What is Mercury Vapor Lamp : Construction and Its Working

A lamp is a device that illuminates a light on supplying electric current. There are different types of electrical lamps they are, incandescent, mercury, sodium, CLF, LED lamps. The mercury vapor lamp was invented in the year 1901 by Peter (New York). This is a high-intensity discharge lamp that is commercially available and is designed to overcome the disadvantage of fluorescent lamps (which is a cold-sensitive lamp). The main advantage of this lamp is that it produces bright white light with a long rated life of 24000 hours. The day to day application of this lamp can be observed is a street light.

What is Mercury Vapor Lamp?

Definition: A lamp that consists of vaporized mercury to generate light by using an electric arc is known as a mercury vapor lamp. Basically, this lamp discharges gas when heated or cooled. The mercury which is present inside the tube is in liquid form (at room temperature) which is ionized before generating light. Its wavelength at low pressure ranges between 184 nm and 253 nm.

This is one kind of hot cathode discharge lamp with mercury vapour hence

it is known as mercury vapour lamp.

Construction :

It consists of evaluated glass bulb with another hard evacuated glass tube.

Two tungusten filaments are placed at upper and lower end of glass tube. A

starting electrode with high starting resiatance in series 8 placed near the 

upper flament. Normally screw cap is provided for holding lamp in the bo

An argon gas with low pressure with small quanuty of mercury is lled in

tube. Figure shows the constructional details.

Working

The high pressure mercury lamp is connected to A.C. supply through choke   .  

having different tappings. Required high voltage at the starting is provided

the upper main electrode and starting electrode which discharge the gas a

provide the path for the flow of electron between upper and lower main electrode  and  starting  electrode  which  discharge  the gas and  provide  the path for the  flow  if electron between  upper and  lower  main electrode 

with yellow- bluc light at the starting. After complete discharge of gas an

evaporation of mercury, the lamp gives white-bluish light. This lamp takes

to 5 minutes to give full illumination. The high pressure mercury vapour lan

works property in the following conditions.

(1) It can only be instailed in vertical position.

(2) It can work only on A.C. Supply

(3) It takes some time for giving full light.

(4) The voltage of lamp and choke must be same.

Choke: The function of choke is to provide required high voltage during

starting and stabilize normal voltage after full glowing of lamp.

Applications:

(1) This lamp is available in the ratings of 80 W. 125 W, 250 W 400 W

and 1000 W.

(2) It is used for street lighting and decoration purpose etc.

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