Sodium Vapour Lamp

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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 start off the discharge and to develop adequate heat to vaporize the sodium. Simply because of law pressure inside the tube, a sufficiently long tube essential chicken houses to acquire far more light. To decrease the general dimension of the lamp, this tube is normally bent into U-shape.

The light created 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 necessary to sustain this temperature. For this goal the U-tube is enclosed in a double walled flask to prevent shed of heat. The double walled flask is interchangeable and can be fitted on to yet another U-tube. While replacing the inner U-tube one particular have to be quite cautious because if it is broken and sodium comes in make contact with with moisture, it may outcome in fire.

All electric discharge lamps call for a larger voltage at the time of starting and low voltage throughout operation. Generally, 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 enough to begin the discharge. When the lamp is totally operative after 10 - 15 minutes, the voltage across it falls to about 150 volts. Due to the fact of the high reactance of circuit, the power element is low and therefore 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 certain wavelength obtaining yellow color. Sodium lamps are primarily employed for street, high way and airfield lighting exactly where color distinction is not so needed.