My Eyes! My Eyes!

[ElektroFreak]

FOR THOSE OF YOU WHO DO TRY, THANK YOU!! FOR THE REST OF YOU, JFC!, PLEASE MAKE A SERIOUS, PEER REVIEWED, FACT CHECKED, SAFETY STICKY!!


Steve

Created a thread. It's still a work in progress. Please check it over and let me know if you have any additions, Steve. Your input is vital.

Thanks!

 

[Ash]

there is no difference whatsoever on -how- that light enters your eye... directly from the laser, bouncing off a mirror, or a bright dot on the wall accross the room. It is the quantity that matters, not the delivery route.

I agree and disagree. It is the quantity that matters, but with different delivery routes (direct/ reflected/ diffuse) different quantities of laser light enter the eye.

From simple calculations and observation, I can clearly see that the density of a laser beam is reduced farther from the laser aperture.
Lets say at the focal point you have 100mW of 532nm light concentrated to a point that is 532nm (2.09 x 10^-5 inches) in diameter. This calculates to 4,784,688mW per inch [concentration]. Now, a laser that is reflected off a mirror at a distance from the aperture will have a less-concentrated dot (lets say: an inch in diameter) with the same amount of power (100mW). This calculates out to 100mW per inch [concentration]. The focused laser will do a great deal more damage to an eye than a laser that has been reflected off a mirror and has a sort of "diluted" concentration of photons. Finally, a laser-dot on a wall will do quite a bit less damage because the light entering your eye is extremely diffuse. But, even looking at a dot on a wall from a 100mW 532nm laser can do damage (whether you believe it or not).
Now, please don't get me wrong. I wholeheartedly endorse the use of safety goggles for anyone using a laser >10mW. But, IMO, if conditions are right, and all possible variables are accounted for, using a high-powered laser in some situations without safety goggles is (IMO) alright (albeit unwise).

 

[Benm]

@Steve:

I admire your enthousiasm about keeping things safe. You're clearly going for a zero-risk approach, which would be appropriate in situations where you expose another person to laser light.

When exposing yourself, however, i think people should have the best possible information to determine what the risk is, and base on that if they are willing to take it or not.

For the latter scenario it is still very useful to be able to do at least basic calculations, even if they contain a number of (reasonable) assumptions. Obviously a safety margin is required because of any assumptions, but i still firmly believe it is useful. These calculations can also aid in determining the danger from reflected light, such as when looking at a laser dot on a wall... and they will show that looking at a 500 mW green dot from 2 inches distance is probably a very bad idea. On the other hand, they will also show that shining that same laser directy into someones face from the moon poses no significant risk.

Mis-labeling by manufacturers is a very serious problem though, in freak cases lasers can put out 10 times the value on the label (5mW greens are notorious for that). If you don't know, you can use the amount of electrical power a laser uses as an upper limit. This is likely to grossly overestimate power output, but certain never to underestimate it.

 

[LSRFAQ]

If I had a easy way of doing the scattering coefs.. But I don't, and some materials are neither cosine nor lambertian, but a mix. That is the gotcha. How do you express to someone when scattering off say white paper is fine, and frosted glossy glass is not, if they are 2 cm, 20 cm, 200 cm away.

"If you don't know, its best not to do that" is the rule you default to..

How????? , when we write this thing (and I wont get to it till late this weekend)
Do We/I express diffuse reflection without measurements ????

Scattering is a whole book...

I moved to a new town after cutbacks at the old job and there is NOT a copy of Sliney here, I no longer have access to Scifinder, I cannot easily look it up...

Steve

 

[ElektroFreak]

I agree and disagree. It is the quantity that matters, but with different delivery routes (direct/ reflected/ diffuse) different quantities of laser light enter the eye.

From simple calculations and observation, I can clearly see that the density of a laser beam is reduced farther from the laser aperture.
Lets say at the focal point you have 100mW of 532nm light concentrated to a point that is 532nm (2.09 x 10^-5 inches) in diameter. This calculates to 4,784,688mW per inch [concentration]. Now, a laser that is reflected off a mirror at a distance from the aperture will have a less-concentrated dot (lets say: an inch in diameter) with the same amount of power (100mW). This calculates out to 100mW per inch [concentration]. The focused laser will do a great deal more damage to an eye than a laser that has been reflected off a mirror and has a sort of "diluted" concentration of photons. Finally, a laser-dot on a wall will do quite a bit less damage because the light entering your eye is extremely diffuse. But, even looking at a dot on a wall from a 100mW 532nm laser can do damage (whether you believe it or not).
Now, please don't get me wrong. I wholeheartedly endorse the use of safety goggles for anyone using a laser >10mW. But, IMO, if conditions are right, and all possible variables are accounted for, using a high-powered laser in some situations without safety goggles is (IMO) alright (albeit unwise).

You guys do understand that you're arguing laser safety with the guy who pretty much literally wrote the book on Ar/Kr lasers (much of the gas laser section of Sam's FAQ owes it's existence to Steve), right? He's also a paid professional in the field of optoelectronics. I'm going to go way out on a limb here and say that he's forgotten more about lasers than we'll ever know. I think he's just a TINY bit more "in the know" about these things than we are.

 

[LSRFAQ]

You guys do understand that you're arguing laser safety with the guy who pretty much literally wrote the book on Ar/Kr lasers (much of the gas laser section of Sam's FAQ owes it's existence to Steve), right? He's also a paid professional in the field of optoelectronics. I'm going to go way out on a limb here and say that he's forgotten more about lasers than we'll ever know. I think he's just a TINY bit more "in the know" about these things than we are.[/QUOTE]

Modesty mode on, I wrote PART of the book on hobby use and keeping them going If you don't have a manual...

Guys named Bridges, McMahan, LaBuda, Hobart, Mohler, well, the list is about 40+ names long, wrote the book on the invention, physics and design.

And truth be told, the argon chapter needs a good rewrite, based on what I know and have documentation for now, but guessed/measured then, plus the effects of editor diffusion..

Steve

 

[StardustSprinkles]

You have to remember, there is suck a thing as too safe... If we treated everything like y'all are suggesting we treat lasers, cars wouldn't go over 5mph and airsoft guns would be test fired from a bomb proof bunker...

 

[ElektroFreak]

Look, if you want to risk your sight, go ahead, but don't assume that it's OK to promote a careless attitude about laser safety based solely your ideas of "too much safety". You're not even remotely qualified to make such a statement, and doing so puts others at risk if they believe such nonsense.

We're not talking about cars and airsoft guns, we're talking about lasers. Lasers have been shown to be dangerous since they were invented. Immediately it was clear that care must be taken. The guys who make these guidelines are educated scientists who have written books on the subject of light and lasers, but we should all listen to woodofcville instead because we're being "too safe"? ROFL.

And it's not "US'ALL" that are suggesting this. IT'S JUST BLOODY COMMON SENSE!!!!!!!!!!!!!!!!!!!!!!

Seriously, is it that hard to get a set of goggles? Or would you rather have the risk of eye damage?

Yeah, less than $30 is MUCH too much to spend to reduce the risk of personal injury, right? Give me a break.

 

[StardustSprinkles]

Lol, way to insult me. Great one. I was simply making a comparison, if I were to bring up the numbers for car accident injuries, or injuries due to misuse of airsoft guns, I'm sure lasers would look very safe in comparison. My point here was, and still is, if some can't handle the choice to not misuse something, people will limit and limit it until it has been banned for all.

-thanks so much for the super-friendly enlightenment though EF. :beer: [/sarcasm]

 

[ElektroFreak]

Where did I insult you? Putting things in perspective isn't the same as insulting you... I'm sorry you took offense, but the fact remains you're unqualified to trivialize laser safety.

