Green vs. red laser toys

On Wed, 12 Aug 2009 23:50:36 +0100, Jack Campin - bogus address
wrote:

I'm just back from Hungary and Rumania. I saw a shop in Budapest
that specialized in selling illegal-in-the-UK combat knives to
British tourists. One of the items they were selling was green
lasers, so I assume those had to be powerful enough to be a weapon
(and probably the same type the kids near Edinburgh Airport have).

There have been occurrences reported to the UK CAA of pilots seeing
lasers, which could be distracting. You also could cause the same
trouble with a tightly focused spotlight. They don't put mandatory
occurrence reports on line, at least not where I could find them, so
actual details are lacking. This would affect aircraft taking off or
landing, which would be the only times you could possibly shine a
laser into the cockpit window from the ground.

Someone came up with the name laser lout, which makes a good headline.

Pocket lasers, including the green ones, sold to lecturers are 5 mW or
less and are not dangerous. We use green laser pointers to point out
stars to the public at astronomy club events and haven't put out an
eye yet. We use green lasers because the red ones are hard to see.

Bud

On Wed, 12 Aug 2009 19:01:52 -0500, William Hamblen wrote:

On Wed, 12 Aug 2009 23:50:36 +0100, Jack Campin - bogus address
wrote:

I'm just back from Hungary and Rumania. I saw a shop in Budapest that
specialized in selling illegal-in-the-UK combat knives to British
tourists. One of the items they were selling was green lasers, so I
assume those had to be powerful enough to be a weapon (and probably the
same type the kids near Edinburgh Airport have).

There have been occurrences reported to the UK CAA of pilots seeing
lasers, which could be distracting. You also could cause the same
trouble with a tightly focused spotlight. They don't put mandatory
occurrence reports on line, at least not where I could find them, so
actual details are lacking. This would affect aircraft taking off or
landing, which would be the only times you could possibly shine a laser
into the cockpit window from the ground.

Someone came up with the name laser lout, which makes a good headline.

Pocket lasers, including the green ones, sold to lecturers are 5 mW or
less and are not dangerous. We use green laser pointers to point out
stars to the public at astronomy club events and haven't put out an eye
yet. We use green lasers because the red ones are hard to see.

Bud

A handheld laser pointer is unlikely to cause permanent blindness at the
distance from the ground to a landing or taking-off aircraft, but even
dazzling the pilot's vision for thirty seconds or so could cause a crash
under those circumstances. At indoor range, a handheld laser can indeed
cause permanent vision damage if the beam happens to focus onto the point
where the nerve bundle attaches to the retina. The problem is that, even
though the total power of the beam is low, it focuses down onto a very
small dot at the back of the eye, so the power level at that focal point
can be high enough to cause permanent damage.

--
John F. Eldredge --
"Reserve your right to think, for even to think wrongly is better
than not to think at all." -- Hypatia of Alexandria

On 13 Aug 2009 03:07:11 GMT, John F. Eldredge wrote:
A handheld laser pointer is unlikely to cause permanent blindness at the
distance from the ground to a landing or taking-off aircraft, but even
dazzling the pilot's vision for thirty seconds or so could cause a crash
under those circumstances. At indoor range, a handheld laser can indeed
cause permanent vision damage if the beam happens to focus onto the point
where the nerve bundle attaches to the retina. The problem is that, even
though the total power of the beam is low, it focuses down onto a very
small dot at the back of the eye, so the power level at that focal point
can be high enough to cause permanent damage.

You have a cite for a 5mw laser causing permenant eye damage?

Try this test: go to the garage. Turn the car's headlights on.
Shine a laser pointer on the wall where it is illuminated by the car's
headlights. No dot? It is invisible because the car's headlights are
so much more powerful.

Of course, a laser doesn't disperse like a car's headlights. At
200' a laser pointer is going to be brighter than a car's headlights.
But at anything less than about 20', a car's headlights are far
brighter.

Originally Posted by Ted Davis[_3_]

On Wed, 29 Jul 2009 08:52:03 +1000, Yowie wrote:

Just by definition a red laser is far less energetic than a green laser,
and thereby a red laser dot is far safer, eye wise, than a green one of
input power.

However, green lasers aren't the same technology and are far less
effecient. The common red (and less common, blue) lasers are just a power
source and a laser diode - green ones use a near infrared laser diode to
excite some other kind of laser in the far infrared, and that is then run
through a frequency doubler to get green. This one is in the 5mw or
less class, as are most of the red ones. I am very familiar with lasers
(up to the 10 kilowatt level) and make sure *never* to point the beam
anywhere near an eye, anybody's eye, regardless of the power class.


As to the ability to see said dot, whilst perhaps cats don't register
the colour 'red', they would see a very bright spot of light. Suki also
chases the light spot from a regular everyday torch so its probably not
the 'red' that they chase so much as the fact that its an area that is
of high contrast from the background, and it moves around in an
intriguing-to-cats sort of way.

I'd be wary of using a green laser for cat greebling games, but thats
just me - lasers are one of the things I have to work with and I"m
forever filling out risk assessments and having to put danger signs and
extra guarding in - perhaps this makes me hyper aware and therefore a
little paranoid about them. I am not aware of any studies regarding the
dangers of the laser pointer and cats eyes, but there's probably a few
articles in veterinary journals if one cares to do the research.

As I implied, I too, work around lasers, but I'm not afraid of them as
long as strict safety rules are adhered to (something some of our faculty
and students often ignore, as chips in concrete block walls, holes through
wallboard walls, and burned paint spots in various places indicate).

--

T.E.D. )

Wow. I can't believe this thread has existed for three years and not one of the responses above actually answers the original question. I am considering buying a laser pointer for my cat and today (2012) there are lots of options with regard to color and power and class-- I don't want to hurt my kitty (!) but I do want to give him quite a show-- he responds well to red, but would he respond even better to green?? Does no one really know the answer to this question??!

Update: apparently all of the answers to the universe's questions exist on YouTube. I just watched a video of a cat exposed to a dancing green laser dot and then a dancing red one. The cat didnt even seem to notice the green dot. But when the red one came on, it didn't take the kitty long to take notice. Here is the video, see for yourself: youtube.com/watch?v=Bj0C7mLG4DQ.

Which means, the answer to the question appears to be that RED is the preferred color, all other things being equal.