My Eyes! My Eyes!

That, again is a huge risk you take by relying on the reflection to "diffuse". Never take it for granted. Always assume the whole dot will reflect off in the same vector.

Even if the reflection is "diffused", it can still be damaging to the eye if it does not appear to be bright at first. It may first appear to be the normal dot reflection, but it can still be as unpredictable as any other reflection.

Take care of your eyes, don't hesitate to wear goggles when in doubt.

Hallucynogenyc said:

15mW used on a spirograph is more than safe IMO. Normal scanners used in shows are far above there...

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Those scanners will never scan the crowd however. Crowd scanning is illegal if the power of each line is too high.

and are we talking about using this against any crowd?

mfo said:

Wrong.

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Meatball said:

Please don't give out this kind of advice. A laser is class 3b because it's power is high enough to do damage to the eye, faster than the eye can blink. So ANY reflection, no matter how fast needs to treated as a great hazard to the eye. When in doubt, wear proper safety goggles. Permanent damage is not always defined the same way.

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15mw on a scanner? Assuming he is scanning it at a decent speed, he said a specular reflection off a ceiling fan blade etc, it would be at least 15 feet. Scanned across the eye once, the total power received at the retina would be on the order of microwatts, averaged out across a line on the retina. Each cell would only receive maybe .5uW, assuming his eyes are focused at infinity (which inside they are probably not)

so, unfocused ~.05mm spot, scanned across the cells at a couple hundred cell lengths a millisecond, is safe imo.

Hallucynogenyc said:

and are we talking about using this against any crowd?

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You mentioned "normal" scanners. Those of which that are normally used for shows won't be directly exposed to the crowd unless the projected beams are weak enough. That was all I was saying...

mrgoogfan said:

15mw on a scanner? Assuming he is scanning it at a decent speed, he said a specular reflection off a ceiling fan blade etc, it would be at least 15 feet. Scanned across the eye once, the total power received at the retina would be on the order of microwatts, averaged out across a line on the retina. Each cell would only receive maybe .5uW, assuming his eyes are focused at infinity (which inside they are probably not)

so, unfocused ~.05mm spot, scanned across the cells at a couple hundred cell lengths a millisecond, is safe imo.

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You are certainly entitled to your opinion. But as a simple, and very safe rule, all reflections are to be treated equally. I've caught some pretty nasty specular reflections in the past, did they do any damage? I don't know. But now I regularly use goggles, so now there is low risk of anything happening.

Where his eyes are focused is not a factor that relates to eye damage. He asked about "ceiling fan brass", which is very capable of reflecting a lot more light than a specular reflection from a ceiling fan blade.

There are way too many factors to consider here before we get too technical about it all. Always advise, that the worst could happen 100% of the time. Nothing less. We can't know what his show environment will always be, so we advise against the worst.

As a rule of thumb, lasers that are brighter per mW are safer to work with, so in this case, the green would be safer than the red.

This has to do with faster triggering of the blink reflex by light that appears brighter, but also with your perception of danger: at say 10 mW, red will look pretty innocent, while green seems 'darn bright'.

Within visible light, the damage is done by the actual power in mW more than by the visible brightness. The latter can be responsible for temporary effects like spots, but real retinal burns are caused only by thermal power.

mrgoogfan said:

15mw on a scanner? Assuming he is scanning it at a decent speed, he said a specular reflection off a ceiling fan blade etc, it would be at least 15 feet. Scanned across the eye once, the total power received at the retina would be on the order of microwatts, averaged out across a line on the retina. Each cell would only receive maybe .5uW, assuming his eyes are focused at infinity (which inside they are probably not)

so, unfocused ~.05mm spot, scanned across the cells at a couple hundred cell lengths a millisecond, is safe imo.

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You seem be very lax in eye safety. Just remember, you only get two.

Thx Benm that's sorta what I was looking for!

mfo said:

You seem be very lax in eye safety. Just remember, you only get two.

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oke:

I think he's just being realistic!

Realistic? By talking about the wrong thing?
OP said "Just mount a mirror on a small speaker". This would mean the beam is stationary a large amount of the time. If this hits a piece of brass in the ceiling and reflects into his eye.. YES he will get eye damage.
If he was talking about a scanner and a moving fan, perhaps it would be safe, but this is a completely different scenario.

I can't believe you gave him positive rep Albert, I had higher thoughts about you than that. If you think someone who has basically only given dangerous misinformation and criticised other members for buying more expensive lasers is a "nice member so far!", you have some serious issues.

Seb

dhattman said:

...Just mount a mirror on a small speaker and aim the laser at the ceiling...

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Is this really the definition of a scanner... :thinking: (honest question, I know nada about them). In any event, I would have hoped that a scanner is more than a laser aimed at a mirrror... :-/

dhattman said:

...if oops the beam hit the cieling fan brass and reflected into my eyes for a split second, any permanent damage?

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YES there is always the chance, even with a <10mW of any wavelength!!! [Note that "damage" is not "blindness"]

Benm said:

...This has to do with faster triggering of the blink reflex...

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Ben, I can't believe I'm reading this from you, with all your experience... :tsk:

LIGHT TRAVELS [much] FASTER THAN YOUR REFLEXES, PERIOD.

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"

mfo said:

You seem be very lax in eye safety. Just remember, you only get two.

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Agreed, +1 rep.

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LOOK. I'm not trying to be some kind of "end-of-the-world-at-hand" preacher here; I handle hi-powered lasers, often without even using my certified goggles. However, I do it in a controlled environment and I triple-check where I will be pointing it before I switch it on.

But aiming a laser at a rotating mirror is not my idea of a controlled environment. Again, I am aware that "professional" scanners are safe to the public, but I would hope that a typical scanner consists of more than one rotating mirror (i.e., a diffuser of some sort), or?

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EDIT: Again, from the same Wikipedia article:

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.

EDIT II: This guy's probably no longer into our hobby... :-/

Traveller, a scanner usually consists of two mirrors turning in a closed loop (galvos). Essentially they just create a vertical and horizontal line, but shine the laser off both at the same time, and you can move the beam to any point within the square they create with incredible speed. Combine this with modulation of the laser, and you can create separate shapes wherever you want within the square.
Professional laser shows also have specific settings for measuring eye safety, making sure no stationary beams ever appear close the the crowd, etc.
Because of very fast scanning of the beam combined with large distances, you can do things like crowd scanning with very high powered lasers and no real safety issues, if all rules are followed.

A mirror on a speaker is just.. a mirror on a speaker. It will not have any safety features. The beam will be stationary a large amount of the time and will most likely cause eye damage if it reflects off anything.

Seb

mrgoogfan said:

If it is moving fast, No.

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god, it's not a scanner, I perfectly know, but... hell, it's 15mW, scanners go up to the watts order. Would you personally use safety goggles to operate that? really?

Brighter is safer because you'll see it coming before, not because you'll blink faster when the beam is already inside. I gave him postivie rep because I don't think giving his opinion about WL being overpriced deserves negative rep. I agree on that too lol

Jaseth said:

Traveller, a scanner usually consists of two mirrors turning in a closed loop (galvos)...

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Thanks :beer: for the clarification. So we do agree that the OP's intentions are far from a "formal" scanner... .

Hallucynogenyc said:

Brighter is safer because you'll see it coming before...

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:banghead: