Talk:Cold cathode

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Arc or glow discharge?[edit]

Is a neon lamp really an example of arc discharge? I thought it was glow discharge. A neon sign, on the other hand...

Atlant 18:02, 20 Dec 2004 (UTC)

In German wie distinguish between (Neon-)Glimm-lampe (= neon-(glow-)lamp, a small bulb about 2 mm distance between electrodes, starts to glow at 70 volts as in the screwdriver style voltage tester) and the Neon-Röhre (=neon tube, 2 cm inner diameter and 5 to 300 cm length with 4500 volts to ignite teh arc, and to be coloured by different gas fillings, fluorescent pigments, glass colours) 91.141.97.179 (talk) 08:17, 25 July 2009 (UTC) johannes muhr, graz (A)[reply]

Patents?[edit]

An anonymous editor has added examples of CC patents. Is there any evidence that these particlular ones are practical or have been the basis of any commercial development? Simply browsing patent files is not likely to be very fruitful in this regard. --Blainster 12:16, 14 July 2005 (UTC)[reply]

Well, I'm tempted to give any patent by Philo Farnsworth the "Okay" based just upon his name and fame, and looking at the first patent, it seems reasonably relevant. I'm not sure it goes to "the heart of the matter", but it's not bad or spam or anything like that.

Atlant 15:56, 17 July 2005 (UTC)[reply]

Common usage?[edit]

Right now, if one searches for "cold cathode" in Google, one gets a whole bunch of ads for the PC case mods using "cold cathodes", and mostly after those, comes more generic items. I'd love to see a "Common Usage" section, with at least one question answered: what sort of power supplies are really required? The case mods are all being sold with inverters, which convert from PC power supply input (12VDC, approx. 4W per tube) to (I think, based on some blogosphere statements only) ~300 VAC at some unknown Hz and low current. If this is true, I think it should theoretically be possible to build an AC-to-AC power supply cheaper than those inverters, losing less power to heat in power conversion, and very useful to implement those wonderfully inexpensive cathodes for room and desk lighting and more. Anyone have a clue where to look for the skinny?

Wikipedia isn't the place for manuals or how-to documents, sorry. See Wikipedia:What_Wikipedia_is_not#Wikipedia_is_not_a_manual.2C_guidebook.2C_textbook.2C_or_scientific_journal for some suggestions (and maybe someone can beautify this link, as I don't have the patience to figure out whether it can be, bleah). 72.48.98.26 (talk) 09:36, 17 September 2009 (UTC)[reply]

Regarding your question "what sort of power supplies are required" I added an external link to Everbrite. This is one of several companies who make neon lamp supplies. Hope this helps. WWriter (talk) 19:49, 28 March 2011 (UTC)[reply]

Definition of "Cathode Ray"[edit]

In section 2 the following definition is given:

"Cathode rays - The positive ions created when some electrons are removed from the molecules of a gas at low pressure."

I thought that "cathode ray" was the name originally given to what we now consider to be a stream of electrons being attracted from the cathode towards a more positive anode.

CacheHue 04:22, 9 June 2006 (UTC)[reply]

I'm on your side of the definition, but we should remove that archaic reference entirely.

Atlant 12:10, 9 June 2006 (UTC)[reply]

Weird...[edit]

Whats with the weird comment at the end of the article?

Quote:

Remember kids to put on a condom before putting in your cathodes. —Preceding unsigned comment added by 203.202.21.141 (talk) 03:33, 12 March 2009 (UTC)[reply]

Electron emission[edit]

That chapter is misleading. To my knowledge, field emission is irrelevant for usual glow discharges (it is secondary emission mainly due to ion impact, with some contribution of photoeffect) and field emission cathodes are not subsumed under cold cathodes. – Rainald62 (talk) 11:42, 26 September 2010 (UTC)[reply]

Fixed it earlier this month. -- Rainald62 (talk) 13:31, 16 April 2011 (UTC)[reply]

This article is now completely misleading. A Cold cathode is simply an electrode which emits electrons due to electric field strength, rather than by thermionic emission. The article used to be correct in this respect, but it has been modified by people who don't understand the difference between Thermionic Emission and Cold Cathode operation. 81.187.1.83 (talk) 18:31, 6 September 2014 (UTC)[reply]

I think the distinction between cold cathode and hot cathode is one of construction rather than emission mechanism. A cold cathode may work by secondary emission (a neon lamp), field emission (a mercury lamp), or thermionic emission (an arc). Glrx (talk) 15:41, 9 September 2014 (UTC)[reply]

