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Carbon Button Lamp Answered

The Nikola Tesla group forum is asking for new projects, so I'm posting this as a suggestion. I would love to build it myself, but I lack the tools and money. This is my first contribution to Instructables, so please comment constructively.

Nikola Tesla invented the Carbon Button lamp as a kind of incandescent light, because Thomas Edison banned him from using his incandescent filament bulbs. Nikola later discovered that versions of it could also be used in wireless, trans-Atlantic telegraphy, and to investigate what we now call x rays. In fact, he even used the lamp (or something similar to it) to take x-ray photographs, 8 years before Wilhelm Rotgen discovered them.
For this reason, I must warn you: this device may possibly generate x rays. I am not responsible for any harm of any kind that may or may not result from re-creating this interesting device.
There are phosphors that you can buy that will absorb x rays and re-emit them as visible light. I recommend that you coat the bulb with it until you know for sure that the x rays aren't strong enough to hurt you, or if makes x rays at all. Mixing it with a phosphor made for uv light wouldn't hurt either.

Theory of Operation:
The bulb is powered by a Tesla Coil, or other source of high voltage, high frequency current, such as a driver for a plasma globe (actually, the modern plasma globe is descended from this kind of technology!)
When the power is turned on, electricity bombards the carbon button. Because carbon isn't the best conductor, this causes the button to heat and release electrons into the bulb's vacuum (the technical name for this is "thermionic emission," or the "Edison effect") . These electrons, in turn, excite the remaining air molecules and cause them to create visible light. This is strikingly similar to how fluorescent lamps work!
Supposedly, the bulb should shine 10 times brighter than an incandescent bulb.
(Note that the excitation of the air molecules, not the incandescence of the button, is actually the main source of light from the bulb.)

If anyone decides to build it, please post an instructable showing the steps and finished product. I suggest you get started by reading the patent, number 514,170. You may also want to read part of Tesla's lecture, "Experiments with Alternate Currents of High Potential and High Frequency."

To anyone who will attempt this, I wish you good luck!


A few questions:

Can a joule thief produce a high enough voltage to drive this type of lamp, or is a Tesla coil necessary?

Is the loss of material from the carbon button the same effect as the "sputter" that makes regular fluorescent lamps burn out?

If the lamp's gas were mercury, instead of low pressure air, and the glass had a phosphor coating, would it's efficiency be the same as that of a conventional fluorescent lamp?

How does a single electrode manage to heat up the carbon button?

On second thought, scratch my answer to your second question. In short, I'm pretty sure this effect is not what makes fluorescent bulbs burn out.

A Tesla coil or any other kind of high-frequency HV AC power supply would be necessary; this kind of bulb not only needs high voltages but also high frequencies.

If I'm understanding what you're asking, I suppose this effect is similar to how fluorescent bulbs heat their filaments; pretty sure it's not what makes them burn out.

That last one is a good question; I don't know, as I've never actually seen one function. Potentially, yes.

And a single electrode heats the carbon button by making it ionize the air around it in the globe.

Hope that helps :)

It's a plasma-globe? L (please don't use capitals for emphasis)

Sorry about the capitals.

No, technically it is not a plasma globe (but, for the record, Tesla invented that to, as the "inert gas discharge tube." Some other guy came up with the modern versions.)
Plasma globes are filled with very low pressure inert gasses, usually a mix of neon and argon. These inert gasses are what give the streamers the color. The carbon button lamp is filled with very very low pressure air, and produces a white light (during the first few minutes of operation, however, the carbon button lamp will produce brushes like modern plasma globes, as show in the below drawing from Tesla's lecture. They go away very quickly.)
But the main difference is the carbon electrode. Unlike a plasma globe, which uses a conductive electrode inside a glass stem, the button extends out of the glass stem and, because it is a bad conductor, burns the way that the rod in an old carbon arc lamp will burn.

Do you know how I can put this topic on the Tesla group's page?


So the carbon burns for a while?
I don't add things to groups, so I can't help you on that question.
Someone around here wanted some neon - they were looking at making lights - I'll see if I can find 'em...


I don't think the carbon burns, Lemonie. The globe is pumped down to vacuum. It sounds to me like it's just the residual molecules (probably far too few to actually burn a "chunk" of carbon) which get ionized by the corona discharge from the carbon. Those ionized molecules recombine and emit visible light. As the original poster said, it's essentially the same process as in a fluorescent tube, but without the opaque phosphor coating.

I was going from The carbon button lamp is filled with very very low pressure air, and produces a white light (during the first few minutes of operation. Otherwise it seems to be a plasma globe to me. Fluorescent tubes have a pressure of mercury in them, this is not the same.


They do, but it's also quite low pressure. I'm thinking in terms of turn-of-the-century vacuum technology; Tesla could probably get down to 10-5 Torr or so, but nowhere near the 10-10 we get today with TMPs (mmm....turbo salad).

I love that sort of thing. But probably the best bit of kit I ever touched was only a 500MHz NMR spectrometer... L

The low pressure mercury vapor-argon in fluorescent tubes creates ultraviolet light, which is absorbed by the phosphor coating and re-emitted as visible light (unless it's a germicidal tube, shown below.) In the carbon button lamp, visible light is produced without the phosphor coating, although as I said, there may be some ultraviolet light and x rays.

My bad, "burn" was the wrong word for me to use. I'll fix that. But is does get white hot. I'm a little bit unsure about how the lamp operates. The theory I posted here came from an excerpt from "Tesla: Man out of Time;" search Carbon Button Lamp on Google and you'll find it.

Thanks for the advice, but no neon is needed for the lamp. He mentioned a vaccum pump in one of his posts; I'll take a better look at it later. Thanks again.

It looked like he was working with glass, vacuum and high voltages (and is in the high voltage group and Nikola Tesla group, amongst others) L

You asked, "Do you know how I can put this topic on the Tesla group's page?" You can't. If you had gone to that group in the first place and selected the [New Topic] link from their forum, this topic would have been assigned there automatically. The I'bles Web scripts don't have any interface (neither for members or even for Staff) for putting an existing forum topic into a group. The best you can do is to create a topic over there with a link to this one, but that's not a great solution, I know.