Cold Cathodes

[zander1976]

Hey Everybody,

I have cold cathodes in my computer lighting it up. I was just wondering if people ever thought about using them for lighting a room. I big version obviously.

Oddie

[12AX7]

Cold cathodes?

What about the anodes?
I guess I don't understand??   Your monitor is glowing while being disconnected from every/anything?

ax7

[Ungrounded Lightning Rod]

I believe he's referring to cold-cathode fluorescent tubes, like the ones in LCD monitors.

These use a single hunk of metal in each end and an electronic ballast that applies a voltage high enough to strike an arc in the carrier gas, rather than a heater-filament in each end to serve both as an electrode for the arc and to initially evaporate some mercury and/or emit some electrons to bombard the mercury on the side of the tube to get the lamp started.

Each end alternates between being a cathode and an anode.  Don't ask me why the focus on its cathodic function in the nomenclature.

[DamonHD]

Because normally you'd (have to) heat the cathode to get enough electron mobility?

(Note that LCD screens use much less energy when backlit with LEDs then with cold cathodes, so I suspect that efficiency of CCs in not all that great.)

Rgds

Damon

PS. Here's what Wikipedia says:

A cathode is any electrode that emits electrons. When used in electrical and electronic devices (most fluorescent lamps, vacuum tubes, etc.), the cathode is explicitly heated, creating a hot cathode. By taking advantage of thermionic emission, electrons can overcome the work function of the cathode without an electric field  to pull the electrons out. But if sufficient voltage is present, electrons can still be stripped even out of a cathode operating at ambient temperature. Because it is not deliberately heated, such a cathode is referred to as a cold cathode, although several mechanisms may eventually cause the cathode to become quite hot once it is operating. Most cold cathode devices are filled with a gas which can be ionized. A few cold cathode devices contain a vacuum.

[hydrosun]

I saw an alternative energy web site in New Zealand that was selling pricey spiral 12 volt cold cathode fluorescent (CCFL) lights a few years ago. They were claiming higher efficiencies than standard fluorescent lights. I looked around the web and only found the straight tube ccfl at a reasonable price. I bought 10 sets and have used them for the last few years. I made some funky white paper reflectors and glass covers.  They do seem reasonable bright for 8 watts (2 four watt tubes on one ballast)  16 watts lit up a 10 by 8 foot room better than the 30 watt RV 12 volt fluorescent that they replaced.   I have had several ballasts fail early over the wood stove where it gets too hot.  The one in the bathroom and kitchen get used every day and have lasted at least 4 years. So my experience is that he ccfl have some merit if they aren't too expensive.
Chris

[thirteen]

Hydrosun  I am not sure of your voltage being used but maybe for your lights over the wood stove you could look into finding an old computor and take one of the smaller cooling fans and mount it so it blows over the ballast. They do not use very mush energy and you could maybe mount a thermosat to control it.  It might save some time and $$.  Just an an idea to laugh or toss.

[dnix71]

I use 120v cold cathode fluorescents in two porch lights. They're dimmable. Home Depot sells them cheap. Very good efficiency, too.

http://www.google.com/products/catalog?oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&q=5w+cold+cathode&um=1&ie=UTF-8&cid=11984265651621994219&ei=X2xwTLrKOIW8lQe0zfjDDQ&sa=X&oi=product_catalog_result&ct=result&resnum=3&ved=0CCoQ8wIwAg#

Severely overpriced at the link above. They are $6.50 for a two pack at Home Depot. Soft start, take a few minutes to fully light. 2 1/2 times the life of standard fluorescents, too, at 20k hours.

The 12v cold cathode lights can be bought from any auto store. That's what people with too much money put under their cars to make them look fancy at night.
http://www.instructables.com/id/Install-Computer-Cold-Cathode-Lights-Into-Car/   computer cold cathodes installed in a car here.

[zander1976]

Yeah, I have blue cold cathodes in my computer and pink in my wifes..

[Bruce S]

IF you're into recycling you can find the CCFL's in old and new scanners too.
VERY bright and free if the other electronics have already let out magic smoke  .

Bruce S

[independent]

Thought I read it here.. Anyway, confirmed on Wikipedia, half as efficient as good normal fluorescent technology in general.