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Sodium Vapour Lamp consists of a discharge tube produced from a heat resistant glass, containing a little amount of metallic sodium, neon gas and two electrodes, Neon gas is added to begin the discharge and to create enough heat to vaporize the sodium. Because of law pressure inside the tube, a sufficiently long tube essential to acquire more light. To decrease the overall dimension of the lamp, this tube is typically bent into U-shape. The light created by this lamp is yellowish which is produced at its optimum stress of about .004mm of mercury. This pressure is obtained at a temperature of about 280 C and so it becomes essential to keep this temperature. For this purpose the U-tube is enclosed in a double walled flask to prevent lose of heat. The double walled flask is interchangeable and can be fitted on to another U-tube. Although replacing the inner U-tube a single must be extremely cautious due to the fact if it is broken and sodium comes in contact with moisture, it may outcome in fire. All electric discharge lamps need a larger voltage at the time of starting and low voltage during operation. Learn new resources on a related web resource - Click here:  [http://blog.yam.com/dollarcork95/article/68573890 dollarcork95 's blog: For Wonderful Body, Acquire European Steroids Testosterone! - y] . Generally, sodium vapour lamps are operated by a high leakage reactance transformer. At starting a higher voltage of about 450 volts is applied across the lamp which is sufficient to begin the discharge. When the lamp is completely operative following 10 - 15 minutes, the voltage across it falls to about 150 volts. Simply because of the high reactance of circuit, the energy element is low and hence a p.f improvement capacitor is connected. The efficiency of a low pressure sodium vapour lamp is really high (about 40 - 50 lumens/watt) and it produces a light of particular wavelength having yellow color. Sodium lamps are mostly employed for street, higher way and airfield lighting where colour distinction is not so essential.