Flash Blinded By Green Laser

In article , Brian Tung wrote:
Tim Killian wrote:
Your "experiment" proves that uninformed people are dangerous to
themselves and others. You should not own even that 5 mW laser!

The retina of the eye cannot feel pain. Just because you decided to try
and destroy a portion of it doesn't mean that green lasers are eyesafe.
I hope you tried this stunt in private where no one else could witness
your stupidity.

Let's put aside for the moment whether Stuart should have performed the
experiment, or whether he is really uninformed--which, after all, you
don't really know.

If the claim is that a pilot was flash blinded at thousands of meters,
then Stuart's inability to flash blind himself at less than a meter is
entirely relevant and establishes the case that it can't have happened--
at least not in the way described. I hope that Stuart hasn't damaged
his retina indetectably, but even if he has, that wasn't the nature of
the claim.

Well -- I wouldn't quite say that my test established that.
I feel safe in saying that a brief direct exposure didn't do me any
long-term harm, but "flash-blinding" doesn't sound long-term either.
What I experienced probably qualifies as flash-blinding. It faded in
a minute or so.

Of course, I agree that it'd take a lot more power to annoy a pilot
thousands of feet away. But then a pilot needs to be paying close
attention when landing, and surprises might be dangerous
even if they're well below the threshold of flash-blinding.

In that way, of course, publicizing a potential "terrorist threat"
may make misguided laser hobbyist jerks *more* dangerous,
if a pilot interprets a brilliant green glare as an attack.
Can't win I guess.

Hi Alan,

I agree that putting a green laser pointer in the same category as an
unshielded all-night security light is pretty silly. That was not my
statement. I did give one reason that astronomers should strongly
discourage their use (green lasers), "because they are another form of
light pollution".

Let me explain why I feel this way. I think the green laser accident
motivated me in the same manner as someone whose neighbor installed a bad
light (light trespass). It was an upsetting experience for me. My eyesight
is very important to me. The last thing I want to be worried about at a
star party is being hit in the eye with a green laser again.

Star Parties: Good dark sky sites are getting harder to find. In PA, we
are fortunate to have a dark sky site (Cherry Springs Dark Sky Park) about
as far from light pollution as you can get in the East. In recent years,
amateur astronomers have been showing up with green lasers, shining bright
spots on tents and wiggly lines onto the tree line of the observing field.
This is a light pollution problem to those that are doing astrophotography,
astro-imaging or trying to stay dark-adapted. Astrophotographers have had
their long exposure photographs ruined by green lasers. Many would respond:
Why are you trying to do astrophotography, astro-imaging or serious deep sky
observing at a star party? To me, that is very sad. If not in a protected
Dark Sky Park, then where?

Our dark sky observing sites in the East are becoming few and very crowded.
Like thirsty animals fighting over the last ponds of water in desert
wasteland, amateur astronomers are loosing the natural night sky. Our club
astronomy presentations at star parties for the public always include a
discussion of "light pollution" and keeping unnecessary light from shining
into the night sky. How can you follow that with shining a green laser beam
(or mag light) into the sky to point out stars? What kind of example does
that set? How many children will ask their parents for a "green light
saber" versus a new telescope after the laser show?

For 15 years our club has been active in getting light pollution ordinances
adopted locally with good success. The ordinances we recommend contain the
requirement: "The use of searchlights or laser source lights for advertising
or entertainment purposes is prohibited." How can we ask businesses to not
direct lasers (and searchlights) into the night sky for their commercial
benefit, and at the same time do the same because it is in our interest?
Using a green laser light beam to point out objects in the night sky is very
easy and effective. Is it the only way? Not using a green laser as a
pointing device takes more effort; but it has been done and continues to be
done by many astronomy clubs, to teach the public about the wonders of a
natural night sky, not the awesome power of a laser light saber.

I'm sure that your constellation tours with the geen laser pointer are well
received. Star party organizers are faced with the possibility of laser
misuse and accidents and liability concerns. I have been using a red
filtered notebook display in a shrouded "Dewbox" for constellation tours at
star parties and it works very well using "The Sky" software. Being able to
click on a deep sky object to display an image is also very useful to give
an idea of the view at the eyepiece.

Dark skies,

Gary



"Alan French" wrote in message
.. .

"Gary Honis" wrote in message
...
[SNIP] I have also been
a very active dark sky advocate for many years and I feel that
astronomers
should strongly discourage their use for the following reasons:
[SNIP]
They are another form of light pollution.

Their use is unnecessary.