Cold cathode is simply a cathode operating below its thermionic emission temperature. It is not defined by its construction, but how it liberates electrons (although of course, cathodes are generally designed for optimum operation in one or other mode depending on use case). Some cathodes operate in cold cathode mode and thermionic emission mode at different times (e.g. there are many lamps where cathodes operate in cold cathode mode initially at lamp striking, but transition to thermionic emission mode quite quickly). Most mercury lamps operate in thermionic emission mode (after first few seconds of cold cathode mode in some cases). They can be designed for permanent cold cathode operation, but the much higher cathode fall voltage results in wasted power (and excess heat to be dissipated) around the cathode which is not conducive to efficient operation. 81.187.1.83 (talk) 22:43, 12 September 2014 (UTC)[reply]

No, a cold cathode is one that does not have a heater. Compare hot cathode that says "In a hot cathode, the cathode surface is induced to emit electrons by heating it with a filament, a thin wire of refractory metal like tungsten with current flowing through it.^[1]^[2] The increased thermal motion of the metal atoms knocks electrons out of the surface; this process is called thermionic emission.^[1]".

See also Whitaker page 2512 stating, "(3 – cold-cathode) An electron tube whose cathode emits electrons without the need of a heating filament."

The hot/code cathode distinction is not used to identify the emission mode; that's done with terms such as field emission, photo emission, secondary emission, and thermionic emission.

Mercury lamps are not normally believed to operate in thermionic emission mode; the mercury evaporates at too low a temperature for efficient thermionic emission.

Glrx (talk) 16:33, 15 September 2014 (UTC)[reply]

Yes. And in operation, the cathode might become pretty warm. There is the additional distinction between space charge limited and temperature limited thermionic emission. There should be an article on that. Gah4 (talk) 22:53, 9 September 2016 (UTC)[reply]

References

^ ^a ^b Avadhanulu, M.N.; P.G. Kshirsagar (1992). A Textbook Of Engineering Physics For B.E., B.Sc. S. Chand. pp. 345–348. ISBN 8121908175.
^ Ferris, Clifford "Electron tube fundamentals" in Whitaker, Jerry C. (2013). The Electronics Handbook, 2nd Ed. CRC Press. pp. 354–356. ISBN 1420036661.

This article needs some work[edit]

The wording in the "details" section is highly technical. I have a degree in Computer Science with some experience in electrical engineering and am generally well-rounded technically. Even so, I'm having a hard time figuring out what this section is talking about and why it's important. I think this should be reworded. If you look at one of the pages on one of the reference sites, you can see that it's much clearer and easier to understand: http://www.solelighting.com/node/8

Also, it looks like one of the references is just some company's product page, with no real information on it: http://www.egl-lighting.com/products.html I find that highly suspect and think it should be removed. 209.134.115.80 (talk) 00:31, 24 May 2011 (UTC)[reply]

2015 - still needs work. Perhaps should be renamed to cold cathode device with 'cold cathode' being just a disambiguation. - Much better if all CCFL content moved to a CCFL article ? - Rod57 (talk) 19:05, 28 September 2015 (UTC)[reply]

Clarify the claim that "too low" temperature shortens the lifespan[edit]

How low is too low when dimming the backlight? For example, if I set the brightness of my LCD monitor to 25%, will that increase or decrease the lifetime of its CCFL backlight? SEppley (talk) 17:54, 7 October 2011 (UTC)[reply]

External links modified[edit]

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cold-cathode fluorescent lamp needs its own article[edit]

then we can more clearly discuss eg their characteristics (eg starting/striking, luminous efficiency) and voltage/current requirements. - Rod57 (talk) 18:49, 28 September 2015 (UTC)[reply]

Note 1.[edit]

A negatively charged electrode emits electrons or is the positively charged terminal A negative electrode emits electrons into the device, into the vacuum in a vacuum tube. It is, then, the positive electrode in a rectifier. That is, in a power supply the cathode connects to the positive terminal of the output (where electrons come back in). The terminology is even more confusing in batteries and electrolysis. Gah4 (talk) 22:47, 9 September 2016 (UTC)[reply]

[Avadhanulu-1] Avadhanulu, M.N.; P.G. Kshirsagar (1992). A Textbook Of Engineering Physics For B.E., B.Sc. S. Chand. pp. 345–348. ISBN 8121908175.

[Whitaker-2] Ferris, Clifford "Electron tube fundamentals" in Whitaker, Jerry C. (2013). The Electronics Handbook, 2nd Ed. CRC Press. pp. 354–356. ISBN 1420036661.

[1]

[2]