Xref: utzoo sci.med:4442 sci.electronics:2444
Path: utzoo!utgpu!water!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: sci.med,sci.electronics
Subject: Re: is low power laser light dangerous?
Message-ID: <15571@onfcanim.UUCP>
Date: 6 Mar 88 22:04:51 GMT
References: <602@anasaz.UUCP> <982@ssc-bee.ssc-vax.UUCP> <670@morningdew.BBN.COM> <4428@watdcsu.waterloo.edu>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Organization: National Film Board / Office national du film, Montreal
Lines: 37

What does "Science" call a "low power laser"?

The Class II visible lasers are "reasonably" safe - these are the ones
with power output below 1 milliwatt, and stickers that say "Caution,
Laser Light, Do Not Stare into Beam".

If I remember correctly, they are relatively safe because of this:
The full power of the beam is not enough to damage your retina if the
exposure time is less than 0.1 seconds, and it takes about that long
to blink.  Thus, if you accidentally get the beam into an eye, you can
blink before there is likely to be any lasting damage.  However, deliberately
staring into the beam can cause damage, just like staring at the sun
or an arc lamp - but it will be uncomfortable, and you should know you're
doing something your eye doesn't like.

Visible lasers above 1 milliwatt are more dangerous, since you may not
be able to blink before damage occurs, and they are thus labelled
"Danger, Laser Light, Avoid Direct Exposure to Beam".  Be careful.

There are also low-power lasers that produce non-visible radiation
(I hesitate to call it "light").  The most common example is the laser
diode source in a CD player - typically 0.4 mW at 830 nm wavelength.
It's no more powerful than a Class II visible laser, but you don't see
it so you won't blink, and thus it is more dangerous than visible light
of the same power.  On the plus side, semiconductor diode lasers
generate beams that diverge rapidly, and when used in CD players the
beam is focused using short-focal-length optics so it also diverges
rapidly once past the plane of the disc, so it's hard to get much
of the power into your eye.  The exception to this is that the beam
is parallel between the laser diode's collimating lens and the
moving lens on the optical pickup - so be careful if you dismantle
a CD optical pickup and then apply laser power.  I've done it, but only 
while wearing safety glasses with a very high density at the laser's
wavelength.

In general, I'd be pretty cautious - there are too many things where
I need or at least enjoy good eyesight to take much risk of damaging it.