Re: Re Laser pointers in 3D and safety

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Mon, 10 Feb 1997 07:26:32 -0600
>From: P3D Peter Homer <P.J.Homer@xxxxxxxxxxxxxxxxx>
>Subject: Re Laser pointers in 3D and safety

>As for safety at the Eastbourne ISU convention some body in the audience
>had a laser pen which they used to do an impromptu light shows between
>slide shows without any harm. I am suprised that a laser pen is as
>powerfull as class III but as already mentioned this is subdivided into A
>and B and IIIA should not do sufficient damage before the eye closes
>autonomicaly IIIB could. 

One reason some pointers are rated so highly on the safety scale may be that
most of them are at wavelengths at which the human visual system has very
low sensitivity, so it takes a comparatively large amount of power for the
spot to look bright. But the eye's defensive mechanisms are based on apparent
brightness, so a beam hot enough to injure the retina may not look bright
enough to trigger these defenses. This is more obviously a problem with
infrared lasers.

>But this does not appply to a focussed beam so
>there may be a problem with opera glasses ,projectionists binoculars or
>even prescription glasses . 

It's ironic that the people with the sharpest vision are the most
susceptible to injury of this kind.

>One further point
>though our laser safety booklet we use at work suggests that even mat white
>screens may not be safe with some lasers and recommends coloured even
>complimentary coloured or black mat screens.                 P.J.Homer

I have a pair of He-Ne laser goggles - are they any good for 670nm laser
pointers? If not, are goggles for the longer wavelengths available?

(BTW - I take it that the discussion of 3D laser pointers referred to their
use in pointing out features on a 3D projection? I'm not sure that was
explicitly stated.)

John R


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