Introduction: Take Apart a Compact Fluorescent Bulb

Picture of Take Apart a Compact Fluorescent Bulb

Compact Fluorescent Light Bulbs (CFLs) are increasingly popular as a way to save some energy. Eventually, they do burn out. Some seem to burn out annoyingly quickly :-( Even if not burnt out, CFL bulbs have become very cheap, especially if you live in an area where they get subsidized by your local electrical utility.

Are there any hobbyist usable electronics parts inside a CFL? How do they work, anyway? And when they burn out, why have they burnt out?

Let's take some apart and see!

(This Photo by PiccoloNamek from Wikipedia. Hopefully this is sufficient to meet the requirements of the license; I didn't have my lawyer review the Gnu Free Documentation License)

Step 1: Take It Apart 1: Cut a Pry-slot

Picture of Take It Apart 1: Cut a Pry-slot

Most of the CFLs I've seen have a seam where they can be pried apart without too much difficulty. Sometimes the seam is glued or "welded" together, other times it's just where two pieces have been "press fit" together.

Unfortunately, even if only press-fit, the two pieces are usually too securely attached to just pry them apart with your hands, if only because one of the halves has only the glass tube to get a grip on. Sometimes the joining seam is loose and/or large enough to fit in a flat-blade screwdriver, but it is easiest (assuming you don't want to re-use the bulb casing) to cut a shallow slot at the seam with a hacksaw. Just hold the housing securely (in a small vise as pictured, or not), and saw a slot just barely through the casing - about 4mm.

CautionTry REALLY hard not to break the glass fluorescent tube. Aside from sharp edges, fluorescent lights contain phosphors of unknown and possibly dangerous composition, and a small amount of mercury that you'd rather not have released in your home or workshop.

Step 2: Take It Apart 2: Pry It Apart!

Picture of Take It Apart 2: Pry It Apart!

Now that you have a slot, you should be able to insert a flat-blade screwdriver. With a bit of a twist, the rest of the seam will separate (even if glued or welded.) (Hold on glass tube, or it may fall loose and hit something and break.)

(the dangerous (?) mercury is contained withing the glass tube portion, which is sealed entirely separately from the electronics section. As long as you don't break the glass, the mercury stays nicely sealed away...)

Step 3: So What Have We Got?

Picture of So What Have We Got?

I THINK the three CFL "Ballasts" shown here are from a 60W-equivalent IKEA quad-tube lamp, an anonymous 75W-equiv spiral lamp, and a 100W-equiv spiral lamp. The circuits seem to be relatively similar (see next pages), and they have similar components. Other CFLs may have different internals; Vendors are making IC-based CFL Ballast circuits with assorted improved qualities. These three seem to have pretty "dumb" circuits.

(moderately) High Voltage diodes
(moderately) High voltage capacitors - some of these have nice long leads so they can be clipped off without even needing to unsolder them.
Big Inductor - on the order of 2.5 milli-Henries for a 20W lamp.
Smaller Inductor - exact value unknown.
Toroidal Transformer (useful for Joule Thief!)
High Voltage Transistors or Mosfets
Assorted resistors.
High-voltage, High-temp "spaghetti" - this is usually silicone coated fiberglass; useful stuff in certain applications, and hard to find and expensive if you have to buy it.
The Fluorescent Tube itself - if this is still good, you can do things like replace the ballast with a DC inverter and have a battery-powered CFL.

Step 4: What Does All That DO - How Does a Fluorescent Light Work, Anyway?

Picture of What Does All That DO - How Does a Fluorescent Light Work, Anyway?

A fluorescent light is a gas discharge tube. It works a little like a strobe tube, and a little like an LED. Once it's running, it will happily allow very large electrical currents to flow through some ionized gas. To prevent it conducting so much power that it burns out or blows fuses, you have to limit the current with some sort of external circuit (this is the part that is similar to LEDs.) This is the main purpose of the fluorescent ballast. (The other function of the ballast is to get to that "once it's running" state. This can involve filaments, high(er) voltage pulses, and stuff like that.)

