Re: bmw-digest V9 #576

["David W. Peters" <peters@xxxxxxxxxxxxxxxxxxxxxx>]

> Date: Mon, 23 Nov 1998 17:59:37 -0500
> From: David Beatty <dbeatty@domain.elided>
> Subject: blue lights
> 
> See below.  Is the jury still out?
> 
> David D. Beatty
> 
> 
> 
> 	-----Original Message-----
> 	From:	Drew Ragan [SMTP:drewragan@domain.elided]
> 	Sent:	Monday, November 23, 1998 5:39 PM
> 	To:	David Beatty
> 	Cc:	mr2-interest@domain.elided
> 	Subject:	Re: MR2 blue lights
> 
> 	This is incorrect!!  I am in the Coast Guard - we are switching
> from red lights to blue for the sole fact that blue is the last color
> your eyes see before you get full night vision.  look at any color chart
> and see that it starts with white - red is between the white and the
> center of the spectrum - the closest color to blach that is useable with
> lighting is what color?  Blue!  Blue is the best color for night reading
> with the least effect of hurting your night vision.  As for the military
> - - blue is in the process of phasing out the red lights!!
> 	drew
> 	93NA

I guess I am like most other people in that I get upset when people
completely misrepresent your area of expertise.  This is just such 
an example.  I think most of us who had seventh grade science can see
the falacy in the attached, but as a refresher remember that "white" 
shows up nowhere in the spectrum, nor does black--I have no idea what 
this "color chart" is, but it has nothing to do with the optical 
spectrum.  White is merely a mix of colors in the visible range of the
human eye, roughly 400nm to 700nm.  Blue is at one end of the visible
spectrum and red at the other.  Our eyes actually respond rather poorly
at the red end and the blue end of the spectrum; they are much more
sensitive in the center region.  Night vision is slightly skewed from
this, and accordingly BMW makes their instrumentation reddish/orange
rather than that horrid green that some automakers use.  The theory
has been stated in other posts: the pupil will not open as much and 
thus return to a wide open state faster when again peering into the 
darkness.  As for what black is: it is the absence of electromagnetic 
energy in the visible spectrum.  It is rubbish to call black "closer" 
to one color than another.

I have not read anything about the Coast Guard changing light colors,
but it is most definitely not for the reasons given.

This addresses nothing about the issue of Rayleigh scattering which 
happens much more in the blue region of the spectrum.  Look for posts
in old digests where I rant about that topic with respect to fog
lights.

Sorry for the rant,
Dave

- -- 
David W. Peters, EE PhD Candidate   	
Optoelectronic Integrated Systems Lab
Georgia Tech

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