Sodium lamps are used as street lamps and have a distinctive yellow color.  This is because of the strong pair of lines emitted near 590nm.

They are also one of the most efficient light sources available which is why they are so often used as street lights.

Sodium is also used by astronomers to create a reference 'star' or 'guide star' for calibration.  This is done by using a laser that excites sodium

high in the atmosphere and creates a reference point source for correcting atmospheric effects in images. You see some of the same atmospheric

effects on a hot day such as a mirage.  https://www.llnl.gov/str/Guidestr.html

Return to Guess the Spectrum