Sodium Vapour Lamp

Sodium Vapour Lamp consists of a discharge tube produced from a heat resistant glass, containing a small amount of metallic sodium, neon gas and two electrodes, Neon gas is added to start off the discharge and to create enough heat to vaporize the sodium. Since of law pressure inside the tube, a sufficiently lengthy tube needed 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 made at its optimum pressure of about .004mm of mercury. This pressure is obtained at a temperature of about 280 C and so it becomes required to retain this temperature. For this purpose the U-tube is enclosed in a double walled flask to partner site prevent lose of heat. The double walled flask is interchangeable and can be fitted on to an additional U-tube. Whilst replacing the inner U-tube one should be really careful simply because if it is broken and sodium comes in get in touch with with moisture, it may possibly result in fire.

All electric discharge lamps call for a larger voltage at the time of starting and low voltage during 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 adequate to start off the discharge. When the return to site lamp is fully operative immediately after 10 - 15 minutes, the voltage across it falls to about 150 volts. Because of the high reactance chickencoop of circuit, the power 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 specific wavelength having yellow color. Sodium lamps are primarily employed for street, high way and airfield lighting where color distinction is not so necessary.