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How Much Laser Power Gets Through Goggles

brendon7358

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I have noticed that unless the laser is in motion, they will tend to start burning the goggles and that burnt plastic significantly reduces the amount of photons going through. At least until it burns through.
 

Benm

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If you are still standing still while the laser burns through your goggles, you would be a very unobservant person, indeed.
Well, that depends on how quickly in burns through really. If you were using those foil type eclipse glasses it may burn through in well under a second and you might not realize what's going on when focused on some other task.

Then again if you get the proper thick plastic goggles it'll take far longer to cut through those. I've actually tried to do this to so anti-green/blue goggles that were fairly cheap ($20 or something) and it took well over a minute to chew a hole through those at about 1 watt of 445 focused in a fairly narrow spot.

Given the smoking coming off and unpleasant smell from this i'd say you'd probably notice before in punches through. Also i tested this with the goggles on the table, not on my face. Even given a fairly high OD you'd probably still see the laser when it's actually hitting you in the pupil. If you have something that's only ND3 and your laser has an output power of 1 watt, it would still be as bright as shining a 1 mW laser straight into your eye - something you'd probably notice quickly.
 

paul1598419

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That was pretty much my point, if you are wearing actual laser safety goggles. I would never use the thin mylar solar eclipse glasses to try to protect my eyes from a class 4 laser strike.
 

Benm

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Those are burned through so quickly they offer no protection at all except from being grazed by a laser show that does audience scanning badly indeed.

Another thing people sometime use are welding glasses. In theory those should work well, but if you get the automatic ones that only dim when exposed to the bright light of welding they could be too slow to react, or the laser may hit you in an eye but miss the light sensor that dims them entirely.

I'd stick with purpose built laser goggles at all times - they aren't that expensive, and if you get really cheap one you could even sacrifice a pair of them to see how much light they actually block by just sticking them between a laser and a meter. Anything good will drop the power to the meter by a factor of over 100 (usually >>1000), though you can burn through given enough time.
 

hakzaw1

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TO avoid confusion, personally, I never call eye ware for green lasers .... 'red goggles'.. they need to be called what they are and never both.
follow me?

I got a cheap set of green laser glasses in the mail today.. I suggested than Alan(KingKube) find good ones (but NOT the cheapest) and offer them at his ebay store. I said get the ones with the 'numbers' on the frames--Like 200- 440 nm OD 7-- High OD is needed for higher powers.
He ignored my advice .. I see when I look at the pair I won at auction for $1.25!!! with cleaning cloth and one of the nicest zipper cases yet.
the lens is RED but these are NOT red laser goggles.. they work OK for blue and violet but block green about 85-90%.. look well made.(the ear piece slides in and out). and I see NO reason to put them down for being cheap.. these do a super job at protecting from green at lower powers... w/o anything printed on the frames... doing a review w/ testing pics then sending to a new member who asked me about eye protection....and I could not recommend he buy from Alan until I saw myself that they work... Other than eye injuries lasers are very rarely the cause of skin injuries for example.
AND actual 'blinding' is also very rare.

.. Ranger 'Kelli' at Burning Man lost vision in one eye ( and some damage to the other) from a green laser 'prankster' she was intentionally staring at the A55HAT. HE had been doing this for some time ( lasing and dashing)and catching him amid 85,000 people was very hard.. She saw him and he saw Kelli-- she kept her eyes on him and he lased her intentionally.
AND being at night ( or while wearing just sunlasses) our 7mm pupils will be much larger and allowing more laser light to enter the eye.
not good!


(BM last I read was not gong to pay her medical expenses-(or not much)- a go-fund-me has been set up to help her.. I sent some $$ can you do that too please.??.


THAT was the Worst case possible -- horizontal beamage ... at 'eye level' .. subject keeping the laser hitting her face.. repeated lasing of the eyes has a accumulative effect ... AND--- with those conditions the lens of our own eyes can magnify the power of a laser >100 X .. some say AS MUCH AS 1000 X .. =and being horizontal greatly increases chnces for getting a burn to one of the two most sensitive spots in our eyes like the fovea.. everywhere else would be a 'retina' injury.. often not very painful and while leaving a scar on the retina ... no lasting effects.... the 'after-images go away fairly quick & not much impairment of your eyesight.... but a scary A55 close call.

so keep yer beams out of the horizontal plane below 10 feet.

for more on all this I have a LSO thread here at LPF in the 'Tutorial' section . took lots of time to write it..
 
