FROM: Marcangelo Puccio 
SUBJECT: Re: Night Vision Green?
DATE: Mon, 05 Apr 1999 21:40:11 -0700
NEWSGROUPS: sci.optics,sci.physics

Jim Mansfield wrote:

> In article <37091C73.7E228490@alcyone.com>,
> Erik Max Francis   wrote:
> >Thomas Jaworowski wrote:
>
> [snip night vison goggles being green - I haven't a clue why they are]
>
> >I haven't heard of that, but the Sun's frequencies peak at green, so it
> >makes sense that we would see best at around that peak frequency.  Also,
> >it's awfully convenient of chlorophyll (and other such molecules) absorb
> >energy around the peak frequency, in order to maximize the amount of
> >available energy available for photosynthesis.
>
> Doesn't there seem to be something conflicting about plant leaves _looking_
> green (ie, reflecting green light) and their absorbing energy at the
> Sun's peak frequency of green? Chlorophyll has absorption maxima in
> the blue and, to a lesser extent, in the red.
>
> -Jim
>
> --
> Jim Mansfield                          Internet: Jim.Mansfield@nrc.ca
> National Research Council of Canada    Phone:    (204) 984-5191
> Institute for Biodiagnostics           Fax:      (204) 984-5472
> http://www.ibd.nrc.ca/~mansfield/

Yes - you are right.

Plants photosynthesize poorly at best if illuminated by light at around 530
nm.  The following numbers are rough, but peak absorption in the red end is at
around 650 nm for Chlorophyll-a and at around 670-680 for Chlorophyll-b.
Peaks in the blue end are at around 440 and 460, respectively, with absorption
minima between 500 and 600 nm.  Some plants have 'accessory pigments' that are
able to absorb light pretty well in the 500 nm range (i.e., carotenoid piments
like beta carotene).  These form part of an 'antenna complex' that channels
energy from these other wavelengths to the chlrorophyll molecules that are the
core of the photosystems.  Some aquatic 'plants' (algae, actually) have
radically different absorptions that reflect the fact that certain wavelengths
of light are absorbed or reflected from sea water (i.e., red and golden algae
or 'seaweeds').

Not that this is a photobiology newsgroup... just had to comment!

-Marco





From:             "Mark Burton" 
To:               
Subject:          Question about Night Vision Goggles
Date sent:        Sat, 25 Aug 2001 22:42:08 -0400

This is a response to an article on your website that I would like to add
to. The "Details about IR-reflection of foliage" has a question about why
night vision goggles are green. They aren't actually, they are filtered
green because the human eye can naturally distiguish the most shades in the
green area of the colour spectrum.

If that question hasn't been answered somewhere else for you already, I hope
this sheds some light on the subject.

Regards,
Mark Burton

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