mechanical make up of The High-Pressure Mercury Lamp

[JJWalecka]

I was reading about the mechanical make up of The High-Pressure Mercury Lamp. It describes the arc tube that contains a small amount of Argon gas that is used a conducting medium to facilitate the starting of the arc until the Mercury is vaporized. Once the discharge begins, the enclosed arc becomes a light source with one electrode acting as cathode and the other as an anode. The electrodes will exchange functions as the AC supply changes polarity.

My question: What is the definition of cathode and anode. I believe I know but I would like to have reference material to back up my theory.

Thank you for your time and effort.
Justin W

 

[LarryFine]

Re: mechanical make up of The High-Pressure Mercury Lamp

Anode: http://www.yourdictionary.com/ahd/a/a0320000.html

Cathode: http://www.yourdictionary.com/ahd/c/c0164200.html

 

[JJWalecka]

Re: mechanical make up of The High-Pressure Mercury Lamp

LarryFine thank you.

 

[mc5w]

Re: mechanical make up of The High-Pressure Mercury Lamp

There is also dry nitrogen or dry argon gas between the arc tube and the outer envelope. The filling pressure for this space in metal halide bulbs is 700 Torr, which is slightly less than atmospheric pressure. For reference atmospheric pressure is 760 Torr.

When the bulb heats up the gas between the arc tube and the outer envelope increases in pressure which transfers stress on the arc tube walls to the outer envelope. This keeps the arc tube from exploding because the heat weakens the arc tube glass.

If the arc tube somehow breaks or loses this gas the arc tube will tend to explode Real Soon Now.