Lasers - was 'LED bulbs damage the eyes?"

[Another John]

Hugh's question reminded me to ask this question: how dangerous are laser pointer "toys"?

AFAIK you can't buy them in this country, but they're easily available elsewhere, and when we were in Canada recently we bought one for our cat to chase (since my son, whose cat it *originally* was!) said she used to love the pointer that he had.

Having got it back home, and seen (without looking into it!) how terribly bright the light is (even when accidentally reflected off shiny surfaces) ... we've never actually used it to amuse the cat. Or for anything.

Furthermore: the other day driving along the local dual carriageway, someone in the car in front (I think) lit up a road sign (it was daylight btw) with a green laser: got me thinking what would happen if the moron concerned decided to point it, e.g., in my direction.

Would be interested see comments, in particular reassuring ones!

John

[michael adams]

While the article states that pocket lasers which fall with US FDA guidelines - and of course not all do - are incapable of causing permanent damage many of the comments at the end of the article appear to contradict this finding. With at least 4 reporting of floating shapes in front of the eyes etc. as a result of being zapped with such devices. How long such shapes are going to persist being the question. The article does make the point that all such devices are capable of causing temporary flash blindness which would obviously not a good idea if driving a car, operating machinery, walking across the road or maybe doing just about anything apart from sitting in a chair

michael adams

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[dennis]

The low power ones don't do permanent damage even if you are silly enough to stare into one. But they can cause temporary blindness and cause you to crash. If you do see someone pratting about with one in a car then a call to the police is in order.

It is possible to make some laser pointers cut metal so they can be made into dangerous devices.

[Jabba]

Another John wrote

laser-1541598389

14 years for pissing around with one.

[Nightjar]

Cats are usually happy enough to chase the light from an ordinary torch.

Plenty of cases of them being pointed at aircraft that suggests you would, at best, have found it distracting. e.g.:

This sets out H&S guidance for the use of laser devices:

[alan_m]

But don't rely on the label to tell you the power. Cheap high power pointers may be marked with lower powers to 'meet' legislation in western countries.

A few years back I purchased a 50mW (it is marked 50mW) green laser pointer from an on-line seller without problems. It's not something I switch on without safety glasses.

A LED focused and sent down a fibre may do eye damage if you are silly enough to look closely at the end of the fibre - especially if the LED is not in the visible band.

[Chris Bartram]

The local rozzers seem to take it seriously.

[Martin Brown]

It is trivial to buy them in the UK and in any colour. They have a few legitimate uses like pointing at stars in the sky for public lectures.

Main problem is with instantaneous flash blindness. Blink reflex or looking away will generally save you from serious trouble. Stare into the beam and you can do real damage (same applies to the sun).

Much more of an issue in a dark environment than in full sunlight. Seriously powerful lasers can produce scarring on the retina.

Most of the technicians in our optics lab had one or two such as it was easier to align the beams for practicals by eye than by the approved safe method. Dark adapted the eye is vulnerable. This was in the days when it was one big laser and a host of half silvered mirrors.

Same happens with deep solar eclipses - the final crescent is still photosphere brightness but the eye's iris is wide open and you can end up with characteristic crescent shaped scars. There are no pain receptors on the retina so you don't feel the damage until much later when the immune response to the damaged cells kicks in. Nasty!

The unfortunate blind physicist Joseph Plateau attributed his loss of sight to staring fixedly at the sun for 25s as an experiment. He did lots of other dodgy stuff with lamps and persistence of vision too.

He was most famous for formulating the rules of bubbles.

[Sam Plusnet]

How does that work?

Illuminating a star which is tens or hundreds of light years away sounds like a tough job.

And quite slow.

[Dave Liquorice]

Odd, other half bought couple last Christmas for me and The Lad. Key ring/mobile phone jobbies, with white LED or red laser. Class III, less than 5 mW output the label says. They runs off 3 x 192 tiny button batteries

Previously I bought a green Class IIb that runs from 2 x AAA, that is a rather bright, enough scatter from motes of dust to be visible, the ones above don't do that.

Our cat liked either for a week or two then got bored and isn't overly keen on chasing them anymore.

[Sam Plusnet]

Cats don't like games where they don't win, & prey they can't get their claws into.

[Brian Gaff]

Well, I'm sure you are aware that police do take a hard line on anyone shining these at aircraft, and as I listen to aircraft a lot, its very common to hear them report green lasers dazzling them from the ground when still at several thousand feet and of course lower. its not the actual power, but the intensity focussed in the beam of course, which is the issue here. I can well remember some of the stage lasers of the past having dire warnings about making sure people are not in the eye line, so I'd imagine things have happened which are not good. Brian

[Martin Brown]

Backscatter of the green laser beam from dust in the air allows you to literally point at a star and have a visible line reach out from your hand and appear to touch it. The beam divergence makes it fade a bit but to all intents and purposes it literally appears to touch the star.

You have to practice a fair bit to hold it steady enough or learn to circle the thing you want to point at in a controlled way.

Typically they are nominal 10-50mW in the green and heaven knows what output of the leaked IR pump laser. They are easily available.

Not something you want to stare into or point at a specular surface!

[michael adams]

There's no need to illuminate it. If you can imagine the night sky is like the inside of a planetaruium then using imaginary measurements. If say the roof of the planetarium is 60 feet high and star A is ten feet away from star B on the inside of the planetarium roof, then a beam of light pointing at star A will definitely be pointing at star A rather than at star B.

Then if you open up the planetarium room, and again point the beam of light at star A, then the same should apply.

michael adams

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[Scion]

Brian Gaff put finger to keyboard:

When laser disco illumination first appeared, it drew pictures or patterns by using motorised mirror mounts to deflect the beam. There had to be interlocks to stop the laser shining in case one of the motors seized and the light was directed to a fixed point.

Dunno if they use the same arrangement now. Must go to a club and check.

[jrwalliker]

Yes, the green ones use an infra-red laser followed by a frequency doubling crystal which is not very efficient.

I have seen reports that the infra-red blocking filter that is meant to follow the doubler is sometimes missing from the cheap ones, so there could sometimes be many hundreds of mW of infra-red together with the green output.

John