[Tig] color perception of lights

Martin Euredjian ecinema
Tue Oct 16 20:14:33 BST 2001


From: "Rob Lingelbach" <rob at film.calarts.edu>


> I've always noticed that from an airplane, sources of light on
> the ground have a very distinct hue, for example streetlights in
> the U.S. will be quite blue or quite amber (mercury vapor vs.
> sodium).  In Rio de Janeiro ...

> When I'm walking around on the ground and look at these same light
> sources their color is not as distinct.

The clue here is "air" as opposed to perfect vacuum. The atmosphere passes
the aprox. 380nm to 780nm range of human visual perception quite well at
short distances.  It actualy goes way out to the 10um region in a very bumpy
way.  Here's a very interesting graph
http://fuse.pha.jhu.edu/~wpb/spectroscopy/figures/trans.gif

The "stuff" between you on the plane and the ground will act as a filter and
let certain portions of the spectrum reach you with greater intensity than
others, hence the color your mind sees.  I guess there's different "stuff"
in the air over Rio than over Los Angeles.  :-)

This, BTW, is the reason that the Sun appears red during sunrise/sunset
hours.

A much more pronounced effect is had underwater, as every diver knows.
While it takes thousands of feet for the effect to be seen in air, it only
takes a few feet under water.

There's also the fact that aircraft windows are not perfectly clear, that
you are looking through two or three panes of plastic and at a high angle of
incidence.  I don't know if different models of jets have different types of
window material.  This effect could be a lot more significant than whatever
air could do.  What do lights look like over an island in the middle of the
Caribean on a clear day?


-Martin Euredjian
eCinema Systems, Inc.
(661) 305-9320
ecinema at pacbell.net









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