Green lasers: how much power is too much?

[dotancohen]

I saw some green lasers on dealextreme recently, they have units that go up to 200 mW:

DealExtreme: $59.99 200mW Green Laser Pointer Pen Black

This thing looks a bit unsafe to me! My intention is to show the daughters some stars here in our polluted skies, not much else. How much power is needed for that? How much is dangerous? I will be the only one handling the device, so I am not concerned with someone pointing the laser at their friends' eyes (I treat the tool like a firearm).

Thanks for any advice.

[Bigwings]

Then you only need a green 5mW laser pen as sold on a number of astro sites.

Anything above that and you could be storing up problems...just think kids getting it and looking at the beam.... I know you would be careful but ....accidents do happen.

If you get a high power laser then buy a battery factory as well. They do eat batteries

[dotancohen]

If I can keep the firearms safe them I can keep the laser safe. Are the 5 mW lasers adequate? Would I be much happier with a 20 mW or even 50 mW model? Are they really that dangerous when used for their intended purpose?

[brianb]

Are the 5 mW lasers adequate?

More than enough to blind drivers & pilots.

You don't even need 5 microwatts. Buy a proper finder instead.

[blinky]

I have a 5mW and it's fine, I have seen a 20mW and it was very bright but honestly 5mW is fine - I have used it for exactly what you are going to use it for.

[dotancohen]

> More than enough to blind drivers & pilots.

> You don't even need 5 microwatts. Buy

> a proper finder instead.

Thanks. As you say that the 5 mW is adequate I will simply go with that. I would not deliberately point the device at aircraft, but I do get your point.

[Herakles]

I use the 5mW , more than does the job , touches the stars it seems. Anything stronger ( IIRC ) is illegal I'm sure.

[dotancohen]

Does anybody know about the IR dangers of the laser? I see that some of the lasers warn that they have no IR filters. But at a fixed 532nm wavelength, what IR is there?

[Herakles]

Used properly, safely ( like anything ) it should be fine. Google is your friend....

IR dangers of the laser - Google Search=

[Mikea]

I would not want to be in the vicinity of a handheld laser of more than 5mW, let alone 200mW. 200mW would be a Class 3B source and not eyesafe. The sale of these things should be banned.

Anything Class 2 (1mW max) or lower should be relatively safe.

5mW (now called Class 3R) should be ok in sensible hands.

[calibos]

5mw will not blind pilots or drivers. It will however distract them and we all know what can happen when drivers or pilots are distracted. The 5mw is not dangerous to their eyesight but a close encounter with a wall or lampost or the ground can be detrimental to their health. So the basic point about not pointing any laser at drivers or pilots still holds but the way the point was made is like saying a kitchen knife can kill, ban them and use a spoon instead. Remember guys, recommending another type of finder is for those thinking about scope mounted GLP's. There is no 'good' alternative to pointing at stars to groups which is what the OP is talking about.

That said, a 200mw GLP is for the balloon popping and plastic bag melting brigade.\

5mw is fine if a bit dim for anyone not standing within about 3 or 4ft of you. If you don't mind ignoring the 5mw+ ban then I would go for a good quality (ie. Gauranteed output and IR filtered) 10mw. Those are 'wickedlasers'

[dotancohen]

Thanks, Herakles, this thread is one of the top results!

I did google before posting, but all I found was very general information. Nothing that would concretely answer this question:

"What are the dangers of operating a 200 wM laser when pointed at the sky at night, at least 60 degrees away from any bystanders and not aimed at humans, aircraft, or other likely-inhabited structures. The person operating the device is a trained combat soldier and would treat the laser as he would any other weapon."

I probably should have asked it exactly that way to begin with!

[dotancohen]

> 200mW would be a Class 3B source

> and not eyesafe.

Not eyesafe if

1) pointed at the eyes?

2) pointed at a typical nearby surface and the resulting dot observed?

3) pointed at the sky at night at least 60 degrees away from humans who will be looking in the opposite direction?

> The sale of these things should

> be banned.

It is in many countries, but not my own. Therefore, if a responsible adult will be operating and handling the device, can it be used in a safe manner?

[Milamber]

Then the answer is yes, if you are prepared to take the implied responsibility that your actions will not have any detrimental effect on those around you. It cannot be anything other than yes in this situation - and personally I hate the damned things!

Remember though that point (2) above should not be even a mildly reflective surface since even 10% reflection is going to hurt - at 200mW your laser will be continuous rather than pulsed, reducing the pupil's chances of constricting in time to prevent damage.

Arthur

[acey]

My intention is to show the daughters some stars here in our polluted skies

You mean add to the pollution? I applaud your aims, not your method. I assume you don't let your kids throw sweet wrappers on the street, so why teach them to shine lights in the sky?