 

[Jaseth]

Woodofcville:
A car has seat belts. A car has air bags. A car is designed to get crushed easily to absorb force. A road has warning signs and speed restrictions.
Air soft guns are used with large amounts of protective gear and air soft games are only allowed in certified areas with many safety precautions, including goggles and masks, even for the weakest ones.

All you have to do to protect yourself from a laser is wear the appropriate goggles. Why is it so hard to follow safety advice?
​

 

[Traveller]

Wikipedia:
"A transient increase of only 10 °C can destroy retinal photoreceptors. If the laser is sufficiently powerful, permanent damage can occur within a fraction of a second, faster than the blink of an eye. Sufficiently powerful visible to near infrared laser radiation (400-1400 nm) will penetrate the eyeball and may cause heating of the retina..."

"The eye focuses visible and near-infrared light onto the retina. A laser beam can be focused to an intensity on the retina which may be up to 2×10E5 times higher than at the point where the laser beam enters the eye. Most of the light is absorbed by melanin pigments in the pigmentepithelium just behind the photoreceptors, and causes burns in the retina"

Class IIIb
Lasers in this class may cause damage if the beam enters the eye directly. This generally applies to lasers powered from 5–500 mW. Lasers in this category can cause permanent eye damage with exposures of 1/100th of a second or less depending on the strength of the laser. A diffuse reflection is generally not hazardous but specular reflections can be just as dangerous as direct exposures.

...blink reflex is largely triggered by the apparent brightness of a light source... There are two mechanisms of pain from exposure to light: The primary one is optical overload ... The other mechanism of pain is actual thermal damage...

Ben, as correct and accurate as your definitions are, my main concern is the actual numbers in play.

The article I quoted states that permanent damage can occur with a >5mW laser in as little as 1/100s. Furthermore, the intensity of the light reaching the cornea is then "collimated" by the eye's lens by 2*10E5 the intensity when it finally reaches the retina, the human body's thinnest membrane.

Do we blink faster than that? I don't know, but I'd just assume not find out by trial & error :yh:


on the FLIP-SIDE...
I'm no expert (that would be Dad), but lasers play a vital role in posterior surgery by cauterizing blood vessels and sealing retinal tears. Ophthalmologists have worked with an array of lasers, including Argon (488 / 514 nm), Nd:YAG (1064 & 532nm... sound familiar ) as well as diode (810 nm). I think the very first surgical laser was ruby...

Thou giveth and thou taketh, oh great laser... :beer:



p.s. I think we scared the OP off... he may just be contemplating another hobby by now...

 

[Deleted member 8382]

@jaseth: because a decent goggles won't let you see a shit from your 15mW projector and the risk IMO keeps being very low. Yeah, 0 risk is always better, but hell, everything has risks, we must find the point in which the risk is so low that is worth it, which is the case here IMO.

 

[mrgoogfan]

/unsubscribe

 

[Benm]

The blink reflex is not as fast as 1/100th of a second, in fact, it takes about 1/4th of a second between stimulus and closing of the eyelid.

The whole blink reflex story is about the border between classes 2 and 3. It is supossed that for visible power levels up to 1 mW directly into the eye, the blink reflex is fast enough to prevent damage under normal circumstances. When considering an audience, you must assume the circumstances are not normal however: subjects may be on alcohol, drugs, or even try to stare into a laser beam and stand the pain for sports. So class 1 is actually a fair limit in such scenario.

Class 3A/3R is a different story. It accepts that it IS possible to get eye damage from lasers between 1 and 5 mW in power, but that this scenario is UNLIKELY to occur when handing the laser carefully. This means that shining a laser of 1 to 5 mW in power directly into your eye is NOT a safe practice.

Class 1 is for laser illumination that can do no eye damage regardless of conditions in healty persons. This is comparable to any other light source of equal intensity, and would apply to looking into a lamp at close range (though the IR component makes lightbulbs -more- dangerous in practice). The limit for this is about 0.3 mW directly into the eye, depending on precise wavelength.

 

[mfo]

Wow, why are we still debating this? Keep the lasers out of your eyes at all costs. What's so hard to comprehend about that?