So here’s this Staff Report on the relative hazards of laser pointers and I think to myself that this is right up my
alley, so I’d better go jump into the discussion and help
dispel any ignorance that might creep in and, lo, there is no comment thread yet. Well, the Report was fairly
thorough and free from errors so maybe nobody has
anything more to say.
Bah! I want this subject discussed, dammit! The first time
since Ed mis-edited The Great One’s column on package
recycling --making it ever so slightly dubious-- that I
have any expertise to contribute and nobody has even
opened a thread. I’ll just do it myself then…
There! I even figured out how to include a link to the
relevant Staff Report. (I’d have done the same for the
recycling column but the archive search function returned
an “internal error”. Something about “chunked content”.)
Well, the article forgot to mention the possibility of the owner of said laser getting pumelled by an angry mob of people annoyed with childish behavior. I absolutely HATE being in a movie and having some lord of the jack-asses beaming his little toy onto the screen. Show some consideration you moron.
(sorry for the slight hi-jack…but it had to be said)
Personally, I am extremely thankful that the general public thinks laser pointers are dangerous, because the Better Half was once able to use that factoid to remove from circulation a group of high school wrestlers who were in the bad habit of harassing parents dropping off Midget Wrestlers at practice. On this particular occasion they were shining a laser pointer at people driving up in their cars, and it took him about 2 minutes to have the coach explain to them that they were supposed to leave after practice, not hang around. Up till that point, the coach had been like, “Oh, well, they’re not hurting anything, HEY, GUYS, YOU KNOW YOU’RE SUPPOSED TO GO HOME AFTER PRACTICE [shrug]”.
BTW, Jamoross, you didn’t say what your expertise is, exactly? Manufacturer of laser pointers? Repair of same? Chairperson of appropriate Congressional Sub-Committee investigating inappropriate appropriation of funds for appropriately equipping Operation Desert Storm commandos for the invasion of Kuwaiti movie theaters?
Oh, I’m an optical systems engineer. I am also a
designated laser safety officer. Well, I was when
I was in the U.S. Here in Japan that kind of thing
is much less formalized and is basically voluntary.
It’s the same job, just without the fancy titles.
Anyway, I’m Senior Engineer in a laser applications
laboratory and factory. I also teach laser safety
and review machine designs to insure they have the
proper interlocks and other protections.
Now I am interested, Jamoross, and seriously curious. Here’s my chance to “Ask the Expert”. Is it true that checkout clerks have to be very careful not to look down into the scanner when they beep things? I’ve never been a checkout clerk, but I think it would drive me crazy to be told “Don’t look at the red light, don’t look at the red light”. Are there documented cases where checkout clerks have been injured by looking at the red light?
You teach Laser Safety? Do you go around to Wal-Marts and hold meetings, or are you training the people who train the people? Or are we just talking industrial safety here?
It’s hard for me to visualize a laser pointer as an actual “laser”, as in “laser beam”, as in “Dr. Evil blowing up the world laser beam”. So the Staff Report is saying that the injury to the eye that results from having a laser pointer shined into it is simply the result of having a really bright light shined into it, the same as looking at the sun, and not from having a hole burned in the retina by a Dr. Evil-type laser beam? Well, there now, I didn’t know that.
Some of us are more tech-challenged than others. I just recently found out that cars don’t have carburetors anymore (they have fuel injection).
Laser pens are indeed banned in the UK. Whilst working at Gatwick Airport, London, I was instructed to confiscate said items if found upon the personage of people travelling into or out of the UK - my undesirable job at the time was to randomly search passengers and their luggage if flying with American carriers.
I think they were originally banned when they hit the headlines back in the mid 90’s. Kids were hanging out on motorway bridges, aiming them at passing drivers, causing all kinds of fatalities apparently…
Washington state passed legislation last year, making certain uses of laser pointers a crime.
Personally, I think it’s cool to realize we now have a law called UNLAWFUL DISCHARGE OF A LASER. Doesn’t that sound amazingly futuristic, like something from a 1950’s science fiction magazine?
I just spent about a minute shining a laser pointer into the eyes of a fly. Range was about 3 inches.I can now put my finger about 1/2 inch from the flys head and it just turns away. It must not be blind but 1/2 inch is pretty close.Kind of unscientific but I think I affected it’s sight. Don’t know if it is permanent or not.
The warning to checkout clerks stems from the power of
the lasers typically used in package scanners. There is
no real danger from a supermarket scanner so long as the
beam keeps moving. The “eyesafe” limits vary depending
on the wavelength (color) of the beam and whether or not
it is scanned. If the scanner happens to stop spinning
there is a good chance the operator will look down to see
what’s wrong. Personally, I doubt the admonition not to
look into the beam would overcome this natural tendency.
Keeping this in mind, part of the requirements for such
systems is a mechanism to interrupt the beam if the scanner
stops. But of course these thing can fail too, often in a
way that goes unnoticed until the unit actually stops
counting beer cans or whatever.
Listen Ducky, those nifty supermarket scanners are
“industrial” in more than one sense. Not that they are
especially dangerous, but they do have to be pretty tough
to withstand constant banging with 2-liter bottles and
the odd frozen turkey etc.
I have never personally taught in a Wal Mart store. Mostly
I teach repairmen, operators, and the engineers who design
and build systems that incorporate lasers.
Ahem. Stare at the Sun and you will burn a hole in
your retina. Imagine some miscreant holding a magnifying
glass between the Sun and a hapless ant. What happens to
the ant? Now remember that the lens of your eye is at
exactly the right distance from your retina to focus light
on it. Point your personal optic imagers at Old Sol and
your fovea will suffer the ant’s fate.
