Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!pyramid!prls!philabs!pwa-b!mstr!network
From: network@mstr.hgc.edu (craig chaiken)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Visual perception (was Re: Photographing PC Screens)
Summary: The actual light source doesn't get dimmer
Message-ID: <717@mstr.hgc.edu>
Date: 29 Mar 89 04:56:42 GMT
References: <3779@peora.ccur.com> <3939@kuhub.cc.ukans.edu> <7454@pyr.gatech.EDU> <698@gvgspd.GVG.TEK.COM>
Distribution: na
Organization: The Hartford Graduate Center, Hartford, CT.
Lines: 18

In article <698@gvgspd.GVG.TEK.COM>, mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti) writes:
> In article <29050@sgi.SGI.COM> donl@glass.SGI.COM (donl mathis) writes:
> >When i get two feet away from my monitor, it sure doesn't *seem* to be
> >four times as dim as when i'm one foot away!  And when i'm several
> >miles from Halfdome, it sure doesn't seem any dimmer than when i'm
> >right at the base.  And a light bulb doesn't seem to get any dimmer
> >when i back away from it.
A light source does not get dimmer as you move away from it.  If this
were the case, then the moon would be very dim.  Rather,
the surface area lit by the source becomes dimmer with increasing
distance.  The reason is that the light source is spread over an
increasingly large surface area.  If you focus an image of the moon
through a lens, however, it will be equally bright (more or less)
from any distance.

Craig Chaiken
Hartford Graduate Center
Computing Services