From: Matthew J Ghio <mg5n+@andrew.cmu.edu>
Date: Tue, 15 Mar 94 20:53:03 PST
To: cypherpunks@toad.com
Subject: Re: IR Blocking.
In-Reply-To: <9403160244.AA02855@axiom.maths.uq.oz.au>
Message-ID: <ohVd0sC00VoyM6gF1I@andrew.cmu.edu>
MIME-Version: 1.0
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Peter Murphy <pkm@maths.uq.oz.au> wrote:

> One idea that I thought about is to simply use frosted glass. The police/
> /FBI/CIA/other using the IR cameras don't just want to recieve IR light;

The FBI and CIA are operating in Australia now?  wow...  :)

> they want it in a coherent pattern. Using frosted glass, the light is
> dispersed in (mostly) all directions. The spooks should then only be able
> to percieve some fuzzy shapes. Oh, they'll be able to know if the lights
> are on, but for all they know, you are just having a quiet game of bridge.
> (I am not absolutely certain about the va .. veracity of this method, but
> I gathered that if frosted glass disperses normal light, it should do the
> same for IR. The range of refractive indices would be different, and that's
> about it.) Any criticisms of this method would be appreciated. Peter Murphy.

Acutally, since longer wavelegnths are scattered at greater angles,
frosted glass will scatter infrared better than visible light.  It
probably doesn't amount to a large difference tho...and if it did, they
might move up to ultraviolet.  But UV is much easier you to detect, so
they probably wouldn't risk it.  :)