Main Index Sky-Glow Analysis The New Sky-Glow Spectra Evolution of Sky-Glow The Lighting Laws
Up-Light City Spectrographs
Using the easier overcast method, I went around other cities to secure their "up-light" signatures. For such overcast sky-glow spectra, the scattering is always independent of any wavelength and representative of the local up-light.
Is LED lighting good? Is it bad? How can you tell? Downtown Toronto's OVERCAST up-light spectrum:
The city of Kingston, Ontario, Canada, uses LED systems for most of its city streets. But why are emission lines still apparent and distinct?
Some American cities..
Chicago uses some HUGE wattages - 1000w and 400w HPS are not unusual for downtown. The sky-glow of Chicago had a strong orange glow. However, away from the city proper it looked much whiter.
It was a warm and muggy night in Chicago (but otherwise clear) when the following 2 spectra where obtained from the same spot. (Schiller Woods, near W. Irving Park and N. Cumberland Ave). Aiming east, then west, about 30 minutes apart, the two spectra were differenet. The same equipment and settings were used for both, except for the exposure times in seconds shown on the image.
How bright is Las Vegas? It's bright, and I know exactly what that brightness is made up of; the spectrum appears just a little different from other cities.
How about a CLEAR night spectrum? The Los Angeles sky-glow (acquired from an isolated spot on Griffith Park):
L.A.'s sky-glow spectrum was not a big surprise; the city had converted its street-lights to LED back in 2014. On nice and clear nights a blue sky-glow is created.
In order to subtract man-made emissions from their data, professional astronomers analyze and catalogue sky-glow. And although that information can be found by anyone, data are from darker observatories commonly removed from the typical urban sky-glow of many amateurs - as seen above.
Therefore, there's a disturbing gap in the knowledge of actual and tangible urban sky-glow spectra in any astronomical literature - online or elsewhere. For the big cities, dated estimates of sky-glow are often found and the only assumed sky-glow emissions are the sodium and old mercury spectral lines. Just by glancing at the spectra above, astronomers need worry about a great deal more.
Nineteen years into the millenium, it's time to update the info on the spectra found in urban sky-glow.
Here's the New Sky-Glow!