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From: neal@weitek.UUCP (Neal Bedard)
Newsgroups: net.med
Subject: Re: Reading in bad light
Message-ID: <247@weitek.UUCP>
Date: Tue, 6-Aug-85 02:27:15 EDT
Article-I.D.: weitek.247
Posted: Tue Aug  6 02:27:15 1985
Date-Received: Sat, 10-Aug-85 04:49:17 EDT
References: <1528@trwrba.UUCP> <1360@cbosgd.UUCP>
Organization: The Church of Appliantology, Sunnyvale
Lines: 34
Summary: Depth of field, contrast

In article <1360@cbosgd.UUCP>, rbg@cbosgd.UUCP (Richard Goldschmidt) writes:
> In article <1528@trwrba.UUCP>, suhre@trwrba.UUCP (Maurice E. Suhre) writes:
> > This business about vision being damaged by reading in poor light
> > has always seemed like an old wive's tale to me.  If you try to 
> > Maurice
> 
> My understanding agrees with your intuition, that light level is not
> a problem.  Much more eye strain is likely to be caused by the distance
> at which you hold your reading matter.  The closer the worse, because of
> the strain on the muscles in the lens of your eye to maintain focus.
> 
> Rich Goldschmidt     {ucbvax,ihnp4,decvax,allegra,seismo} !cbosgd!rbg

With adequate light the pupil is smaller, resulting in a greater depth of
field. The net effect is that the eye has to accomodate less - very
important in warding off eye strain during extended periods of close work.
By the same token, one should not do near work at too close a distance: back
away from the work as far as comfortable, and/or use reading glasses. Both
tactics reduce the amount of accomodating the eye is required to do.

An excessive light level causes annoying glare and afterimages - think of what
happens when a television camera is exposed to a spotlight: the image pickup
medium is saturated, and its contrast is reduced. Same problem with human
vision, the consequence of which is that one is forced to expend more visual
effort (rereading what isn't clear, squinting, etc.) resulting in eyestrain.

Low light levels also reduce visual contrast, with similar eyestrain results.

Then there are video terminals......

-Neal B.
-- 
"mynd you, m00se bytes kann be pretti nasti"
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