Re: Retail scan point

["David Bromwich" <D.Bromwich@ens.gu.edu.au>]

>
> From:          "Randy Ross" <RNROSS@BCSC02.GOV.BC.CA>
> To:            Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>

> Radiation Protection Section
> BC Ministry of Health rnross@bcsc02.gov.bc.ca
> The point is,a scanned laser beam seems bright..."seems" bright to the
> eye.  That means it is bright to the eye.  It's also a laser (fear enters in he
> re).  Try staring into the retail scanner beam.  Yes that's right hold up the l
> ine and don't tell anyone where you work just let them think what they will and
>  you will see if you can manage to get a beam to cross your pupil a few times
> I've done it and it does seems bright!

I cannnot trace the source, but Professor John Marshall at the Royal 
Opthalmic Reasearch Instritute in London told me some ten years ago 
that a flashing light (read laser beam traversing the pupil) seems 
brighere than a constant source.  If you want to make a light source 
appear brigher, modulate its intensity (10's of Hz, I think).  This 
may play some part in the perception of brigtness in the alignment 
lsers.

Hope this is of use

David Bromwich, CIH 
Lecturer, Occupational Hygiene     tel (+617) 8757487
Faculty of Environmental Sciences  fax (+617) 8757459
Griffith University, Nathan Q 4111 AUSTRALIA