Sodium Vapour Lamp

出典: くみこみックス

Sodium Vapour Lamp consists of a discharge tube made from a heat resistant glass, containing a modest amount of metallic sodium, neon gas and two electrodes, Neon gas is added to commence the discharge and to develop sufficient heat to vaporize the sodium. Since of law pressure inside the tube, a sufficiently long smokestik tube required to obtain much more light. To lessen the all round dimension of the lamp, this tube is generally bent into U-shape.

The light developed 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 essential to maintain this temperature. For this objective the U-tube is enclosed in a double walled flask to avert lose of heat. The double walled flask is interchangeable and can be fitted on to another U-tube. Even though replacing the inner U-tube a single need to be quite cautious simply because if it is broken and sodium comes in contact with moisture, it may outcome in fire.

All electric discharge lamps demand a higher voltage at the time of beginning and low voltage during operation. Typically, 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 begin the discharge. When the lamp is fully operative immediately after 10 - 15 minutes, the voltage across it falls to about 150 volts. Due to the fact of the high reactance of circuit, the energy issue is low and hence a p.f improvement capacitor is connected.

The efficiency of a low pressure like i said sodium vapour lamp is quite high (about 40 - 50 lumens/watt) and it produces a light of blu e cig specific wavelength obtaining yellow color. Sodium lamps are mainly employed for street, high way and airfield lighting exactly where color distinction is not so essential.