Choosing Astronomical-friendly Lighting Sources

From the light-polluted sky spectra, astronomers discovered NaD (a chemical form of sodium) and Hg (element mercury) emission lines. They originated from artificial high pressure sodium lamps and mercury-contained fluorescent lamp. These emission lines located within the range of visible light and affect ground-base optical astronomical observations. Low pressure sodium lamps are better for astronomical observations. It is because the emission lines of low pressure sodium lamps occupy a small portion in visible spectrum only. Astronomers can easily filter out its lines by applying filters, etc.

Sodium lamps

(From 'La Palma night-sky brightness', Isaac Newton Group. Credits: Chris R. Benn)

Spectrum of a moonless La-Palma sky taken with the William Herschel telescope on March 1991. Several features of airglow can be seen in this spectrum of the night sky, such as the emission from neutral Oxygen atom (labeled by OI), and Oxygen molecule (O2). Several lines are caused by light pollution, most notably the emission lines from sodium-D (NaD) and mercury (Hg). The range of the U, B, V, R, and I filter passbands are also shown.