Flash Blinded By Green Laser

The only "bizarre" aspect of this thread is the strained and strange
logic used by some of the participants. Your comparison between a green
pointer and a large bore sniper rifle is the latest twist. Why not a 155
howitzer?


Hi:

Why? Because you can trot down to the local gun dealer and buy a sniper rifle.
You cannot buy a howitzer. I can't anyway. ;-)

"People wouldn't shoot a firearm at an aircraft," you say? You don't know many
pilots.

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

Mij Adyaw wrote:

It is surprising that there is not a problem with kids pointing the
rifles
at airliners.

Is that a serious statement? Think about it. A kid (or adult for that
matter) fires off several shots at an airliner. One, it is very
unlikely that anything will hit the plane, and Two, the noise is likely
to draw people over to see what the hell is going on, at least if done
from the back yard. With a laser, the beam is continuous (unlike a
rifle) so one just needs to wave it around aiming at the plane, and
there is a good chance you will hit it with the beam. Plus, you can do
this in complete silence, making it unlikely you'd draw attention to
yourself.

Mark

None. You can deliver the entire 5mW output of a laser into the eye and
there
will be no damage. Adding a telescope doesn't change that. Furthermore, I
don't
think the scenario of a laser making it down a telescope aperture and out
an
eyepiece is very realistic. This could only happen if the telescope was
in a
horizontal position with someone at the eyepiece. Combine the likelihood
of this
unusual position with someone hitting the scope with a laser at the same
time.
I'd be more worried about getting hit by lightning.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


"Tim Killian" wrote in message
...


I'm stunned at the hubris it takes to make a blanket statement like this.
Look at the studies and safety guidelines -- with minimal concentration, a
5 mW beam can produce significant vision impairment, even retinal damage.
Anything from an electronic failure in the regulator circuit, to an
unfortunate alignment of optics could cause that concentration. Such
injuries may be unlikely, but I simply don't understand the cavalier
attitude expressed, and the chances you're willing to take with other
people's vision.


Tim, Chris is correct. Fifteen minutes of exposure caused no damage in this
study:

http://archopht.ama-assn.org/cgi/con...rt/118/12/1686

Paul Gustafson

"Rod Mollise" wrote in message
...

Hi:

Why? Because you can trot down to the local gun dealer and buy a sniper
rifle.
You cannot buy a howitzer. I can't anyway. ;-)


Actually ya can.....

Check out Daves Old Western Scrounger sometime !








































--
Only A Gentleman Can Insult Me And A True Gentleman Never Will

From the same web site:
http://archopht.ama-assn.org/cgi/con...ct/117/11/1557

"Maculopathy From Handheld Diode Laser Pointer
An 11-year-old girl was referred to our practice with a 3-week history of
visual decrease in her right eye. She reported that, while on the school
bus, one of her classmates had attempted to determine whether a laser
pointer would cause pupillary constriction. During the episode she stared at
the activated laser pointer for several multisecond exposures with the right
eye. She immediately noted decreased vision and a central scotoma in the
affected eye.

Three weeks later the best-corrected visual acuity was 20/60 -2 OD and 20/25
+2 OS. Amsler grid in the right eye revealed a relative central scotoma
involving the center 2°. Anterior segment was normal in both eyes.
Ophthalmoscopy of the right eye disclosed pigmentary clumping in the central
fovea with loss of the central foveal reflex (Figure 1)."

Concern about Laser Pointers:
http://www.hc-sc.gc.ca/english/iyh/products/laser.html

"Flashblindness is temporary. Your vision returns to normal after a few
moments, and there are no long-term effects. However, a longer look can
cause serious damage to your eyes. It's worse if the laser beam is being
projected through a piece of optical equipment, such as a telescope or a
pair of binoculars. In these situations, the laser beam could actually burn
a tiny spot, or cut open a blood vessel, on the retina at the back of your
eye. In a worst-case scenario, you could go blind."

Health Concerns of Hand Held Laser Pointers:
http://www.bccdc.org/content.php?item=54

"A survey of laser pointers available for retail sale in BC's Lower Mainland
revealed that class 3a diode lasers, emitting mostly red light are being
sold. Because they are lasers, injury to the retina can occur for
individuals using optical aids (binoculars, telescopes). The natural "blink
aversion response" would be unlikely to provide adequate protection from eye
injury for intrabeam viewing of class 3a lasers through these devices."