Gary,

I own a green laser pointer. While the use of one may be unnecessary, I
find it a very, very useful tool for doing constellation tours. I used to
use Maglights, which produced a much more annoying light beam and did not
work as well. I certainly am careful about where I use mine, and would
not,
for instance, take one to Texas Star Party. There is certainly a long
list
of modern conveniences youo could claim are "unnecessary."

I would disagree that a laser pointer is light pollution. The light all
goes where it does the work needed, and it is only on while it is being
used. To put a green laser pointer in the same category as an unshielded
all-night security light is pretty silly.

I do find that there is a disturbing number of folks that consider these
toys - they should not be used for entertainment on cloudy nights. I
almost
got one in the face at WSP a few years ago - it just cleared my head. I
fear that their misuse may make things more difficult for folks who use
them
responsibly

Clear skies, Alan

Gary,

After trying to wade through this lengthy thread, it still was unclear
to me whether your vision returned to normal after this unfortunate
accident? I wanted to wish you the best and hope that your vision
eventually returned to normal. That this occurred from a low-power red
laser in an ubiquitious laser collminator inadvertently hitting a
parabolic telescope mirror is cause for concern. Your experience is a
fair warning as to the level of reasonable care needed to be taken by
all of us when attending star parties. - Canopus56

P.S. - Has anyone worked out a table based on the physics of this, i.e.
- the "safe" distance for a _red laser_ inadvertently hitting various
aperature sizes?

canopus56 wrote:

Gary,

After trying to wade through this lengthy thread, it still was unclear
to me whether your vision returned to normal after this unfortunate
accident? I wanted to wish you the best and hope that your vision
eventually returned to normal. That this occurred from a low-power red
laser in an ubiquitious laser collminator inadvertently hitting a
parabolic telescope mirror is cause for concern. Your experience is a
fair warning as to the level of reasonable care needed to be taken by
all of us when attending star parties. - Canopus56

P.S. - Has anyone worked out a table based on the physics of this, i.e.
- the "safe" distance for a _red laser_ inadvertently hitting various
aperature sizes?

Check out the following URL:
http://www.fas.org/man/dod-101/sys/s...l-hdbk-828.htm

Dave Nagel

I don't know how pilots are being flash blinded.that's is what the FBI is
trying to figure out.

HI:

And I expect they'll have a difficult time doing so. ;-)

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

On Fri, 31 Dec 2004 19:41:38 -0600, "David G. Nagel"
wrote:

canopus56 wrote:

Gary,

After trying to wade through this lengthy thread, it still was unclear
to me whether your vision returned to normal after this unfortunate
accident? I wanted to wish you the best and hope that your vision
eventually returned to normal. That this occurred from a low-power red
laser in an ubiquitious laser collminator inadvertently hitting a
parabolic telescope mirror is cause for concern. Your experience is a
fair warning as to the level of reasonable care needed to be taken by
all of us when attending star parties. - Canopus56

P.S. - Has anyone worked out a table based on the physics of this, i.e.
- the "safe" distance for a _red laser_ inadvertently hitting various
aperature sizes?

Check out the following URL:
http://www.fas.org/man/dod-101/sys/s...l-hdbk-828.htm

Dave Nagel

Hey! These sound like fun:

30.3 Ruby LRFs.

The ruby LRFs on the tanks are the most hazardous lasers to the eye at
close range. These lasers not only pose a hazard while viewing the
laser from within the direct beam, but also from viewing the diffusely
reflected laser radiation. The distance "t" is the distance from the
laser within the laser beam path in which there is both a skin hazard
and diffuse reflection hazard. Distance "t" represents the range to be
cleared in front of the tank.

I dissent from the analogical argument. Cars and trucks are essential to
the functioning of our modern economic system, hence we tolerate the
level of accidents that go with them while trying to lessen this level
by education.
Green laser pointers are not essential to the functioning of dark sky
star parties; indeed they are an aesthetic nuisance and impede our
appreciation of a true dark sky. No one wants to drive several hours to
a dark sky to see green lasers. For this reason they should be banned,
and star parties are now banning them.
A second reason for banning them at star parties is that there is a
danger of accidentally having one shone in one's eye, not necessarily
by a stupid or irresponsible person but even accidentally by a
knowlegeble and responsible person, as in the incident described by the
original poster in this thread. I don't want to get hit in the eye by
one and so I favor banning.
Shingletown and RTMC both ban them, wisely I believe, for both of
these reasons.
I think a public educator at a publicly attended local star party could
use one, just one, laser as a very effective teaching tool, as Rod
Mollise who does such teaching, and several others, who use them in
teacing, have pointed out. But this is one educator using one laser at a
public star fest in non true dark conditions.
I use a green laser finder when obsering alone, and I mean alone, and
to me it is the best telescopic finder I have ever used. I used to use
it all night when observing alone, but now I just use it to align on the
two stars for my Sky Commander digital setting circles.
Clear skies,
Bill Meyers



