[BC] Virtual source location and inverse square

[j...@pobox.com]

On Sun, 11 Mar 2007 09:01:23 -0700,
Jonathan Edelson <winni...@borealis.com> wrote:

> Subject: RE: [BC] Best LED front lights for use with dynamos
>
> At 08:51 AM 3/11/2007, Jacques Bilinski wrote:
> >
> >The qustion is can the virtual light source be behind infinitly behind
> >the light in question? :)
>
> Yes. Think laser :)

Only if you neglect diffraction, which you can't, and which will bring
the virtual source much much closer than infinitely behind.

A laser packs its light into a tiny angle, but if its beam has a finite
radius, it will spread and attenuate in an inverse square relationship,
even in a vacuum.

> I should also add that the inverse square law is itself an
> approximation that presumes a _point_ source.
>
> Consider an infinite plane that is a light source. The light
> intensity would be _constant_ no matter what the distance from the
> plane. From an infinite _line_ source, light intensity follows an
> inverse (1/distance) law.
>
> The inverse square law is an approximation that holds well when the
> distance from the source is larger than the size of the source.

All true.

> -Jon

--
The Pentium III was an improvement over both the Pentium II and the Pentium 4.
John P. Serafin | Operating a bicycle is more like driving than riding.
jps at pobox com | Operating an automobile is more like riding than driving.

--
To subscribe to this list send a BLANK email to bikecurren...@topica.com
To unsubscribe from this list send a BLANK email to bikecurrent...@topica.com
--^----------------------------------------------------------------
This email was sent to: bikecurrent-g...@googlegroups.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?aVxiBc.aBSdFg.YmlrZWN1
Or send an email to: bikecurrent...@topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------