Sodium Vapour Lamp

Sodium Vapour Lamp consists of a discharge tube made 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 enough heat to vaporize the sodium. Simply because of law pressure inside the tube, a sufficiently long tube necessary to acquire much more small blue arrow light. To reduce the general dimension of the lamp, this close window tube is usually bent into U-shape.

The light created 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 required to preserve 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 one more U-tube. Whilst replacing the inner U-tube one particular should be really careful since if it is broken and sodium comes in get in touch with with moisture, it may outcome in fire.

All electric discharge lamps call for like a higher voltage at the time of starting and low voltage during operation. Normally, 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 sufficient to commence the discharge. When the lamp is fully operative right after ten - 15 minutes, the voltage across it falls to about 150 volts. Since of the high reactance of circuit, the power issue 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 distinct wavelength obtaining yellow color. Sodium lamps are mainly employed for street, high way and airfield lighting exactly where color distinction is not so needed.