Lasers are more dangerous than a bright light because their
brightness doesn’t diminish with distance the same way
ordinary light does. If someone needs their vision to
survive, like the pilot of a helicopter or even a driver on
the highway, then even momentarily dazzling them can be
extremely dangerous.
Finally, permanent eye damage with even a strong pointer
(500 milliwatts or so) is very unlikely because of the
natural blink reaction. Anybody with a reaction time
longer than the quarter second mentioned in the Report has
a serious attention disorder anyway and was probably
pointing the thing at themselves.
Now, let no one think I am condoning staring at the sun,
but this analogy is a little off. I don’t mean to nit-pick,
but if we didn’t, what would the point of the message
boards be? And how can we let the optical engineer spread
inaccuracies about optics?
When one fries an ant with a magnifying glass, you attempt
to get the subject in the focal point of the magnifying
glass. Now, the lens of the eye projects an image on the
back of the eye. This image will always be behind the
focal point. As anyone who has ever tried to sizzle ants
knows, if you pull the glass back from where you get a
nice tight point (the focal distance) there is another
point where you will get a nice sharp image of the sky
projected on the area around your victim, er, subject.
And the cooking power of this image is not nearly as good,
but not bad either. That is how your eye works. If our
lens actually focused the light on the back of our eye
we’d all see one bright spot in the center of our field
of view. Although we’d be much better at seeing in the
dark, who cares when your vision is 10^38/20.
Try that experiment again, cjclark. The sky is far enough away to be considered infinitely distant, so the image distance is exactly equal to the focal distance. The light from any given point in the scene you’re viewing is focused onto a single point on your retina: The reason that you still see a complete scene is that you’re seeng many points, each focused in a different place. The spot of light you project onto the ant won’t quite be a point, because the Sun isn’t a point of light in the sky: It’s size will be equal to the sin(30’)*f, 30’ being the angular size of the Sun in the sky, and f being the focal length of the lens. With a single lens, you can’t get it to a single point no matter what you can do, all you can do is get the spot as small as possible, which is exactly the spot where you get a clear image of the Sun.
Except that in a 1950s story the author would probably have predicted that laws against lasers would be passed in 1970 or 1980. We are woefully lagging behind the predictions of early SF authors! Instead of sounding futuristic, it sounds quaint and outdated. In the year 2000, we should be outlawing teleportation of fraternity boys into the high school girls’ locker room.
I think the “nice sharp image of the sky” cjclark is
talking about is more likely an image of some nearby
objects like leaves on a tree or the silhouette of a phone
pole. These things are, um, substantially closer that the
Sun. Close enough in fact to require a very noticable
repositioning of a simple lens to image them instead of
the Sun behind them. At such a position the Sun’s image
would be slightly defocused and less intense.
Actually, no sequence of lenses will yield a single point
of light either. And there is another way to calculate the
size of the spot you will get with a simple lens. Just
multiply the diameter of the Sun by the focal length of
your lens and divide by 1 AU. This ignores lens distortion
(as does Chronos’ method) but will be very accurate.
Speaking of distortion, lens abberations are the bane of
insecticidal pyrolyzers everywhere. For a really hot spot,
you want a big lens with a short focal length. This would
mean a pretty globular piece of glass with consequently
lots of spheric distortion.
Unless you use a Fresnel lens.
These are usually flat plastic lenses like you sometimes
see stuck on the back window of motor homes. For a few
bucks you can get some nice big ones from Edmund that
are plenty dangerous in sunlight. Forget the ants; you can
burn holes in the asphalt with one of these babies.
[hijack]
:eek: Arnold, this is scary–only this morning I received an e-mail from a friend, warning me about THIS VERY THING!! Yes, it seems that fraternity boys at Northwestern in Evanston are using equipment from the National Accelerator Laboratory to beam themselves into the girls’ locker room at Sacred Heart High School in Naperville. Parents are furious, and are calling for legislation to outlaw this.
Please, please, contact your members of Congress, and forward this e-mail to everyone you know.
[/hijack]
We now return you to your regularly scheduled Real World.
"EVANSTON- In a bizarre demonstration of collegiate
ingenunity, several students from the McCormick School
of Engineering and Applied Science at local Northwestern
University allegedly invaded a high-energy laser facility
at the Fermi National Accelerator Laboratory in nearby
Bativia over the weekend. The boys turned the lasers on
themselves in what was initially thought to be a desperate
escape attempt. Investigators now believe that the boys
had purposefully planned the entire incident to ‘beam’
themselves to a high school in Wheaton five miles away.
"Powerful light beams were used to separate and analyze
the atomic structure of their bodies. Laboratory Director
Michael S. Witherell explains: ‘The three young men were
disintegrated and at first we thought they had died, you
know, like ants under a really big magnifying glass. Then
a researcher noticed that one of our particle accelerators
had also been tampered with and was still active. That’s
when we decided they may have actually escaped.’
"But that wasn’t the whole story. Their destination was
St. Francis High School on Roosevelt Road in Wheaton
where a girl’s basketball tournament was in progress.
Amidst dozens of girls in various states of undress, the
boys materialized near the shower area in the girl’s locker
room. According to a coach of one of the visiting teams,
many girls were startled or became upset but none of them
realized how the invaders had accomplished their entry.
‘I thought they just sneaked in or had been hiding’ said
one girl whose name was not released. Said another,
‘Somebody yelled so I looked around and they were right
there’.
“An individual claiming to be a friend of the boys and
asking that his name be withheld said the whole idea came
about while playing with a handheld laser pointer more than
two years ago. The pointers have recently been banned from
area high schools.”
