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Sodium Vapour Lamp consists of a discharge tube created from a heat resistant glass, containing a tiny 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. Due to the fact of law pressure inside the tube, a sufficiently long tube needed to obtain more light. To decrease the all round dimension of the lamp, this tube is generally bent into U-shape.

The light produced by this lamp is yellowish which is produced at its optimum pressure of about .004mm of mercury. This pressure is obtained at a temperature of about 280 C and so it becomes needed to maintain this temperature. For this purpose the U-tube is enclosed in a double walled flask to avoid shed of heat. The double walled flask is interchangeable and can be fitted on to another U-tube. While replacing the inner U-tube one must be really cautious due to the fact if it is broken and sodium comes in speak to with moisture, it may result in fire.

All electric discharge lamps demand a higher voltage at the time of starting and low voltage in the course of operation. Generally, 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 start the discharge. When the lamp is fully operative after 10 - 15 minutes, the voltage across it falls to about 150 volts. Since of the high reactance of circuit, the energy element 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 distinct wavelength obtaining yellow color. Sodium lamps are mainly employed for street, high way and airfield lighting where color distinction is not so needed. reviews electronic cigarettes via here's the site