Re: Help on how a Tesla coil excites a neon bulb
hen918, Wed Sept 02 2015, 05:40PM

The air and the glass of the non acts a capacitor, the "Tesla coil" a high frequency high voltage source (with a huge electric field) and the neon is the load.
The tesla coil is sending out a hell of a lot of electrons. Some of these are energising your neon.
The more complex answer involves capacitive coupling (the air is the dielectric of the capacitor)

Re: Help on how a Tesla coil excites a neon bulb
TeslaIsBae, Wed Sept 02 2015, 06:03PM

Thanks, that makes sense how the air and the glass of the bulb act as capacitors that then discharge into the neon gas, the load. So if I understand it correctly, by the "energising neon"you mean the Tesla coil's electric field pushes electrons into the neon bulb? Those then ionise the neon gas, which releases free electrons, excites them and the process is then that of a normal neon bulb.

Re: Help on how a Tesla coil excites a neon bulb
hen918, Wed Sept 02 2015, 07:05PM


Umm, yes, basically... The only difference between using the neon normally and with a tesla is that usually you use wire to conduct the voltage, not air! Neons only need very small currents to light which is what lets them light through the ionised air around them.

Re: Help on how a Tesla coil excites a neon bulb
TeslaIsBae, Wed Sept 02 2015, 07:20PM

Perfect, thank you very much. Sorry for sounding so primitive sometimes; I still have a lot to learn :)

Re: Help on how a Tesla coil excites a neon bulb
Antonio, Wed Sept 02 2015, 09:26PM

The Tesla coil does not have to push electrons against the tube (what it would do only if actually sparking to the tube). It produces an intense electric field around it, and the low-pressure gas inside the tube gets ionized just due to this, without need of an external power source connected through wires.

Re: Help on how a Tesla coil excites a neon bulb
TeslaIsBae, Thu Sept 03 2015, 02:14AM

I've noticed that the bulb shines extremely bright when there is a spark constantly jumping to it, but it gets dimmer when it is just being excited by the electric field. Is the process that light the bulb up the same when there is a spark jumping to it and when there isn't? Is it simply that a lot more electrons are discharged into the neon bulb when a spark jumps to it?

Re: Help on how a Tesla coil excites a neon bulb
dexter, Thu Sept 03 2015, 06:31AM

i don't like this "the intense electric field ionize the neon" i want more i want to know how
Could it be due to the low pressure neon having a lower resistance than air thus developing a potential difference between different regions of the glass placed at different lengths from the source of the electric field (inverse square drop with distance of the value of the field in different points)?

this explains why a neon lights up even when isolated from ground or other objects?

Re: Help on how a Tesla coil excites a neon bulb
Dr. Slack, Thu Sept 03 2015, 07:50AM

There are two completely separable issues here. How a neon bulb lights when connected by wires to a power source, which is an interesting enough problem in its own right, and how a TC gets power to it through the air.

Which does the OP want to know about? If both, let's deal with them one at a time, using the most appropriate description for each. The neon will need electric fields, electrons, ions. Power through the air is better handled with just electric fields, capacitance, displacement current. If an arc jumps TC to neon, then we're back to electrons and ions again.

Re: Help on how a Tesla coil excites a neon bulb
Uspring, Thu Sept 03 2015, 10:04AM

The low pressure in the neon tube will make the gas inside it conductive at much lower electric field strength than necessary e.g. in the air surrounding it. It can therefore light up at distances far outside the reach of arcs of the coil. So why doesn't the tube light up near a high voltage DC source like a van de Graaff generator?

Say you have a VDG charged up to a high positive voltage. Then the electrons inside the tube will be pulled towards the VDG and the positive ions repelled from it. That will cause a field inside the tube against the direction of the VDG field. So there will be no field in the tube and no light.

A Tesla coil produces a high frequency AC field. That causes a permanent flow of electrons and ions back and forth between the sides of the tube facing the coil and opposite from it. The tube will light up.

If an arc hits the tube, there is a conductive path from the TC to the tube, which causes the high electric field of the TC top to be transported into the vicinity of the tube. The tube will be much brighter then.

Re: Help on how a Tesla coil excites a neon bulb
Ash Small, Thu Sept 03 2015, 10:07AM

Gases like neon and argon are much easier to ionise than gases like oxygen and nitrogen (air), and at resuced pressure are again even easier to ionise (see Paschen curves for more detail).