The potential hazard of laser pointers - The Photobiology Unit, University
of Dundee, Ninewells Hospital & Medical School:

"We have examined 30 laser pointers that have been removed from the
possession of accused persons by police in Scotland. An analysis has shown
that 28 were Class 3B (European), with radiated power up to 9.3 mW. We have
reviewed the relevance of these findings and this shows that they are
potentially hazardous if viewed directly. Transient exposure is unlikely to
cause long-term damage but prolonged exposure may cause permanent retinal
injury. They may also cause dazzle, the consequences of which could be
serious."

Gary


"Paul Gustafson" wrote in message
news:Kl3Ed.1261$Wp.382@lakeread07...

None. You can deliver the entire 5mW output of a laser into the eye and
there
will be no damage. Adding a telescope doesn't change that. Furthermore,
I don't
think the scenario of a laser making it down a telescope aperture and
out an
eyepiece is very realistic. This could only happen if the telescope was
in a
horizontal position with someone at the eyepiece. Combine the likelihood
of this
unusual position with someone hitting the scope with a laser at the same
time.
I'd be more worried about getting hit by lightning.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


"Tim Killian" wrote in message
...


I'm stunned at the hubris it takes to make a blanket statement like this.
Look at the studies and safety guidelines -- with minimal concentration,
a 5 mW beam can produce significant vision impairment, even retinal
damage. Anything from an electronic failure in the regulator circuit, to
an unfortunate alignment of optics could cause that concentration. Such
injuries may be unlikely, but I simply don't understand the cavalier
attitude expressed, and the chances you're willing to take with other
people's vision.


Tim, Chris is correct. Fifteen minutes of exposure caused no damage in
this study:

http://archopht.ama-assn.org/cgi/con...rt/118/12/1686

Paul Gustafson

On Sun, 09 Jan 2005 15:43:55 GMT, "Gary Honis" wrote:

From the same web site:
http://archopht.ama-assn.org/cgi/con...ct/117/11/1557

"Maculopathy From Handheld Diode Laser Pointer...

Gary, you are entirely missing the point. Of course people with pre-existing
pathologies (as was probably the case here) can be injured by lasers. You can
construct all sorts of extreme cases to show where problems might occur. But the
real point is that these situations are extremely rare. In actual practice, it
is doubtful that anyone at a star party will ever suffer any kind of damage
because laser pointers are present. The world is full of things that can cause
harm, but we recognize that this is offset by a benefit. If you are truly
concerned about laser pointers being hazardous at star parties, you should also
be arguing against the use of any electrical equipment, tripods, counterweights,
bicycles and kites during the day. Any of these latter things are far more
likely to result in injuries to their users and to bystanders.


"Flashblindness is temporary. Your vision returns to normal after a few
moments, and there are no long-term effects. However, a longer look can
cause serious damage to your eyes. It's worse if the laser beam is being
projected through a piece of optical equipment, such as a telescope or a
pair of binoculars. In these situations, the laser beam could actually burn
a tiny spot, or cut open a blood vessel, on the retina at the back of your
eye. In a worst-case scenario, you could go blind."

This is simply incorrect. No optical system can ever result in more energy, or a
greater energy density, at the retina than shining the laser directly into the
eye. If you had a laser that was already dangerously bright, and shone it
several hundred meters such that it was no longer dangerous, a large aperture
could collect all the energy and get it back into a beam small enough to enter
the eye. But that assumes that the original laser was intrinsically bright
enough to cause damage, which is not going to be the case with a correctly
branded class 3a device.


Health Concerns of Hand Held Laser Pointers:
http://www.bccdc.org/content.php?item=54

This page is full of factual errors. One example:

"The brightness (radiant intensity divided by the area of the emitting surface)
of the light from these small lasers is greater than that of the sun, even at a
large distance."

Truth: a 5mW laser and the Sun both deliver the same energy to the eye. The
spectral characteristics of the Sun make it more damaging. Once the laser is
farther than about 10 meters away, its beam had diverged to larger than the dark
adapted pupil size, and the energy delivered to the eye decreases (with the
square of the distance).

