[sci.electronics] is low power laser light dangerous?

eli@lf-server-2.BBN.COM (Steve Elias) (02/18/88)

	(followups sent to sci.med)

	i'm sure someone will correct me if i'm out of date, but...

	the last i heard (Science magazine a few years back), there
	has been no documented case of permanent vision damage from direct
	exposure to low power lasers.  

	the article described a scientist who looked into a low power
	laser on purpose.  weird spots were visible on his retina when
	it was viewed with a microscope, but he had no permanent vision damage.

bmaraldo@watdcsu.waterloo.edu (Commander Brett Maraldo) (02/19/88)

In article <670@morningdew.BBN.COM> eli@BBN.COM (Steve Elias) writes:
>	i'm sure someone will correct me if i'm out of date, but...
>
>	the last i heard (Science magazine a few years back), there
>	has been no documented case of permanent vision damage from direct
>	exposure to low power lasers.  

    I have worked with, and been exposed to, the light from both 1mW and
    5mW HeNe lasers.  Due to my carelessness I have had the light from
    these devices enter my eye, unobstructed.  

    I did not sustain any damage that caused a long lasting change in my
    eye-sight.  As for pin-holes in my retinas, I can't comment as I
    haven't had my eyes checked since.  I urge anyone working with lasers
    of any sort - use EXTREME caution, treat the beam as a death ray and
    avoid ANY kind of contact with it.

    Just for fun, here are some numbers:  A comparison between the photon
    outputs of a 1mW HeNe and a broadband thermal source.

    For the HeNe:  10^16 photons/s into an angle of 2E-6 sr.
    For thermal :  10^9  photons/s into an angle of 2*pi sr
		   (note: that's only 320 photons/s into the same solid
		   angle as the laser!).

    BE REALLY CAREFUL!!!!!!

					Brett L Maraldo


-- 
               --------     Unit 36 Research     ---------
	                "Alien Technology Today"
  	 	    bmaraldo@watdcsu.waterloo.edu 
  	 {allegra,decvax,ihnp4,utzoo}!watmath!watdcsu!bmaraldo

dave@onfcanim.UUCP (Dave Martindale) (03/07/88)

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.