The picture shows a simplified fluorescent tube and ballast. You'll notice that the ballast is an inductor. This is because an inductor can act as a current limiter 'for AC current without actually using up any power the way a resistor (as used for LEDs) would. A neat trick. The current through the inductor (and thus the lamp, since it's a series circuit) is proportional to the AC frequency, and the inductance of the inductor. If you've ever seen the magnetic-only ballast from a standard fluorescent light, you'll have an idea how large an inductor is required at the 60Hz AC that comes out of the wall.

Step 5: How Is a Compact Fluoresent Different?

Picture of How Is a Compact Fluoresent Different?

So what's different about a Compact fluorescent?

A CFL tube is pretty much the same as a straight fluorescent; it's just folded up.

To make the ballast smaller, we have to shrink the inductor somehow. Since the current is proportional to the inductance AND the frequency, we can make the inductor smaller just by increasing the frequency! Basically, the electronics in a CFL (or in an "electronic ballast" for conventional fluorescents) contains a circuit that will make HIGHER FREQUENCY AC from the normal 60Hz input.

Typically, the AC input is rectified and filtered to High Voltage DC (HV diodes, electrolytic caps), and then some sort of oscillator (other caps, toroid, small inductor) is used to drive some HV transistors to produce a final output that is still about the same voltage, but at a much higher frequency than the original. This way, the final current-limiting inductor ("big inductor") can be much smaller.

Step 6: What Breaks?

Picture of What Breaks?

Having looked at the guts quite a few dead CFL bulbs, I feel somewhat qualified to point out a few of the reasons that they go bad.

First, of course, the tube itself can go bad, having leaked too much vacuum, or evaporated too much metal internally, they just stop working. When manufacturers quote you extreme lifetimes for CFL bulbs, this is the failure mode that they have in mind.

Unfortunately, a large number of CFLs seem to go bad in the ballast electronics. I've seen them smoke, emit bad odors, and even spark (scary, given the probable flammability of lamp shades.) I've taken them apart and seen obviously burnt components. I'd like to blame this on "cheap imports", but I've had a fair number of brand name CFLs with similar problems. Even some electronic ballasts in circleline fluorescent fixtures. Sigh. (It does seem to be getting better.)

Unfortunately, just because a component on the circuit board is burnt, doesn't mean that that's the component that went bad initially.

The major suspect seems to be the electrolytic capacitors that filter the HV DC. I've seen these with bulging and even burst casings. If you read capacitor spec sheets, you'll discover that such capacitors have a finite lifetime to start with, and that lifetime goes down relatively dramatically as operating temperature goes up. Inside a poorly ventilated casing with 20W of power being dissipated nearby makes for some pretty high temperatures. There ARE high-temp capacitors, but I've never seen one inside a CFL :-( Once the cap goes, the HV oscillator is getting pulsing current instead of DC, which I suspect it doesn't like, and it's not surprising that other things go wrong too.
Some, but not all, CFLs contain a fuse...

The inductors are pretty hardy things; they're probably good unless they show obvious signs of being burnt. The non-electrolytic caps are probably the same, and you can easily test them for shorts using a multimeter. I've never tested any of the transistors...

Step 7: What Can I Do With the Parts?

Picture of What Can I Do With the Parts?

If the tube is still good, you can power it with other types of ballasts or inverters. The picture shows a cheap surplus CCFL inverter mounted inside the spiral of a CFL; the bulb now operates on 5V (and runs about 3W...)

If the inverter as a whole is still good, you may be able to use it to power other types of fluorescent bulb. Search the internet for more detailed instructions.

The capacitors, resistors, and diodes may have general purpose applications, if they're good.

