Ο "Brian Tung" έγραψε στο μήνυμα
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[snip]
Urban light sources are almost certainly redder to begin with. The Sun
has an effective temperature around 5800 K, whereas I'd guess that most
man-made lights are around 2000 to 3000 K, something in that neighborhood.
Depends on the lightbulb :*)
The distribution of lighting patterns follows developmental plans closely.
Urban (far from cities, if I recall the term right) areas, tend to be
populated with Mercury lights, contrary to rural areas, which tend to be
populated by Sodium lights.
Reason being that the need for efficiency in urban areas is not so
stringent. From what I recall during my days in the States, many large urban
driveways around Chicago and many Chicago suburbs in 1990 still used clear
High Pressure Mecury lights.
In Europe Mercury lights are slowly becoming obsolete. One can roughly judge
the distance of a particular location to the center of a city, by counting
Mercury lights. Mercury lights have much longer lifespans, so any leftovers
are not replaced readily here. However, even poorer areas, would be
populated by incadescent and CFL's.
So the pattern here is (in Europe), poorly populated areas, incadescent and
CFL, so around 2,300-2,700 K.
Medium sized urban areas: High Pressure Mercury (fluorescent) lights (with
some High Pressure Sodium), so around 4,500 K.
Rural areas: High Pressure Sodium lights and Metal Halide lights, so around
2,200 K, with a tendency to up this to 2,700 (halides).
The pattern may be slightly different in the States, since I had not
observed any CFL or incadescent lighting in poorly populated areas. (Note
that CLEAR High Pressure Mercury lights, go as high as 7,000 K, which indeed
turn the sky bluish).
The sky in Athens glows bright orange, which comes from the predominant
resonances of Sodium, around D1/D2. Unfortunately High Pressure Sodium
lights are not monochromatic, so there is a quite wide band of wavelengths
around D1/D2 which get emitted and polute the sky.
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
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--
Ioannis Galidakis
http://users.forthnet.gr/ath/jgal/
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Eventually, _everything_ is understandable