High Pressure Mercury Lamp Quiz and Flashcards

What is the primary function of the choke in a high-pressure mercury lamp?

What is the purpose of the capacitor C in the circuit?

What is the typical pressure inside the arc tube after the mercury vapor is established?

What is the function of the auxiliary starting electrode S?

What is the duration of the operation to establish the mercury vapors and increase the pressure inside the arc tube?

What type of light is emitted by the mercury vapors in a high-pressure mercury lamp?

The arc tube is made of quartz and contains a small amount of mercury and argon gas.
The arc tube houses three electrodes: D, E (main electrodes), and S (auxiliary starting electrode).
Electrode S is connected through a high resistance R (about 50 kΩ) to the main electrode situated at the outer end of the tube.
When the supply is switched on, the initial discharge is established in the argon gas between D and S.
The initial discharge then spreads to the argon between D and E.
The heat produced due to the discharge through the gas is sufficient to vaporize mercury.
The pressure inside the arc tube increases to about one or two atmospheres in 5-7 minutes.
During this time, a discharge is established through the mercury vapors, which emit greenish-blue light.
A choke is used to limit the current drawn by the discharge tube to a safe limit.
A capacitor C helps to improve the power factor of the circuit.
Typical applications of high pressure mercury-vapour lamps include high-bay industrial lighting, flood-lighting, and street-lighting where high level illumination is required.