To me, the valuable parts are the inductors; it can be difficult to find inductors in typical hobbyist marketplaces, especially in the sort of high-current versions found in CFLs. The toroid can easily be stripped of its original windings and re-wound for other purposes, such as the classic Joule Thief single-cell LED driver. The small inductor looks like it would fit in many "low tech" switching power supply applications, like The Roman Black Switching regulator or this other white LED driver. The large inductor I'm not sure; in the worst case it also provides a compact core that could be re-wound for special purpose applications.

If you don't use the tube, try to dispose of it at a recycling center that accepts fluorescent lights. They may not be too happy to get ... pieces, but they shouldn't mind TOO much as long as the glass is intact.


Unit042 (author)2017-10-30

Westfw, I know it's a bit late to say something (I just ran across this instructible), but there is a bit of a typo under "Section 6: What Breaks?" where it says this:

Unfortunately, a large number of CFLs seem to go bad in the ballast electronics. I've seen them smoke, emit bad odors, and even spark (scary, given the probably flammability of lamp shades.)

I think the "probably" should be "probable"? Or did you mean "probably flammable lamp shades"?

westfw (author)Unit0422017-11-01

Fixed, even if it is a bit late.

fridelain (author)2016-06-20

The fuse is often shrink-wrapped in one of the wires going to the ballast from the plug.

laci37 (author)2008-11-08

Mercury is very toxic, but its not so dangerous in small amounts like this if there is no strong airflow it stays near the ground.

junits15 (author)laci372008-11-23

u do realize that the amount of murcury in one of these is not nearly enough to kill you, it wont even make u feel sick

Peeet (author)junits152009-08-27

Not the point--heavy metal contamination is cumulative. It accumulates in the body. If you eat shark too many times a week it can be hazardous for the same reason--them being near the top of the food chain we get the end results of their build-up. There are a lot of hazardous inputs that won't make you feel sick immediately.

shomas (author)Peeet2015-05-06

Your body takes in some and eliminates some so it is not cumulative. If it were cumulative, you could have only so much shark over your entire lifetime versus how much shark you can safely eat in a week. For health concerns, it is about how much you take in and how fast you eliminate it that results in either relatively safe or relatively toxic levels in your body.

JungleD (author)shomas2015-12-06

Shomas - Your logic isn't correct: "Your body takes in some and eliminates some so it is not cumulative". The statement contradicts itself. Additionally, it is well established that residual tissue contamination from mercury ingestion is cumulative.There are several different chemical forms of mercury: elemental mercury, inorganic mercury, and methylmercury. The form of mercury associated with dental amalgam is elemental mercury, which releases mercury vapor. The form of mercury found in fish is methylmercury, a type of organic mercury. Mercury vapor is mainly absorbed by the lungs. Methylmercury is mainly absorbed through the digestive tract. The body processes these forms of mercury differently and has different levels of tolerance for mercury vapor and methylmercury.
Mercury vapor, is also absorbed in the sinus cavities and it is here where the behavior of the mercury becomes very strange. It has an affinity for nerve tissue and through the sinuses, attaches itself to nerve endings and steadily travels the nerve to the brain where it then permanently resides and causes damage.

junits15 (author)Peeet2009-08-28

oh i didn't realize it was accumulitive

shomas (author)junits152015-05-06

The accumulative argument is nonfactual and espoused by persons who do not know better. My comment above to Peeet explains why.

tragical217 (author)junits152010-04-24

 are you super sure? I just broke one and I'm freaking out

junits15 (author)tragical2172010-04-24

read below

dawp (author)laci372009-08-28

I think some concern borders on hysteria and lack of common sense. If i should accidentally drop a fever thermometer (there i really dated myself) i don't think i would call the men in the space suits. The XEROX company tried to make a dental imaging machine based on xerographic principals. They found out that the residual mercury in the dentist's carpets "poisoned" the drum. The project was eventually dropped. The same also is said to hold true if somebody breaks a fluorescent tube in a room where a XEROX machine is installed. For us hoomons It is the mercury compounds that are dangerous and that is what accumulates in fish organs, etc. Mercuric chloride is a deadly poison. Years ago our chemistry teachers in high school would pass liquid mercury around the classroom. Now they fire a teacher if he even has a vial of the stuff.

webgiant (author)dawp2013-11-17

Concern about mercury in CFLs does border on hysteria. You could spend months shattering 100,000 CFLs in one spot on your carpet, and once you had finished shattering the 100,000th CFL, you would finally have some cause for worry about mercury poisoning as an adult.