If these guys can't even get the most basic facts correct, and don't understand
basic optics, it is hard to take them seriously. It sounds like the biggest
concern is people running around abusing class 3b lasers, which is another
matter altogether.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

I think you need to review your statement. With additional optics, it's
possible to focus a coherent wavefront down to a theoretical spot size
one wavelength in diameter. So even with imperfect optics, it's possible
to increase the energy density of a 5 mW pointer by several orders of
magnitude through reflection and/or refraction. Yes, the total energy
delivered can never be higher, but the effect is _very_ different at the
spot of incidence. Most children learn this the first time they play
with a magnifying glass on a sunny day.

BTW, I'm sure the schoolgirl with degraded vision due to classmates
playing with laser pointers is comforted to know that her plight was the
result of some unfortunate coincidences and highly improbable events.

Chris L Peterson wrote:

This is simply incorrect. No optical system can ever result in more energy, or a
greater energy density, at the retina than shining the laser directly into the
eye. If you had a laser that was already dangerously bright, and shone it
several hundred meters such that it was no longer dangerous, a large aperture
could collect all the energy and get it back into a beam small enough to enter
the eye. But that assumes that the original laser was intrinsically bright
enough to cause damage, which is not going to be the case with a correctly
branded class 3a device.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sun, 09 Jan 2005 10:39:47 -0700, Tim Killian wrote:

I think you need to review your statement. With additional optics, it's
possible to focus a coherent wavefront down to a theoretical spot size
one wavelength in diameter.

You'll never manage that in the eye because first the light travels through the
cornea and lens, where a good deal of aberration occurs. The actual spot size on
the retina is never going to get much smaller than it gets from the refraction
of the eye alone, and it wouldn't really matter anyway since you'd be down to
the size where at worst you might damage a single rod or cone. I believe the
article is equating looking at a laser with a telescope to looking at the Sun
with a telescope. In the latter case you dramatically increase the total energy
delivered to the retina, but not in the case of the laser.


BTW, I'm sure the schoolgirl with degraded vision due to classmates
playing with laser pointers is comforted to know that her plight was the
result of some unfortunate coincidences and highly improbable events.

Few people who experience an injury resulting from an improbable occurrence are
comforted by the statistics. But we don't go around prohibiting useful tools
because they occasionally result in injuries.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Paper ignites at a delivered energy density 10W/cm^2, so even you will
agree that at 1W/cm^2, some eye damage is _possible_. A 5 mW pointer
beam 1mm in diameter has an energy density of about .64 W/cm^2. As I
said earlier, imperfect optics can easily increase the energy density of
a pointer above 1W/cm^2 because they only have to shrink the beam by 25%!

These are not harmless toys.

Chris L Peterson wrote:

On Sun, 09 Jan 2005 10:39:47 -0700, Tim Killian wrote:


I think you need to review your statement. With additional optics, it's
possible to focus a coherent wavefront down to a theoretical spot size
one wavelength in diameter.


You'll never manage that in the eye because first the light travels through the
cornea and lens, where a good deal of aberration occurs. The actual spot size on
the retina is never going to get much smaller than it gets from the refraction
of the eye alone, and it wouldn't really matter anyway since you'd be down to
the size where at worst you might damage a single rod or cone. I believe the
article is equating looking at a laser with a telescope to looking at the Sun
with a telescope. In the latter case you dramatically increase the total energy
delivered to the retina, but not in the case of the laser.



BTW, I'm sure the schoolgirl with degraded vision due to classmates
playing with laser pointers is comforted to know that her plight was the
result of some unfortunate coincidences and highly improbable events.


Few people who experience an injury resulting from an improbable occurrence are
comforted by the statistics. But we don't go around prohibiting useful tools
because they occasionally result in injuries.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sun, 09 Jan 2005 11:09:34 -0700, Tim Killian wrote:

Paper ignites at a delivered energy density 10W/cm^2, so even you will
agree that at 1W/cm^2, some eye damage is _possible_. A 5 mW pointer
beam 1mm in diameter has an energy density of about .64 W/cm^2. As I
said earlier, imperfect optics can easily increase the energy density of
a pointer above 1W/cm^2 because they only have to shrink the beam by 25%!

You can have much higher energy densities at the retina if the spot size is
small because both the vitreous body and the retinal circulatory system
efficiently carry heat away. Thermal damage to the retina by a 5mW visible light
laser is impossible, pure and simple. The rare (and largely anectodal) reports
of injury from low power lasers are presumably associated with phototoxicity.


These are not harmless toys.

Who said they were? But they are far less dangerous than Super Soaker squirt
guns. There have been many reports of ocular damage from those (and they
actually _are_ marketed as toys!)

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com