Sodium Vapour Lamp

Sodium Vapour Lamp consists of a discharge tube created from a heat resistant glass, containing a small 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. Due to the fact of law pressure inside the tube, a sufficiently long tube required to acquire a lot more light. To reduce the overall dimension of the lamp, this tube is generally bent into U-shape.

The light developed by this lamp is yellowish which is developed at its optimum pressure of about .004mm of mercury. This pressure is obtained at a temperature of about 280 C and division so it becomes needed to keep this temperature. For this objective the U-tube is enclosed in a double walled flask to avert shed of heat. The double walled flask is interchangeable and can be fitted on to an additional U-tube. While replacing the inner U-tube 1 have to be extremely cautious simply because advertisers if it is broken and sodium comes in contact with moisture, it might outcome in fire.

All electric discharge lamps demand a greater 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 principles is applied across the lamp which is enough to start the discharge. When the lamp is totally operative following 10 - 15 minutes, the voltage across it falls to about 150 volts. Since of the high reactance of circuit, the energy 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 possessing yellow color. Sodium lamps are mainly employed for street, high way and airfield lighting exactly where color distinction is not so necessary.