The Sodium vapor bulb or lamp is the type of gas discharge bulb which utilizes the sodium in the energized form in order to produce light. Sodium vapor lamps are of two types such as HPS lamp and LPS lamps. Since the Sodium vapor lamps are better than the mercury vapor bulbs. Most of the cities which have large astronomical research centers use this type of lamps. The LPS uses the arc tube that includes the solid sodium and a penning mixture of argon and neon gas which produces the light. The light discharge tube might be in the form of U shaped or linear shaped. When the lamp is turned on the solid sodium gets heated thus it produces dim pink or red colored light and within few seconds when the sodium metal gets vaporized, the intensity of the light increases.
This type of lamps produces a virtually monochromatic light that is about the 589.3 nm wavelength. In fact two main spectral lines are very close together at 589.6 nm and 589.0 nm. Therefore the colors of the illuminated elements are not simply differentiated since they are seen almost completely by their reflection of this fine bandwidth yellow light. The low pressure sodium lamps have an outer glass vacuum cover around the inside light discharge tube for the thermal insulation that increases their efficiency.
The HPS lamps are quite smaller and include other elements like mercury. When the lamp is switch on a dark pink colored light will glow and when the sodium gets heated or warm, the light glows into a pinkish orange. Both the types of lamps are used in several places such as hotels, restaurants, cafes etc.