How does a discharge UV lamp works

In summary, the operational principle of a gas discharge lamp involves exciting rare gas atoms through collisions with free electrons, which are either produced through heating a filament (hot cathode) or through an initial high voltage (cold cathode). The atoms then release energy in the form of UV photons, which interact with the coating of the tube and emit visible light. The breakdown voltage needed to make atmospheric gas conductive is reduced in a vacuum and with certain gases, explaining why these gases are used in gas discharge lamps.
  • #1
poul
17
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I think i have looked at like 20-30 web pages, and i can't find a simple step-by-step explanation of the operational principle.

I know, that when a rare gas like Helium, relaxes from an excited state two characteristic emission lines occur. But how do you excite the gas in the first place?

I know you can excite it, by shooting some electrons through the gas, but we have no free electron in the system, since the electric field should not be strong enough to ionize the helium atom by itself.
 
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  • #2
There are free electrons in the system. The electrons get accelerated by the electric field. Once the electrons are a high enough kinetic energy, the atoms absorb a discrete quantity from them in an inelastic collision, becoming excited. The unstable, excited atoms quickly fall back to a lower state, emitting a UV photon in the process. This UV photon interacts with the coating of the tube in a similar manner, transferring energy to excited/ground states, emitting visible light.

I read your post again, and I am not sure what you mean. You have no free electrons in a system you are doing? I am not sure how that would work in this case. All gas discharge lamps I know of have free electrons flowing through an ionized gas.
 
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  • #3
The (electrons in the) atoms can also be excited through inter-atom collsions.
 
  • #4
TheFerruccio said:
There are free electrons in the system. The electrons get accelerated by the electric field. Once the electrons are a high enough kinetic energy, the atoms absorb a discrete quantity from them in an inelastic collision, becoming excited. The unstable, excited atoms quickly fall back to a lower state, emitting a UV photon in the process. This UV photon interacts with the coating of the tube in a similar manner, transferring energy to excited/ground states, emitting visible light.

I read your post again, and I am not sure what you mean. You have no free electrons in a system you are doing? I am not sure how that would work in this case. All gas discharge lamps I know of have free electrons flowing through an ionized gas.



okay so for a normal gas discharge lamp, we have free electrons you say. Are these made, by heating a filament or similar and then accelerated?
 
  • #5
poul said:
okay so for a normal gas discharge lamp, we have free electrons you say. Are these made, by heating a filament or similar and then accelerated?

It depends on if it is a hot cathode or a cold cathode. Hot cathode lamps use thermionic emission to release the electrons from the electrodes to maintain conduction in the gas. Cold cathodes need an initial (much higher than hot cathode) voltage to ionize the gas and make it conductive.

Atmospheric gas is typically non-conductive until this "breakdown voltage" is applied. The voltage necessary is reduced in a vacuum and with certain gases, which is why these lamps have the gases they do.
 

1. How does a discharge UV lamp produce UV light?

A discharge UV lamp works by passing an electrical current through a gas-filled tube, which causes the gas atoms to become excited and release energy in the form of UV light.

2. What type of gas is used in a discharge UV lamp?

Most discharge UV lamps use a combination of mercury vapor and an inert gas, such as argon or krypton, to produce UV light.

3. How does a discharge UV lamp differ from an incandescent light bulb?

Unlike incandescent light bulbs, which use a heated filament to produce light, a discharge UV lamp uses a gas-filled tube and does not produce visible light. Instead, it produces UV light, which is invisible to the human eye.

4. What is the wavelength range of UV light produced by a discharge UV lamp?

The wavelength range of UV light produced by a discharge UV lamp can vary depending on the specific gas mixture and design of the lamp. However, most commonly used discharge UV lamps produce UV light in the range of 254-365 nanometers.

5. How is a discharge UV lamp used in practical applications?

Discharge UV lamps have a wide range of practical applications, including sterilization, water and air purification, curing of inks and coatings, and detection of counterfeit money or documents. They are also used in medical and scientific research for DNA analysis and disinfection.

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