Date:         Tue, 11 Aug 1998 14:34:53 +0200
Reply-To:     "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Organization: RRZE (Regionales Rechenzentrum Erlangen)
Subject:      Re: Driving/Fog Lights
Comments: To: David Bogle / Architecture <bogle@BWAY.NET>
Comments: cc: Vanagon@VANAGON.COM
In-Reply-To:  Msg <35CED261.6384AE07@bway.net> of 1998- 8-10 06:58:41 -0400
              from bogle@BWAY.NET
Content-Type: text/plain; charset=us-ascii

Hi everybody,

On Mon, 1998-08-10 06:58:41 -0400, David Bogle / Architecture wrote:

> ...
>                                                  I learned that the light from
> burning sodium, a "yellow" light, was not only in the middle of the visible
> spectrum, but that its frequency or wavelength was the same dimension as the
> diameter of a typical water droplet in fog!  ...
> ...
>                                                         Of course, some of it
> is reflected back, but overall the depth into the fog which one can see with
> yellow light is greater.

This is all perfectly right.  If by some physical  process you manage to
produce yellow light in  the first place, you'd  probably be better  off
using  this for fog  lights.  But current fog   lights use tungsten type
bulbs, and thus produce a more or less evenly distributed mix of all the
wavelengths ("white" light).  And then everything but the yellow part is
more or less  filtered out and  as an unwanted but inevitable by-product
the yellow part itself is reduced  in strength, too.   That's why I said
use white glass  and let the fog  do the filtering.   Most  of the light
comming back to you will then be in the yellow range, anyway.

Sincerely
 Rainer

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| Rainer M Woitok                  | Phone: (+49-9131) 85-7811, -7031  |
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