shneor wrote:
I would venture to say that automobiles kill more people every day in
the US than willl ever be hurt by green lasers in the course of 10
years. I don't see anyuone calling for banning cars. Instead, we enact
laws and rules to govern the use of cars. It's the same with green
lasers. Exercise appropriate care in their use and storage to eliminate
the possibility of accidental damage. IMO, it's absurd to ban green
lasers at star parties. Maybe we do need a 10-minute class on their
safe use.

Clear skies,
Shneor Sherman

Hi, Alan,
I respect your judgment and I think it is fine that use usa a green
laser pointer in teaching. One green laser, used by you alone, in
teaching at a local star party, not a true dark star party to which
people travel hours or days.

What is most striking in you post and most important is that you
narrowly escaped getting a green laser beam shone into you eye at a star
party. Your narrow escape that you underwent, is a clear confirmation
that what happened to the original poster can and will recur at other
star parties. And that is the basic issue of this thread for amateur
astronomers, not planes or cars or guns.
Green laser pointers are an aesthetic nuisance and an eye danger at true
dark star paries.
Best regards,
Bill Meyers

Alan French wrote:

"Gary Honis" wrote in message
...

[SNIP] I have also been
a very active dark sky advocate for many years and I feel that astronomers
should strongly discourage their use for the following reasons:
[SNIP]
They are another form of light pollution.

Their use is unnecessary.


Gary,

I own a green laser pointer. While the use of one may be unnecessary, I
find it a very, very useful tool for doing constellation tours. I used to
use Maglights, which produced a much more annoying light beam and did not
work as well. I certainly am careful about where I use mine, and would not,
for instance, take one to Texas Star Party. There is certainly a long list
of modern conveniences youo could claim are "unnecessary."

I would disagree that a laser pointer is light pollution. The light all
goes where it does the work needed, and it is only on while it is being
used. To put a green laser pointer in the same category as an unshielded
all-night security light is pretty silly.

I do find that there is a disturbing number of folks that consider these
toys - they should not be used for entertainment on cloudy nights. I almost
got one in the face at WSP a few years ago - it just cleared my head. I
fear that their misuse may make things more difficult for folks who use them
responsibly

Clear skies, Alan

Hello, Jon,
Your experience is yet another indication, besides those of Gary Honix
and Alan French, indicates that accidentally getting a laser beam in
one's eye is a predictable event at star parties where they are
allowed, unless these are banned at star parties except for the lecturer.
Glad you are okay,
Bill Meyers

Jax wrote:

wrote in message
oups.com...


I'm sorry to report that the accident referred to did occur, and
although it was an accident, I was responsible for it. It was not a
green pointer, but a collimator.


Thanks for your quick response, Howie. I have been accidently hit in my
dark adapted eye with a green laser pointer of yours from 20' away with no
impact other than it was annoying. Is the collimator more a risk than the
pointer?

Peace,
Jon

Brian Tung wrote:

For what it's worth, typical divergence for a GLP is 1 milliradian. That
is 1 mm of divergence per meter of traversal. By the time the beam has
travelled even a kilometer, it has diverged 1 meter.

The last one I had chance to play with was a bit better than that -
about 0.2 milliradian or roughly 2cm divergence in 100m. That makes the
spot size at distance 5x smaller and the energy density 25x more.

is at most 1/140 as wide, the intensity entering your eye is at worst
140^2 or 20,000 times smaller than it is point blank. You might as well
be shining a 250 nanowatt laser directly into your eye.

Or 6uW if a better specimen is used. But still low enough power to be at
worst an annoying distraction.

typical cruising altitude), the intensity is down a further factor of 100.
That is 2.5 nanowatts. When you consider that a pilot rarely looks
straight down from 10 km, the power probably drops down to something in
the neighborhood of 1 nanowatt.

And that is straight up. I'd guess that to be in a commercial airline
pilots cockpit view in level flight the source would need to be some
distance away from the plane horizontally too (worth another factor of
2? decrease in effective power density?).

I can see how they could be a real nuisance for night flights on final
approach, but not how they can threaten a cruising aircraft at 10000+
feet. Homeland insecurity seems to be in paranoid mode again.

Regards,
Martin Brown