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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 sufficient heat to vaporize the sodium. Due to the fact of law pressure inside the tube, a sufficiently extended tube essential to obtain more light. To minimize the overall dimension of the lamp, this tube is typically bent into U-shape.

The light created 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 preserve this temperature. For this goal the U-tube is enclosed in a double walled flask to prevent lose of heat. The double walled flask is interchangeable and can be fitted on to an additional U-tube. Even though replacing the inner U-tube 1 need to be extremely cautious simply because if it is broken and sodium comes in make contact with with moisture, it may result in fire.

All electric discharge lamps require a larger voltage at the time of beginning and low voltage in the course of 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 begin the discharge. When the lamp is fully operative following 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 extremely high chicken houses (about 40 - 50 lumens/watt) and it produces a light of particular wavelength obtaining yellow color. Sodium lamps are mainly employed for street, high way and airfield lighting exactly where color distinction is not so necessary.