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出典: くみこみックス

Sodium Vapour Lamp consists of a discharge tube created from a heat resistant glass, containing a small quantity of metallic sodium, neon gas and two electrodes, Neon gas is added to start the discharge and to develop sufficient heat to vaporize the sodium. Because of law pressure inside the tube, a sufficiently lengthy tube required to acquire more light. To lessen the overall dimension of the lamp, this tube is generally bent into U-shape. The light produced by this lamp is yellowish which is created 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 preserve this temperature. For this purpose the U-tube is enclosed in a double walled flask to stop shed of heat. The double walled flask is interchangeable and can be fitted on to an additional U-tube. Although replacing the inner U-tube 1 have to be quite careful because if it is broken and sodium comes in speak to with moisture, it might result in fire. All electric discharge lamps demand a higher voltage at the time of beginning and low voltage throughout operation. Typically, sodium vapour lamps are operated by a high leakage reactance transformer. At starting a high voltage of about 450 volts is applied across the lamp which is sufficient to start the discharge. When the lamp is completely operative immediately after ten - 15 minutes, the voltage across it falls to about 150 volts. Because of the high reactance of circuit, the power factor is low and therefore a p.f improvement capacitor is connected. The efficiency of a low pressure sodium vapour lamp is quite high (about 40 - 50 lumens/watt) and it produces a light of particular wavelength having yellow color. Sodium lamps are mainly employed for street, high way and airfield lighting where color distinction is not so necessary. chicken coups