Sodium Vapour Lamp

出典: くみこみックス

Sodium Vapour Lamp consists of a discharge tube produced from a heat resistant glass, containing a modest amount of metallic sodium, neon gas and two electrodes, Neon gas is added to start the discharge and to create enough heat to vaporize the sodium. Because of law pressure inside the tube, a sufficiently extended tube required to acquire a lot more light. To decrease the overall dimension of the lamp, this tube is usually 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 essential to retain this temperature. For this goal the U-tube is enclosed in a double walled flask to stop lose of heat. The double walled flask is interchangeable and can be fitted on to an additional U-tube. Although replacing the inner U-tube one particular should be very cautious image because if it is broken and sodium comes in make contact with with moisture, it might outcome in fire.

All electric discharge lamps need a higher voltage at the time of starting and low voltage throughout 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 commence the discharge. When the lamp is totally operative immediately after 10 - 15 minutes, the voltage across it falls to about 150 volts. Due to the fact tour backyard chicken coop of the high reactance of circuit, the power aspect is low and therefore a p.f improvement capacitor is connected.

The efficiency of a low pressure sodium vapour lamp is very high (about tumbshots 40 - 50 lumens/watt) and it produces a light of particular wavelength possessing yellow color. Sodium lamps are mostly employed for street, high way and airfield lighting where color distinction is not so essential.