 | | From: | anton jopko | | Subject: | why are lasers dangerous to eye | | Date: | Fri, 14 Jan 2005 08:16:50 -0500 |
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 | Dear Group,
Why are lasers dangerous to the eye. Their power is only 5 mw whereas a
flashlight shining into the eyes would be thousands of times brighter yet no
one claims flashlights are dangerous to the eyes?
Your thoughts welcomed,
anton
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| | From: | Don Klipstein | | Subject: | Re: why are lasers dangerous to eye | | Date: | Fri, 14 Jan 2005 14:45:46 +0000 (UTC) |
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| In article , anton jopko wrote:
>Dear Group,
>Why are lasers dangerous to the eye. Their power is only 5 mw whereas a
>flashlight shining into the eyes would be thousands of times brighter yet no
>one claims flashlights are dangerous to the eyes?
1. A typical 3-D-cell Mag Light may produce about half a watt of
radiation of wavelengths that can reach the retina - but what percentage
would get through your pupil?
2. Once it does get through, it is spread out over a much larger area of
the retina than the tiny point that a laser beam would be focused onto.
3. I figure that Mag Lights and many other flashlights are not so
perfectly safe to stare into for more than several seconds to a minute or
two anyway. (One exposure limit that has regulatory force for laser
products in the USA is 20 joules per steradian in any 10,000 second period
for wavelengths 400-1500 nm, if I remember it correctly. As for steradian
of what - I believe source apparent angular area or retina angular area.)
- Don Klipstein (don@misty.com)
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| | From: | Don Klipstein | | Subject: | Re: why are lasers dangerous to eye | | Date: | Sat, 15 Jan 2005 05:19:48 +0000 (UTC) |
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| In , I, Don Klipstein wrote in part:
>
>3. I figure that Mag Lights and many other flashlights are not so
>perfectly safe to stare into for more than several seconds to a minute or
>two anyway. (One exposure limit that has regulatory force for laser
>products in the USA is 20 joules per steradian in any 10,000 second period
>for wavelengths 400-1500 nm, if I remember it correctly. As for steradian
>of what - I believe source apparent angular area or retina angular area.)
I am not a morning person.
I now remember the exposure limit for a non-point source being 20 joules
per square centimeter per steradian within a 10,000 second period for
wavelengths 400-1500 nm. (Excluding situations where pulses are short and
intense enough to require a lower limit.)
It appears to me this means 20 joules per square centimeter of front
surface of eye per steradian of angular source area (or angular image area
of the retina).
I hope I got that right - otherwise please say so!
- Don Klipstein (don@misty.com)
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| | From: | Al | | Subject: | Re: why are lasers dangerous to eye | | Date: | Sat, 15 Jan 2005 17:33:50 GMT |
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| In article ,
don@manx.misty.com (Don Klipstein) wrote:
> In , I, Don Klipstein wrote in part:
> >
> >3. I figure that Mag Lights and many other flashlights are not so
> >perfectly safe to stare into for more than several seconds to a minute or
> >two anyway. (One exposure limit that has regulatory force for laser
> >products in the USA is 20 joules per steradian in any 10,000 second period
> >for wavelengths 400-1500 nm, if I remember it correctly. As for steradian
> >of what - I believe source apparent angular area or retina angular area.)
>
> I am not a morning person.
>
> I now remember the exposure limit for a non-point source being 20 joules
> per square centimeter per steradian within a 10,000 second period for
> wavelengths 400-1500 nm. (Excluding situations where pulses are short and
> intense enough to require a lower limit.)
> It appears to me this means 20 joules per square centimeter of front
> surface of eye per steradian of angular source area (or angular image area
> of the retina).
> I hope I got that right - otherwise please say so!
>
> - Don Klipstein (don@misty.com)
What is the exposure from those very annoying zenon auto lights? Boy do
I hate them. They blind me when they approach. Am I the only one that
feels this way? In my opinion, they should be banned.
Al
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| | From: | Skywise | | Subject: | Re: why are lasers dangerous to eye | | Date: | Sat, 15 Jan 2005 20:41:44 -0000 |
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| Al wrote in
news:no.spam-DC3494.12335215012005@news.verizon.net:
> What is the exposure from those very annoying zenon auto lights? Boy do
> I hate them. They blind me when they approach. Am I the only one that
> feels this way? In my opinion, they should be banned.
>
> Al
It may be that they are running in high beam mode or their lights
are not adjusted properly. These lights have baffles to keep the
light at or below level with the headlamp when properly adjusted.
These HID lights are 'whiter' than normal incandescent lamps. This
has the affect of making them appear blue. You know how many quality
digital camera's allow you to adjust the whit balance of the image?
Well, the human eye does the same thing. Your eyes adjust to the
amber color of street lighting and the yellow color of car headlights
making white lights appear blue. If ever car had HID lights, you
likely would see an old car with incandescent lights as appearing
orange.
Some other considerations...
A dirty windshield (inside and out) can contribute greatly to glare
from any light source at night.
Don't stare at the oncoming lights. You're not a deer.
BTW, it's xenon, not "zenon."
Brian
--
http://www.skywise711.com - Lasers, Seismology, Astronomy
Sed quis custodiet ipsos Custodes?
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| | From: | John Savard | | Subject: | Re: why are lasers dangerous to eye | | Date: | Mon, 17 Jan 2005 00:24:02 GMT |
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| On Fri, 14 Jan 2005 08:16:50 -0500, "anton jopko"
wrote, in part:
>Why are lasers dangerous to the eye. Their power is only 5 mw whereas a
>flashlight shining into the eyes would be thousands of times brighter yet no
>one claims flashlights are dangerous to the eyes?
A laser produces a beam of coherent light. That is light which comes
from a perfect point source, and which can be focused to a very tiny
spot on the retina. Tiny enough that the energy density within that spot
can burn and cut things.
John Savard
http://home.ecn.ab.ca/~jsavard/index.html
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| | From: | L. Michael Roberts | | Subject: | Re: why are lasers dangerous to eye | | Date: | Fri, 14 Jan 2005 10:06:51 -0500 |
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| anton jopko wrote:
> Dear Group,
> Why are lasers dangerous to the eye. Their power is only 5 mw whereas a
> flashlight shining into the eyes would be thousands of times brighter yet no
> one claims flashlights are dangerous to the eyes?
> Your thoughts welcomed,
> anton
See: http://www.laserfx.com/BasicSafety/BasicSafety2.html
--
+==================== L. Michael Roberts ======================+
This represents my personal opinion and NOT Company policy
Goderich, Ont, Canada. To reply, post a request for my valid E-mail
"Life is a ually transmitted, terminal, condition"
+================================================================+
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| | From: | Sam Goldwasser | | Subject: | Re: why are lasers dangerous to eye | | Date: | 14 Jan 2005 08:50:55 -0500 |
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| "anton jopko" writes:
> Why are lasers dangerous to the eye. Their power is only 5 mw whereas a
> flashlight shining into the eyes would be thousands of times brighter yet no
> one claims flashlights are dangerous to the eyes?
The quick answer is that it's because the beam from a typical laser can
focus to a much smaller spot on the retina than most "normal" light sources.
But note that the amount of power getting into the eye from looking directly
at the Sun is the same order of magnitude and that, too, can result in
vision damage.
Much more info at any laser safety Web site (Google: laser safety), and in
the Laser FAQ:
http://repairfaq.ece.drexel.edu/sam/lasersaf.htm
--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
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