The bigger problem with CFLs, where the hysteria is justified, is pets, children, and the elderly. Mercury affects these groups much more than adults, and children and pets might lick the carpet. So if you have a household with no pets or children, then there's not much to worry about with breaking a CFL.

For those who worry about breaking them anyway, here;s a simple comment: think about the number of times you have ever broken a standard incandescent light bulb. Now divide that number by 10. Since CFLs generally last ten times longer than incandescents, this is the number of times you will break a CFL. Chances are this new number will be less than zero.

bricabracwizard (author)dawp2011-03-01

Yes, I remember being allowed to roll it around on our hands - that's really going back some!! I'm almost 60 - phew!!

rcisneros (author)laci372010-09-01

True. Also it's not that much mercury. There are higher level of mercury it some fish.

richardebueramosii made it! (author)2015-08-07

Dismantling a CFL bulb is like a trip from the electronic hardware. There's a lot of things you could salvage. Thanks for this! I really needed a ferrite toroid for a joulr thief and now I have one, thanks to this guide.

pavelanni made it! (author)2015-02-16

I used a small hand saw before prying the bulb with a screw driver. The rest was easy.

Akshat Ag (author)2015-01-22

This is very usefull for my project

dillonxti (author)2013-10-30

to get mine apart I just whack the seam with a small hammer

james34602 (author)2012-11-01

I use this circuit for my flyback transformer driver

ilovegm (author)2012-07-16

Darn, my buddy gave me a blown out bulb he had, looked like a CFL, he thought it was one too.
When I opened it, all I got was a capacitor wired to a glass glow bulb starter.
Is the starter useful for anything other than lightbulbs?

Inducktion (author)2011-01-09

what can you do with the spaghetti stuff? :0

Itchyzombie (author)Inducktion2012-07-04

You eat it.

Just kidding ;D

Juxe (author)Inducktion2011-05-04

It's a flexible, heat-resistant insulator. It's convenient for big capacitors on small boards, to spread out the components.

ParagonShepard (author)2012-04-13

So could you put a correctly sized capacitor in parallel with the flourescent tube and correct the terrible power factor in these?

no because fluorescent tubes have to have ac current, or the mercury gathers on one side.

ginbot86 (author)2011-11-12

When it comes to harvesting components from CFL bases, be sure to test those transistors. I cracked one open that burnt out in my bedroom and found that the E13003 power transistors were short circuited (reading 0 ohms on a multimeter) between the base and collector, base and emitter, or all three pins.

Higher-wattage bulbs have a (somewhat) greater chance that their transistors would have survived the lamp failing; I have some nice E13007 transistors, and some really nice MOSFETS of which I can't remember the part number right now.

westfw (author)ginbot862011-11-13

yes, you want to be careful harvesting components from bulbs that have actually burnt out in one way or another. The usual failure modes seem to take out several components. But these days the (subsidized) prices of CFLs are low enough that you can think seriously about harvesting brand new CFLs. (I think I've seen 4-packs for less than $5)

laci37 (author)2009-03-25

Mercury is dangerous if you work with it for years, becasue it won't leave the body

xerxesx20 (author)laci372009-05-01

That's right, it's an accumulative poison. The odd amount won't kill you though, the same can be said for radiation -- within reason Rumour has it that in the past it was used as to "cure" many ailments and made your teeth both translucent and green, wish I could remember where I read that.

