Sodium Vapour Lamp

Sodium Vapour Lamp consists of a discharge tube created from a heat resistant glass, containing a small amount of metallic sodium, neon gas and two electrodes, Neon gas is added to commence the discharge and to create sufficient heat to vaporize the sodium. Because of law pressure inside the tube, a sufficiently extended tube essential to acquire far more light. To decrease the overall dimension of the lamp, this tube is usually bent into U-shape.

The light produced by this lamp is yellowish which is made at its optimum pressure of chicken coops and runs about .004mm of mercury. This pressure is obtained at a temperature of about 280 C website and so it becomes necessary to sustain this temperature. For this objective the U-tube is enclosed in a double walled flask to avoid lose of heat. The double walled flask is interchangeable and can be fitted on to yet another U-tube. Although replacing the inner U-tube one particular should be quite cautious due to the fact if it is broken and sodium comes in make contact with with moisture, it could result in fire.

All electric discharge lamps require a larger voltage at the time of beginning and low voltage throughout operation. Usually, sodium vapour lamps are operated by a high leakage reactance transformer. At beginning a high voltage of about 450 volts is applied across the lamp which is adequate to begin the discharge. When the lamp is totally operative immediately after ten - 15 minutes, the voltage across it falls to about 150 volts. Simply because of the high reactance of circuit, the power issue is low and therefore a p.f improvement capacitor is connected.

The efficiency of a low pressure sodium vapour lamp is very high (about 40 - 50 lumens/watt) and it produces a light of powered by specific wavelength getting yellow color. Sodium lamps are mostly employed for street, high way and airfield lighting where color distinction is not so needed.