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.

Lamp Construction

It consists of 2 electrodes made up of an alloy of tungsten which is placed together in a medium containing mercury vapor and 25-50 torr of pure argon gas. These electrodes are enclosed in an elliptically shaped glass tube made up of silica.


The external circuit connections from the bulb are given to the following components

  • A Ballast component is similar to a transformer with high leakage reactance. It consists of 4 connecting ports like “Com, 240 V, 200 V, IGN”
  • An Ignitor which consists of three ports like red, yellow and black
  • It  consists of 2 polarity pins for connection
  • The main purpose of the ballast and ignitor is to control voltage and current.

The ballast port connection is made as follows,

  • Com port is connected to one terminal of the lamp, 240V port is connected to the 200V phase directly, 200V of ballast is connected to the yellow port of ignitor, and the IGN port is connected to the red port of ignitor.
  • The black terminal of an ignitor is connected to the neutral phase and also to the other terminal of the lamp.

Working of Mercury Vapor Lamp

The mercury vapor and neon gas (pink in color) present in the bulb requires high voltage at the starting to illuminate light. When high voltage is applied, we can observe that the neon gas which was originally in pink color will change into orange color by heating. It is similar to a 100-watt glowing bulb and it takes 5 to 7 minutes to turn on completely.


The ignitor which is present internally consists of a bimetallic strip and capacitor, which provides high starting voltage. When the bimetallic strip expands on heating, it will short-circuit then the lamp will be turned ON. When this bimetallic strip cools, it disconnects the connection and turns off the lamp. Hence by connecting the ballast and ignitor to this lamp, the mercury vapor and neon gas get heated up and expands the bulb inside to illuminate the light.



The advantages of the mercury vapor lamp include the following.

  • They are energy efficient (35 to 65 lumens/watts)
  • Rated life of 24,000 hrs
  • The output is clear white light
  • It provides with high intensity
  • It can be available in different colors, shapes, sizes, and ratings.


The disadvantages of the mercury vapor lamp include the following.

  • Maintenance of lumen is poor
  • It takes 5 to 7 minutes warmup before fully glowing the bulb
  • The cooling time is 5 to 6 minutes
  • They are voltage sensitive

Applications of Mercury Vapor Lamp

The applications are

  • Industrial areas
  • Street lights
  • Security
  • Stairwells
  • Home appliances like garages.


1). Are Mercury Vapour lamps dangerous?

Yes, these lamps are dangerous to human life when there is a leakage is in the larger amount.

2). Which gas is used in a mercury vapor lamp?

They filled with a portion of mercury vapor and 25-50 torr of Argon gas.

3). What are the main components of the Mercury vapor lamp?

The 3 main components are

  • Ballast/transformer which is high leakage reactance transformer
  • Ignitor
  • It comprises of mercury vapor and argon gas.

4). Why mercury is used in lamps?

In order to provide greater efficiency of energy and longer rated life

5). What is the purpose of Ballast and ignitor in the mercury-vapor lamp?

The main purpose of ballast and ignitor is control voltage and current.

6). What is the span rate of the mercury vapor lamp?

The span rate of the lamp is 24,000 hours.

7). What is the range of MV – lamp?

Its wavelength at low pressure ranges between 184 nm and 253 nm.

Thus, this is all about an overview of the mercury vapor lamp. A lamp emits luminous light on supplying electric current. There are different types of lamps like an incandescent lamp, sodium vapor lamps, CLF, LED lamps. This is is a high-intensity discharge lamp with more energy efficiency. It is covered with a glass which is elliptically shaped and is filled with mercury vapor and pure neon gas, ballast and ignitor which is present are used to control voltage and current of the lamp. It requires at least 5 to 7 minutes to illuminate light and 5 to 6 minutes to cool down. Usually, it works up to 24,000 hours. The main advantage is that it is energy efficient.