Take a cardboard tube (e.g. from a roll of clingfilm or baking foil), and fix it in place (e.g. on a photo tripod) so that your daughters can see which stars you are trying to indicate. If you want to get really hi-tech then add cross-hairs. This was the sort of method that people used for thousand years, prior to the invention of lasers (or even telescopes).

[themos]

so why teach them to shine lights in the sky?

You mean, why normalize that behaviour. My answer is that I have no reason to believe that my behaviour affects what my children are going to do in their lives. I can enforce some family rules in a narrow context and that's about it.

I shine the odd laser in the sky because I don't mind other people doing it, yet. When I start minding, I'll stop doing it, I expect.

[dotancohen]

> Remember though that point (2) above

> should not be even a mildly reflective surface

> since even 10% reflection is going to hurt - at

> 200mW your laser will be continuous rather than

> pulsed, reducing the pupil's chances of

> constricting in time to prevent damage.

I see. I am leaning towards the 10 mW or 20 mW unit, then. I see that dealextreme does not have a version with an IR filter, so I will look around for a model with such a filter.

> You mean add to the pollution? I applaud your

> aims, not your method. I assume you don't let

> your kids throw sweet wrappers on the street, so

> why teach them to shine lights in the sky?

I don't even let them eat sweets!

So far as I understand, energy pollution differs from particle pollution in that it is not cumulative. So while shining the laser at the sky will increase the total light output of my city into the sky, the second that I disable the laser the sky will return to it's previous state. Furthermore, the cause justifies the method: would you not suggest flying our world leaders to the Kyoto Protocol meetings because the airplanes burn fuel?

[brianb]

So while shining the laser at the sky will increase the total light output of my city into the sky, the second that I disable the laser the sky will return to it's previous state.

... and screw everyone that happens to be receiving excess photons in the meantime?

Furthermore, the cause justifies the method: would you not suggest flying our world leaders to the Kyoto Protocol meetings because the airplanes burn fuel?

I would suggest very strongly that, given the quality of modern comminucations, it is no longer necessary for politicians, heads of state, businessmen etc. to fly around the world - they can do all the necessary work over the network. And I don't see why taxpayers (or customers) should have to pay the expense of the associated junketing.

If they must travel round the world, give them a rowing boat & a pair of oars.

[themos]

Has there been any documented case of a laser ruining anyone's endeavours (star parties apart)?

[brianb]

Has there been any documented case of a laser ruining anyone's endeavours

There are loads of reports from pilots & drivers. That's really dangerous. Now here's the point - a laser pointer does nothing that an ordinary finder doesn't do better - so why have the thing in the public domain where it can be misused?

I'm against restrictions in general, but I really do feel that lasers need to be much more tightly regulated i.e. operating licences required for any device with an output exceeding 10 microwatts and/or used outside a secure enclosure.

[kniclander]

Now here's the point - a laser pointer does nothing that an ordinary finder doesn't do better .

surely not true? if you've got 5 kids next to you, and you want to say, "that star there", isn't a laser pointer better?

[themos]

There are loads of reports from pilots & drivers.

Undoubtedly. But has any stargazer/astronomer ever had a session ruined?

[Milamber]

Several, which is why they are pretty much banned from organised star parties. Yes, I know you said star parties apart in an earlier post, but that's like saying "Has anyone here shot anyone... soldiers and maniacal killers apart" is it not?

Arthur

[themos]

It's a genuine question, Arthur. You are setting up on your own, or with others, and someone not in your party ruins it by playing with a laser. Has it happened?

I've had club lights, fireworks, security lights, street lights, plane/copter lights but I cannot recall a single instance of a laser affecting anything. Others have clocked far more hours under the stars so I am asking.

[dotancohen]

> and screw everyone that happens to be

> receiving excess photons in the meantime?

Could you please elaborate on how they are screwed by my extra photons, or how that even affects anybody? Serious question, I may need to learn something

> I would suggest very strongly that, given the quality of modern

> comminucations, it is no longer necessary for politicians, heads

> of state, businessmen etc. to fly around the world - they can do

> all the necessary work over the network. And I don't see why taxpayers

> (or customers) should have to pay the expense of the associated junketing.

either you are joking or you have no experience in business relations. I cannot imagine governments being much different. Or do you think that the only time Leader A meets Leader B should be when he is looking down the barrel of a rifle?

> a laser pointer does nothing that an ordinary finder doesn't do better - so why

> have the thing in the public domain where it can be misused?

Stay steady _in_my_hand_ while four other people see what I am pointing at?

>I'm against restrictions in general, but I really do feel that lasers need to

> be much more tightly regulated i.e. operating licences required for any device

> with an output exceeding 10 microwatts and/or used outside a secure enclosure.

I agree with this completely. Make sure that the devices are only in the hands of the responsible. My questions were assuming that I am responsible with the device, and that nobody else would operate it.