Date: Sun, 09 Feb 2003 20:13:22 -0500
To: WSFA members <WSFAlist at keithlynch.net>
From: Sam Pierce <scpierce at alum.mit.edu>
Subject: [WSFA] Re: invisibility cloak
Reply-To: WSFA members <WSFAlist at keithlynch.net>

Great analysis, Ron, but I left out one significant detail.  The demo was
done on the sidewalk of a major city street, in bright sunlight.  The
surface receiving the projected image is also in direct sunlight.  Just a
minor complication.

                 -- sam

At 02:49 AM 09-02-03 -0500, you wrote:
>I'm not surprised that the demo was unimpressive, but not because the
>displayed background image seemed too dark.  That problem alone could be
>fixed by adjusting the brightness of the display, a seemingly simple fix,
>in principle.  And the brightness problem may have been caused by the
>unusually bright lights used in TV studios to illuminate the subjects (if
>the demo was done in a studio).  The subject was presumably
>well-illuminated by the studio lights, but that unusually large amount of
>extra light may have 'washed out' the display to some degree.  The
>display brightness might have been correctly adjusted for typical
>lighting conditions.  They might have forgotten to correct for the
>unusually strong studio lighting, or more likely, the display could not
>be made bright enough to do so.  An ordinary TV screen is difficult to
>view in typical outdoor daylight, and is nearly impossible to view when
>strong sunlight happens to be shining directly on the screen.
>
>It would be quite difficult to implement a highly effective invisibility
>'cloak' using a display which is flexible and which has an ill-defined
>shape, like a typical cloak or trenchcoat, even if the invisibility is
>only intended to affect observers looking from a single direction.  The
>logical shape for an invisibility shield which needs to work in only one
>direction would be a flat panel, for a shield which is to work in all
>horizontal directions, a cylinder, and for a shield which is to work when
>seen from any direction in three dimensions, a sphere.
>
>Ron Kean