Talk:Compact fluorescent lamp

Actual cost
Someone please add the actual costs, because comparison to incandescent is not effective. — Preceding unsigned comment added by 67.231.65.195 (talk) 15:04, 7 February 2024 (UTC)


 * Additionally, the article should be updated, since LEDs have risen tremendously in energy efficiency. Even cheap IKEA LEDs are advertised with 1521 lm per 8.2W, equaling 185,5 lm/W. Newest LEDs have broken 200 lm/W. 88.152.11.83 (talk) 14:38, 2 May 2024 (UTC)

Incorrect external reference
Citation 39 does not link anywhere (energystar.custhelp.com). It should be corrected or removed.

End-of-life failure mode
Can someone add something about end-of-life failure mode? I have repeatedly seen irregular flickers starting about 30 minutes before sudden blackout. BMJ-pdx (talk) 11:16, 12 April 2017 (UTC)

Color rendering
The offered 4-page reference no-where makes the assertion that LED lights and fluorescent lamps do not render color well. It even says that lamps with a CRI over 80 will be acceptable for indoor installations. Lamps intended for color-matching duties are not required for general illumination. --Wtshymanski (talk) 15:30, 29 April 2017 (UTC)

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Cold cathode fluorescent tubes
The term 'cold cathode' with respect to these devices (CCFLs) refers only to the fact that the electrodes are not independently heated. It does not mean that the electrodes operate at or anywhere near ambient temperature. The electrodes are heated by the electron bombardment of the discharge in the tube. Once fully warmed up, they operate close to the temperature of the heated electrodes in normal fluorescent tubes and indeed rely on thermionic emission. The big give away is that the light output of the CCFL is low when power is first applied and they slowly get brighter as the electrodes warm up (for these tubes, they get brighter at the ends before the middle). The electrodes certainly do sputter, though the material with which they are coated is designed to resist sputtering as they are forced to discharge while cold.

Luckily I have a CCFL here which is 7mm in diameter and 250mm long. The ends, though not as black as CFL tubes can get after similar use, are a medium grey at one end and a darker grey at the other compared with the rest of the tube (it has seen a lot of use and is around 25 years old). At start up, the tube emits 960 lumens/m2 (not corrected for colour temperature). After approximately 2 minutes the light output has risen to 3200 lumens/m2. The tube ends eventually reached their operating temperature of 165 C after five minutes or so. The centre of the tube is more comfortable 39 C. For the tube ends to get that hot means that the electrodes must be much hotter than that. Standard fluorescent tubes don't usually get that hot but only because they are of a larger diameter so there is more glass to heat.

If you run the tube in a darkened room and avoid looking at it while it is lit and then shut the power off and quickly look at the ends, you can just make out a very dull red glow through the phosphor for a few tens of milliseconds or so before it quickly disappears. It is better observed on a germicidal CCFL lamp which has no phosphor, because on these lamps the red glow of the electrodes is visible while the lamp is operating (but do look at it through a piece of glass!). A red filter makes it much more obvious by filtering out the blue discharge. 86.164.61.30 (talk) 13:34, 26 August 2021 (UTC)
 * This is way false. Preheat and instant start fluorescent heats the electrodes exactly like CCFLs. The only difference between fluorescent and CCFL, is that fluorescent relay on thermionic emission, so if the cathodes are cold, they sputters fast. CCFLs don't relay on thermionic emission, so if the cathodes runs cold nothing happens. זור987 (talk) 13:40, 26 August 2021 (UTC)


 * No it's not false. You clearly do not understand the technology as much as you think that you do. If nothing happens when the electrodes are cold as you claim then the lamps would not light when power is first applied because the electrodes are cold. And they are not cathodes because they act as anodes as well, so they are just electrodes. The term 'cold cathode' is a hangover from tubes that have unheated cathodes but work from DC, such as voltage regulator tubes (and those cathodes get hot as well, but nowhere near as hot as in CCFLs).


 * They do not rely on thermionic emission when first switched on because the electrodes are cold, but as the lamp warms up, the discharge current rises as thermionic emission becomes the predominant form of emission. Why else would the brightness increase with warmup?. The period during warmup causes sputtering, but far less so than with 'hot electrodes' because (a) the oxides used to coat the electrodes are more able to operate this way by design and (b) the current density is much lower, which it must be because the tube voltage drop is much larger. If I could upload photographs, I could show you my lamp with blackened ends. This can only be caused by sputtering.


 * Why do you believe that all CCFLs are 3mm in diameter? My CCFL at 7mm says that you are as wrong on this point as every other point that you make. I also have another CCFL in my junk box that was rescued from a scanner that is 10mm in diameter.


