Sodium vapor lamp

Sodium vapor lamp (in a railway station)

A sodium vapor lamp is a type of gas discharge lamp. Streetlights are a major use. There are two types; the high pressure lamp and the low pressure lamp. The older low pressure one gives only clean yellow light. It is used where the ability to show different colors is not very important. The newer high pressure sodium vapor light emits a broader spectrum, often appearing orange but letting people see a limited range of colors, but is less effective at making light.

These lights contain sodium metal in them. They operate by a spark through a tube that contains the sodium. The sodium emits a yellow color, which produces the light. Because the lamp contains highly flammable sodium as well as toxic mercury in the high pressure lamp, it should not be placed in the trash and must be disposed of properly at the end of its life.

Sodium Vapor Lamp Media

Sodium street lights in Tuntorp, Sweden
An HPS lamp after turning off. The alumina material glows red because it is still hot.
Low-pressure sodium lamp (SOX).
Spectrum of a low-pressure sodium lamp. The intense yellow band is the atomic sodium D-line emission, comprising about 90% of the visible light emission for this lamp type.
Two Honda Fits under low-pressure sodium lamps. Both appear black, even though the car on the left is bright red, while the car on the right is actually black.
High-pressure sodium lamps (SON).
Spectrum of high-pressure sodium lamp. The yellow-red band on the left is the atomic sodium D-line emission; the turquoise line is a sodium line that is otherwise quite weak in a low pressure discharge, but becomes intense in a high-pressure discharge. Most of the other green, blue, and violet lines arise from mostly sodium but also mercury lines.
Diagram showing the spectral output of a typical high-pressure sodium (HPS) lamp
Office building illuminated by high-pressure sodium lamps
Warm-up phases of a 70W HPS/SON lamp on a DW Windsor Strand B fitting. The faint white glow of xenon from the arc struck in the arc tube is quickly and gradually replaced by the orange glow of the metallic sodium vapour.