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From: ebstokes@maxwell.crd.ge.com
Newsgroups: sci.optics,sci.physics,sci.chem,bionet.general
Subject: optical density
Message-ID: <18071@crdgw1.crd.ge.com>
Date: 30 Mar 91 20:59:31 GMT
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Organization: General Electric Corp. R&D, Schenectady, NY
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I am interested in finding out if there exist alternative definitions
of "optical density" in different disciplines. That is, does a
physicist mean the same thing as a biologist when she says "optical
density". I'll start by stating what I mean when I say "optical
density". If a beam of light has an initial intensity I0 (in watts,
for example, or watts/(unit area)), and then the beam passes through a
medium of optical density 'od', then the intensity of the beam of
light after passing through the medium is:

	I = I0 * 10^(-od)			(1)

Taking the base ten logarithm of equation (1) then yields an
expression for 'od' in terms of I/I0:

	od = -log(I/I0)				(2)

I am, for the record, a physicist.

Ed Stokes
ebstokes@crd.ge.com