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125mm diameter plasma globe

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LAN_403

Mads Barnkob

Tue Sept 01 2009, 08:56PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

I bought a 125 mm clear light bulb for this little experiment and used the TL494 driver I am still writing about in the project section.

I took some pictures with the DSLR and recorded a HD movie, as I write it still processing at youtube. Read, look etc here:

There is one thing that go me wondering, the gas around the streamers are glowing green, my only reasonable guess would be that it is the gas mixture, as neither of the gasses normally used in light bulbs would emit green in their pure form.

Hon1nbo

Tue Sept 01 2009, 10:05PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

I have seen green glow in various bulbs I have used, but most notably in flashlight bulbs (then again, I didn't use the largest variety of bulbs so it could easily be in more sizes)

Frosty90

Wed Sept 02 2009, 09:51AM

Registered Member #1617 Joined: Fri Aug 01 2008, 07:31AM
Location: Adelaide, South Australia
Posts: 139

I've noticed a similar thing with standard 100w light globes too, except I didnt get green clouds, but pale pinky-yellow (skin colour is the closest thing that comes to mind). I was operating at about 5Mhz at the time, and the discharge would take a sort of hazy, cloud-like 'flame', that would persist for a short time (guessing 100 milliseconds or so) after power was removed. I couldnt get it to show up good on camera though. As for the green, It may be krypton; see here

about halfway down.

Cheers,
Jesse

Scott Fusare

Wed Sept 02 2009, 03:55PM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

I would guess that you are seeing the "after glow" of decaying metastable states. Both Argon and Nitrogen are prone to do this and both are likely present in the fill gas.

Plasma Lover

Wed Sept 02 2009, 05:24PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

It's also possible that the bulb you were using was under a slight vacuum and, thus, was generating gamma radiation, which appears green when passing through a glass envelope.

Scott Fusare

Wed Sept 02 2009, 05:46PM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

You are thinking of x-rays not gamma rays. If the pressure were low enough, say <100 mTorr, electrons might gain enough energy to cause the glass to fluoresce - which is what you are thinking of. In the process some x-rays are generated but they are not the cause of the glow.

That said, the pressure inside a standard incandescent lamp if far too high to generate x-rays.....

Plasma Lover

Wed Sept 02 2009, 08:04PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

scott fusare wrote ...

You are thinking of x-rays not gamma rays. If the pressure were low enough, say <100 mTorr, electrons might gain enough energy to cause the glass to fluoresce - which is what you are thinking of. In the process some x-rays are generated but they are not the cause of the glow.

That said, the pressure inside a standard incandescent lamp if far too high to generate x-rays.....

I wouldn't exactly say that a 12.5cm diameter lamp is standard. Also, if you look at the video you will notice how purple, translucent and energetic the 'streamers' are, which implies that it is low-pressure.

Also, here is a link to a wikipedia entry (with sources) that you should read: http://en.wikipedia.org/wiki/X-ray

Here's a quote from the formerly mentioned article:

"The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes had a longer wavelength than the radiation emitted by radioactive nuclei (gamma rays).[4] So older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10âˆ’11 m, defined as gamma rays.[5] However, as shorter wavelength continuous spectrum "X-ray" sources such as linear accelerators and longer wavelength "gamma ray" emitters were discovered, the wavelength bands largely overlapped. The two types of radiation are now usually defined by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus."

So, while Gamma Radiation and X-Radiation may not be the same exact thing, their frequencies do overlap and, thus, at some point they are the same thing.

GluD

Wed Sept 02 2009, 08:28PM

Registered Member #1221 Joined: Wed Jan 09 2008, 06:17PM
Location: Odense, Denmark
Posts: 196

I see you finally got yourself one of those awesome globes

Just about last chance anyhow since they banned them the 1st September..

I've notice a green glow in my own plasma globe (same bulb as you got) although not so clearly as in your photos.

Really nice photos indeed.

Scott Fusare

Wed Sept 02 2009, 09:28PM

Registered Member #531 Joined: Sat Feb 17 2007, 10:51AM
Location: Burlington, Vermont
Posts: 125

Several things -

While somewhat large at 12.5 cm, there is nothing particularly unusual about this incandescent lamp. They are commonly available in the hardware store, at least here in the NE USA. They are back filled with an Ar/N2 mixture at a pressure perhaps a bit below ambient. Some time spent with Google or perhaps one of those funny buildings full of books will help out here.

What makes you think that the properties of "purple, translucent and energetic" imply "low pressure"? For that matter, what are you considering "low pressure"? If the bulb were actually in the <100 mT pressure region there would be no defined streamers at all. This is strictly a higher pressure phenomenon. There are some great texts out there on gas discharge phenomenon. For a cheap but useful golden oldie try "Gaseous Conductors" by Cobine

I am well aware that the difference between "x-rays" and "gamma rays" is simply the electronic or nuclear origin (and in the limit, wavelength). If you were to dig a bit deeper you would find that the "green glow" phenomenon you are invoking is not due to X-Rays as the causal agent.

What is presented here is Argon/Nitrogen after glow and nothing more....

(Cranky Old Man climbing down off soapbox..)

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