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hakzaw1

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this is important.. and merits a double post...



In my pic are Green goggles from Sanwu. They have the look of a cheap chinese standard for laser goggles. They do a good job of blocking red, but as you can see, I'd guess up to around 5mW still gets through. Not bad, but what if a 1W red hits it?
PLEASE call all eyewear by proper name THESE^^^ are NOT 'Green goggles' green goggles have RED lens BUT it is a mistake to call the by any other name BUT Green (laser) goggles...they are NOT RED Laser goggles!

The worst would be having a confused owner expect them to block the WRONG wavelength.

If this, to you , is not a big deal.... that sure shows poor safety sense!! BOOOOO
 

Nutball

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I'll be more careful in the future, but I was trying to point out that the lenses were green by just calling them green goggles when asked if they were full spectrum goggles, which they are not. I just said "green goggles" not "green laser goggles", but I see how it could be confusing.
 

hakzaw1

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THANKS
many times I have seen eekbay sellers getting this wrong... the listing photos did not match the eyewear title--- most thank me and correct ..some get pissy ...they seem to think this does not matter.
..wrong....
eyesight it too valuable to be taken so lightly..
 

lasersbee

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Perhaps saying "green colored Laser goggles" would refer
to the actyal color of the lenses and "532nm Laser Googles"
would refer to the Laser wavelength the Goggles protect
you from.

Jerry
 

LSRFAQ

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Please see attached from Univ. of Missouri and Laser-Professionals.com Nice chart.
Should be a sticky here.. Very few know what OD means in non-scientist terms.
I'd getting tired of explaining it year after year. Please credit and sticky the attached pDf.
 

Attachments

Benm

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As for the naming of the colours of the goggles:

I guess you could call 532-nm blocking ones 'orange' since their lenses usually have that color, and 660-635 ones 'blue' for the same reason.

But i suppose it should be fairly clear to anyone in their right mind that you need to use goggles that are a different color than the laser you are working with. Seriously, what good could any goggles do you wen you can see the laser beam/dot just as brightly with or without them?!

I guess colloquially you could ask 'please pass me the red laser goggles' from a colleague. They probably know what wavelength you are working on and give you the anti-red ones if you're mucking about a 635, and the anti-green/blue ones if working on 532 or 445 etc.

Also high OD numbers are not required: it's a logarithmic scale. ND3 reduces exposure by a factor 1000, ND4 by 10.000 and so on.

Something like ND7 is mad: if that reduced your eye exposure to 1 mW, it would mean that you are illuminated by 10.000 watts per pupil area on areas not covered by the goggles. Even if i'm royal and give a pupil diameter of 1 cm2, that's a megawatt per square meter, 1000 times brighter than the sun at noon in sahara desert. At this point there is no need to worry about your eyes in particular since you'll be burnt to dust before realizing what went wrong :D
 

paul1598419

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You make some excellent points, Benm. But, you switched from optical density to neutral density in the sentence before your last paragraph. I know what you meant to say, but others might get confused.
 

Benm

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I doubt it would matter much if we mean ND or OD here - the former referring to a 'gray' filter that blocks all wavelenghts and the latter referring to the wavelength of the laser used.

I know what you mean by how this could be confusing, but the effect is so large it just really doesn't matter: if you receive ~100 kW/m2 of monochromatic light (comparable to OD7 at 555 nm) or ~1 MW/m2 (ND7 with white light) your concern is not eye damage, but being set on fire.

The only thing is that sometimes ND filters are denoted with a linear reduction rather than a logarithmic one. You can filters labeled like 'ND8' for photography, that pass 1/8th of the amount of light, instead of 1/10^8 for logarithmic notations. With values over about 2 you can easily tell the difference though: A misnamed ND4 filter would be fairly easy to look through as it passes a quarter of the light, while a properly labeled ND4 filter would pass only 1/10.000th of the light and look pitch black.
 




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