When placed in an electric field, the neon ionises due to 'capacitive coupling', rather than 'inductive coupling' (at least, this is the conventional thinking. I think TC's are capable of inducing currents as well as the secondary winding is an inductor, so maybe it's not so clear cut, but it's generally accepted that it's capacitive coupling that does all the work here.)

Generally, with capacitively inducted plasmas, the atoms of neon (in this case) are pulled apart by the rising electric field, with electrons pulled in one direction, and Ne+ ions pulled in the other direction. These ions and electrons can collide with more neon atoms to create more ions. When the field reverses they are pulled in the other direction. The light is produced as neon ions and electrons re-combine to produce atoms again, When this happens a photon is released.

Inductively coupled plasmas, on the other hand, tend to cause the ions and electrons to move in circles or spirals, first in one direction, then in the other.

Basically, as the voltage on the topload rises the electrons in the neon bulb are attracted to the topload and the positive ions repelled. As the voltage on the topload reverses, the electrons are repelled and the ions are attracted, and light is emitted as these ions and electrons re-combine, producing photons.

I hope I got it all 'the right way round', I've at least supplied a few other terms for you to google

EDIT: Looks like Udo posted while I was writing.

Re: Help on how a Tesla coil excites a neon bulb
TeslaIsBae, Fri Sept 04 2015, 08:30AM

Thank you guys, it still took me quite a while to understand everything even with your great explanations. But I would just like to confirm what I understand:

So a neon bulb is always excited through capacitive coupling, no matter if it has an electric arc jumping to it or if it's further back in the electric field of the TC. The only difference is that the electric arc ?

Thanks

Re: Help on how a Tesla coil excites a neon bulb
Uspring, Fri Sept 04 2015, 09:55AM

TeslaIsBae wrote:

So a neon bulb is always excited through capacitive coupling, no matter if it has an electric arc jumping to it or if it's further back in the electric field of the TC. The only difference is that the electric arc

Uspring wrote ...
causes the high electric field of the TC top to be transported into the vicinity of the tube.

?

Yes, and the field drops off at larger distances from the TC top. At sufficiently large distances the neon bulb will stop emitting light.
I should have said more accurately, that the charge of the top of the TC is transported near to the bulb, if an arc hits it. The charge of the top is causing the field and a conductive path like an arc will transport it close to the bulb increasing the field there.

If the other side of the tube is grounded, you'll have a direct current path from the top through the tube to ground. In this case capacitive effects are negligible and the tube will become very bright.

Re: Help on how a Tesla coil excites a neon bulb
TeslaIsBae, Fri Sept 04 2015, 10:21AM

Ok, that answers all my question, for now Thank you everyone!

Re: Help on how a Tesla coil excites a neon bulb
dexter, Wed Sept 09 2015, 05:53PM

well this is interesting



also works with the LED floating in the air

Re: Help on how a Tesla coil excites a neon bulb
Ash Small, Wed Sept 09 2015, 06:20PM


I know it's still a bit early, but wireless Xmas tree lights, maybe?

Re: Help on how a Tesla coil excites a neon bulb
E.TexasTesla, Fri Nov 20 2015, 03:35AM

I placed a small laser pointer on top of my toroid once and the laser diode fired right up.
It only worked for a short time so I'm not sure what was actually going on.

Re: Help on how a Tesla coil excites a neon bulb
Art, Mon Jan 04 2016, 04:14PM

When a coil illuminates a bulb you’re holding it’s because a circuit is completed through the bulb, continuing through your body (mainly the surface of your skin), which is also capacitively coupled to ground. When this is happening, the bulb and your body is the path of least resistance (or in this case impedance) to ground. If you want to take your body out of the equation, you can do so by connecting one side of the bulb to some foil sheet sitting on the ground, and suspending the bulb near the coil.

Re: Help on how a Tesla coil excites a neon bulb
TwirlyWhirly555, Mon Jan 04 2016, 07:14PM

i tried it with a Bunch of neons on a pice of 5mm acrylic sitting on top of a SSTC @ 24V halfbridge

IMG_0683[1] by TwirlyWhirly555, on Flickr

Re: Help on how a Tesla coil excites a neon bulb
Perezx, Tue Jan 05 2016, 05:45AM

Guys, thats just a radio transmission. If your neon tube has any electrodes - they work like antennas. If not - gas itself, especially when ionised, is conductive.
Try to touch one electrode by hand (which means grounding) or attach a wire (antennae) to it - bulb will ligh up brighter / on a longer distance.
Spark between bulb and coil acts like a wire.
LED acts like a rectifier, its terminals - like antennas.