 * Since the section is now completely wrong but more importantly, it is completely unreferenced, it has been deleted. It must not be restored in any form without references. 86.164.61.30 (talk) 17:32, 26 August 2021 (UTC)
 * Cold cathode fluorescent lamps don't rely on thermionic emission. If they are underdriven so that their cathodes run cold, their life will be very long compared to if they would run hot. This is why their electrodes aren't filaments and don't have emissive coating. Regular fluorescent lamps rely on thermionic emission, so when they are underdriven, their cathodes don't heat enough for thermionic emission, resulting in fast sputtering and short life. — Preceding unsigned comment added by זור987 (talk • contribs)
 * The cathodes on CCFLs do not run cold as many people seem to assume. 86.164.. is quite correct when he says that the description “cold cathode” solely refers to the fact that the cathodes have no provision for heating them other than the heating from the discharge. This is what “cold cathode” means by definition. If you run a CCFL for ten minutes or so, then turn it off and pick it up by the ends, you will be left in no doubt whatsoever that the cathodes run very hot indeed. I would not recommend that you try though because the burns may take some time to heal. CCFLs have to be mounted in such a way that this heat does not damage or burn the fixtures.
 * The cathodes are indeed coated (though obviously with different materials as already noted), and the mechanism that heats the cathodes is exactly the same as the heating of the cathodes in a normal fluorescent tube once the discharge is struck. The cathodes in ordinary fluorescent tubes are not intended to be electrically heated while operating and indeed in a magnetic ballast circuit with a thermal, manual or glow starter they are not. Other circuits may maintain a low heater current but not enough to heat the cathodes to operating temperature as the (heater) current rapidly falls as the discharge current rises.
 * CCFLs can be dimmed because their cathode coatings are designed to be operated in this manner though there is a limit to the amount of dimming because the cathodes can become too cold to sustain a stable discharge. Ordinary fluorescent tubes cannot normally be dimmed because the coatings used are not designed for such use. I say “…cannot normally be dimmed…” because they can be dimmed if operated from special dimming ballasts without any compromise to life. 185.69.145.169 (talk) 13:58, 28 August 2021 (UTC)

I have no clue where you all are getting your information, but it certainly isn't from reliable sources. I would suggest forgetting the internet and try looking in books. There is a ton of bunk info out there online, and much of the good information is still only available in books. I'd suggest really good books by reputable publishers, such as Lighting Control: Technology and Applications, Phosphor Handbook, Fluorescent Lighting Manual, Electrotechnology Practice, or Philips Technical Library - Fluorescent Lamps, to name but a few.

First, fluorescent lamps that preheat the cathode filament are called "rapid start" lamps. The purpose is to allow the lamps to strike at a lower voltage and transition from a glow to an arc more quickly, thereby reducing sputter and extending life. Otherwise, nearly all fluorescent lamps operate as an arc, but for those without preheating it takes them much longer to heat the cathodes, the glass, and the liquid mercury to vapor point, and the striking voltage is much higher, so they wear out faster when switched on and off repeatedly.

Now, for an arc to form, it requires thermionic emission of electrons from the cathode. (Note: for AC circuits, the cathode and anode switch sides for every half cycle.) For the typical Philips tungsten electrode (which has become the standard design for virtually all lamps), this means that, in addition to the voltage drop of the gas column, you get a very high cathode fall at the cathode, often in the range of 50 volts or more. When the proper temperature of the cathode is reached, this cathode fall suddenly drops to about 6-10 volts, the flood gates open, and electrons are suddenly free to pour into the gas. The temperature at which the metal must be heated for this to occur is typically between 1600 and 2500 degree F (a blackbody temperature of orange to white hot), or approaching the melting point of steel. The entire cathode doesn't need to be heated to this temperature, as heating only the surface is sufficient, for example, the uncontrolled arc of an arc flash or a flashtube. But it must be heated to the proper temperature or no arc will form.

Fortunately, fluorescent tubes are more controlled than an arc flash, and they take a bit of time to warm up, for internal pressure to increase less violently, and for it to transition to an arc. Until then, they operate as a glow discharge.

Cold cathode lamps were actually the first fluorescent lamps. These operate just like a neon light; they never transition to an arc and operate in the glow regime. The voltage is kept very high, typically anywhere from several hundred to tens of thousands of volts (depending on size and application), and the cathodes are cold in comparison to an arc lamp (typically just a few to several-hundred degrees F). As a glow, the electrons barely have enough energy to overcome the pull from the cathode's electric field, and most just fall back to the cathode. The few that escape are basically spent of all their energy by the time they escape the negative field. It's at this point, in the "Faraday darkspace" that the electrons just kinda slough up, and as they eventually begin accelerating toward the anode, most of them just decide it's easier to go around the positive column, creating an electron sheath around it. Nearly all the current then flows in the dark spaces around the gas rather than through it, and all the light produced by the positive column is due to induction and the accompanying eddy currents. The negative column is almost always proportional in length, but the positive column can extend to whatever length the tube is. The lifespan is exceptionally long, because most metal sputtered from the cathode doesn't have the energy to escape the field, so it falls back and is redeposited right back onto the electrode.

For CCFLs, they operate at a much lower gas pressure, the electrodes are solid metal (no filaments) and nearly the all the mercury is already in vapor form due to the much lower pressure, so they start instantly and run very reliably. The easiest way to spot them is that, because of their high voltage/low current, they run off of transformers rather than ballasts, and the reactance of the transformers alone is enough to limit current. Zaereth (talk) 22:06, 14 September 2021 (UTC)