Cathode Trivia(no cheating)

[AKA_RA]

Without looking it up, does anyone know why cold cathodes are refered to as such? I only pose this question because I thought I knew, and I was actually quite wrong(not uncommon, :D ).

[Cevinzol]

I'm assuming a cold cathode doesn't pre-ionize the fluorescing elemental media.

If you watch a mercury vapor streetlight turn on you will notice that it takes several minutes for the light to brighten up. I'm guessing a cold cathode works similar to the instant on compact fluorescent light bulbs used to replace incandescent bulbs.

[AKA_RA]

i think compact fluorescent lights are considered cold, but not all fluorescent lights are cold, so i guess it could be either. if you cant tell i am be no means an expert in this field. im really not sure about street lights though, since i dont know what specific type of bulb they use. they must use the same type of lights in my old church gym, they used to bug the hell out of me as the lights "warmed up." i believe both the CFL and whatever the street lights are use mercury vapors and either neon or argon gas. since this is the standard process used to produce the UV light required to excite the phosphor in the bulbs.
although im unsure of is what you meant by "pre-ionize," i think you got it right. but depending on what it was you meant exactly, you could be right or wrong. but hell, its close enough for me.
since hot cathodes use a heat source, such as a filement, theyre considered hot. and since cold cathodes do not induce a heat sorce to get a reaction and instead rely on field emission, as opposed to thermionic(thats the word, right?) emission.
im actually curious now, the differance between the little CFL bulbs and the ones they use in street lights. the ones in street lights may be hot, not cold, since they seem to emit more light, and thats one of the characteristics of hot cathodes.
anyways, to show how educated i was on the matter when i first heard of cold cathode lighting, i was under the impression that it had more to do with the actual temperature of the lamp. and thats why people were using them in computer cases, instead of using neon lighting. i look back and laugh at myself now. this kinda talk makes me wanna take physics all over again.

[Exley]

I think i read somewhere that they got the name because they start cold.

[GUI]

Cold cathodes don't have a heating element on the cathode.

[Slug Toy]

speaking from an overly complicated point of view, i think it has something to do with population inversion, and the strength at which this happens. seems to me flourescents and cold cathodes work on the same principle as lasers (you run a fairly large charge perpendicular to the direction of light output). basically, the light you see is the product of the gasses inside being excited to a higher energy state, and emitting a photon when they crash back down.

so why would i go through that explanation? because there are different power levels depending on how much energy you put in. some heat beams (infrared lasers) that ive made are strong enough to cut steel, but they run on upwards ot 100 000 volts, and have huge capacitor banks, and to say the least they DO heat up (if you're not careful they basically self destruct). flourescent lights and cold cathodes only run on a fraction of that. i think my brother took apart a cold cathode transformer and found that it was putting out about 4000 volts. 100 000 versus 4000 is a large difference. im not sure how much less heat 4000 volts equates to (dont have my thermodynamics stuff out), but i think its safe to say a LOT less.

so is that accurate?

[Slug Toy]

I'm assuming a cold cathode doesn't pre-ionize the fluorescing elemental media.

i just couldnt resist correcting this. i tried, but couldnt... perhaps you were thinking of charged particles.

the media doesnt really ionize. most, if not all, of these devices use noble gasses and perhaps mercury. noble gasses are stable, and do not ionize under these conditions (they use krypton for ion thrusters in space because the method used can strip an electron off). the mercury doesnt ionize either. it is just a gaseous metal that behaves similar to the noble gasses.

like i said about population inversion... this is what causes the light. ions dont emit light. ions dont exist for long in a gas state anyways.... they only last in an aqueous state because water is a good solvent.

so... sorry about punching holes in your statement, cevinzol, but i just dont think you're right on that one. ionization has no place in populatioin inversion.


If you watch a mercury vapor streetlight turn on you will notice that it takes several minutes for the light to brighten up

just as a last statement, this too is the population inversion in action. it takes a little bit of time to get all the atoms/molecules bouncing around, and this is the warm up phase of the light. once everything is going though, then it is at its full brightness, and we're talking fluctuations of energy levels that happen on the micro/nanosecond timescale (maybe even faster depending on the frequency of the electrical input).

[DaveW]

If you watch a mercury vapor streetlight turn on you will notice that it takes several minutes for the light to brighten up

In Scotland we have sodium lights. Our street lights are orange. When we say that to people, they look at us like we're nuts, but it's not so strange.

-Dave

[Omega]

In Scotland we have sodium lights. Our street lights are orange. When we say that to people, they look at us like we're nuts, but it's not so strange.

-Dave


Heh. Interesting.


Anyways, I have no idea why the "Cold" is there, but the "Cathode" is because a CCFL is essentially a Cathode Ray Tube. The gas inside has electricity run through it, and the gas particles discharge energy in the form of light.

That's about all I know, however.

[Luke122]

My guess is the low voltage required to operate them.

Oh, and we have orange streetlights here too. (in Alberta)

[Slug Toy]

just something to add here. my statement about cathodes using about 4000 volts was wrong. i double checked with my brother the other day, and it turns out i was an order of magnitude too high.... they run on about 400 to 450 volts.

[simon275]

They are cold because they dont have a heater in them they use magnetic fields for the acceleration They dont need heaters also because of the gas they have in them cant remember which though. I now they are over to the far right of the perioidc table. They can still get hot though.

[Slug Toy]

helium, neon, argon, krypton, maybe nitrogen and carbon dioxide... and mercury.

[Guttenaffe]

My guess is the low voltage required to operate them.

Oh, and we have orange streetlights here too. (in Alberta)

Ummm... CCFL's run ~ 600 V @ ~0.1 µA


Also, here in most of Ohio there are orange streetlights as well and they anoy the piss out of me. I hate how they distorts the colors of eveything you look at. I guess they are better because orange is close to the red spectrum and doesn't hinder your night vision as bad a something near the blue spectrum, example Halogen headlights...

[NamesAreUseless]

do cold cathodes have some sort of gas in them cuz I thought if there is a gas in there it will get hot

[progbuddy]

In Scotland we have sodium lights. Our street lights are orange. When we say that to people, they look at us like we're nuts, but it's not so strange.

-Dave

lol me too!
but I live in North Carolina :( .
Our sodium lights do take about 10 seconds to warm up, but thats because ours are pumping some amps.

[DaveW]

10 seconds? I think ours take like 10 minutes. They start of red and slowly change to orange.

They're all getting replaced now with low-pollution lights.

-Dave

[Airbozo]

Orange streetlights here in California, and has been since they hit the market. But then again there are lots of observatorys too. Hell where I live there is 1 non working streetlight in my entire hood and everytime they {used} to fix it, it would get shot out within a week.

But no I did not know the answer to the question.


EDIT: So this is too funny! On my way home last night, I noticed that someone (power company) had been working in our area and thought nothing of it. As I left this morning, I noticed that our one and only streetlight had been fixed again! (after about 9 months of not working). I would bet that it is out gain by tuesday...

[Cannibal23]

after posting i discoverd that this was going to be a redundant post, so i have edited it and removed the content. sorry :-(