition to surprising others who happen to be witness to such a demonstration. —Preceding unsigned comment added by Saphius (talk • contribs) 04:19, 2 October 2007 (UTC)

Good point. I have taken the simple solution by removing the suggestion. It was not particularly encyclopedic in any case. Pzavon 01:55, 3 October 2007 (UTC)

[edit] How to add photo of laser guide star

This article previously had a photo of a laser guide star. Someone removed it, but I am unclear as to the reason. (The reason cited was that the photo appears in Wikimedia Commons, but I don't think this is true. The removed photo is NOT in Wikimedia Commons.)

Is it possible to use another photo of a laser guide star? There is one in Wikimedia Commons at http://commons.wikimedia.org/wiki/Image:Keck_laser_at_night.png. I don't want to add this willy-nilly without understanding 1) if this is OK and 2) the best way to do this.

Any help from more experienced Wikipedians is appreciated. If you could just put the cited photo in, that would be great. —Preceding unsigned comment added by Pmurph5 (talk • contribs) 23:31, 13 January 2008 (UTC)