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What is Sodium Vapor Lamp? – Diagram, Working & Applications
A sodium vapor lamp is type of gas-discharge lamp that uses sodium (Na) in an exciting condition to produce light of thick blue color. The first sodium vapor lamp was commercially designed by Philips in 1932 in Holland.
Circuit Diagram of Sodium Vapor Lamp
The circuit diagram and the construction of a sodium vapor lamp is shown in the figure below.
As the sodium vapor lamp is a lamp of low luminosity, its length is large. To get the desired length, the sodium vapor lamp is made in the form of a U-tube. It has two oxide-coated electrodes which are sealed with the ends and the tube contains a little sodium and neon gas.
The U-tube is enclosed in a double walled vacuum flask to keep the temperature of the lamp within the working range. In general, a sodium vapor lamp operates at a temperature like 300 °C. In order to converse the heat generated and to ensure the lamp operating at normal temperatures, the discharge envelope is enclosed in a special vacuum envelope designed for this purpose.
Also, the circuit of the sodium vapor lamp consists a capacitor (C), a choke coil (L) and a small step down transformer. All these are connected in series with the sodium vapor lamp for heating the electrode to produce light.
Working of Sodium Vapor Lamp
When the sodium vapor lamp is turned on, it sends an electric discharge within the neon gas which generates sufficient heat to evaporate the solid sodium. In case, when the sodium vapor lamp is not operated, the sodium remains deposited on the side walls of the tube in solid condition.
Once the power supply is connected to the sodium vapor lamp, the neon gas is discharged and produces red-orange colored light. The heat generated by the discharge of the neon gas changes the solid sodium into sodium vapor. After few minutes, the sodium vapor lamp starts generating complete yellow colored light. The sodium vapor lamps are only suitable for AC supply and hence require choke control.
Advantages of Sodium Vapor Lamp
Following are the main advantages of using sodium vapor lamps −
Sodium vapor lamps have high efficiency.
They have comparatively longer life.
Heat produced by the sodium vapor lamps is very low.
Sodium vapor lamps are ideal for different applications.
These lamps are energy efficient.
Sodium vapor lamps work effectively in foggy and rainy season.
Disadvantages of Sodium Vapor Lamp
The disadvantages of sodium vapor lamps are as follows −
Sodium vapor lamps cannot be used in color identification areas.
Their power factor is very low, about 0.3 and hence require a capacitor to improve it.
They require an additional transformer.
Sodium vapor lamps need long tube so that they can give sufficient light output.
They require extra care in handling, because if it is broken and the sodium comes in contact with moisture fire will result.
They need 5 to 10 minutes to provide a complete light output.
Applications of Sodium Vapor Lamp
Some applications of the sodium vapor lamps are listed below −
Sodium vapor lamps are widely used for lighting in outdoor areas like roadways, parking lots, security areas, airports, goods yards, etc.
To provide lighting in industries, the high pressure sodium vapor lamps are used.
Sodium vapor lamps are also used for advertising purposes.
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