SKYNET 2.0 (author)xerxesx202009-05-14

People in the Victorian era put Thorium and other radioactive things into toothpaste and cosmetics, they thought that anything as energetic as radiation would have to be good for the body. Mmmmmm...Thorium.

westfw (author)SKYNET 2.02009-05-14

Isn't there still thorium in gas lantern "mantels" ? And don't forget that lovely "uranium glass" and "Fiestaware" pottery containing uranium and produced up through the early 1970s... Of course, the resulting radiation poisoning wiped out the entire American upper middle class during that time period. So sad; they should have known better!

xerxesx20 (author)westfw2009-05-15

Actually uranium glass may still be made, any radioactivity is contained within the glass. It occurs mostly in the green glasswares you see, though many other doping compounds (colourants) are used. As for flame-mantels (I know the ones you mean) i'm reasonably sure they aren't made any with thorium any more, though I could well be wrong, it wouldn't be the first time!

Peeet (author)xerxesx202009-06-18

Radioactivity is definitely NOT contained by glass. The uranium itself is but not the radioactivity. Danger from radioactivity is measured by 3 factors: level of dose, proximity and duration. Some old wrist watches had alarmingly high levels of radioactivity as tested by my scientist brother. This is of concern as proximity is obviously very close and duration of exposure is potentially very long. Old green transparent glass can be radioactive.

xerxesx20 (author)Peeet2009-06-19

Thanks for filling me in there! I suppose the level of (alpha is stopped by pretty much everything that's thicker than paper, so we'll un-complicate things and forget about alpha for now) gamma, or beta recieved depends upon the thickness of said insulating material also how long the person is within range/proximity to the not-very-well entombed source. Interesting that old watches and some glasswares are still radioactive, "uber" long half life I suppose -- difficult to decide how long the half life would be without knowing exactly what radioisotope of uranium it is. I have seen recently a boost in sales of a small transparent quartz/glass/plastic chamber that has a minute amount of tritium gas inside, a so-called "long life" light source without a switch. They are generally traded as keyrings, but are quite costly. £6-8. ($10-15) I was considering buying one, but I have to be careful of my money at the moment, Leadpumper is becoming rather in need of a good service/rebuild. So that's got most of my dosh for the minute!

dawp (author)xerxesx202009-08-27

Hi: Over 10 years ago i got a Mb Microtek watch. It had tritium numerals and hands. It glowed beautifully in the dark; try it in a cave when they turn out all the lights. The guides get mad about that:) In any case, i haven't died of radiation poisoning and it is still glowing in the dark, but not as bright as new. The half life of tritium is around 10 years. The only watch i know of that currently advertises these lights is in Cabela's catalog. I forget the exact name of it. People and regulatory agencies have a fear of the N word and it is generally difficult to get light capsules. In space they are called "Beta Lghts". I think they have also been used in nautical buoys.

Peeet (author)dawp2009-08-27

"i haven't died of radiation poisoning" I'm glad to hear it. There is always a chance that some people will be unaffected by general risks. The fact is that less exposure (which is determined by intensity, proximity & duration) to radiation equals less risk of cell mutation. It is not an irrational fear by regulatory bodies just to make life difficult for us. Some smokers live to ripe old ages, but the vast majority have health effects.

DIY-Guy (author)Peeet2011-10-18

On the original thread:
Kudos to WestFW for a nice -ible on CFL parts.

On the divergent thread:
Tritium is fine IF it's encased safely. Watches with tritium hands have been designed to keep it inside. Regulatory agencies are not always driven by science but often are driven by public outcry and ignorance. Ask a n* physicist who works with those things and they'll tell you the gas lantern mantles and watch hands scare is pretty much just that, scare tactics. Moral- don't grind up any of those things and eat them.

What a great spelunking tool to bring on the tour, a watch face that won't stop glowing no matter how dark it is or how long it has been in the dark!

westfw (author)xerxesx202009-06-19

Don't forget that common potassium is radioactive too.

xerxesx20 (author)westfw2009-06-19

Surely not all forms of it are? There's more than I thought: "There are 24 known isotopes of potassium." -- According to Wikipedia (I'm too tired for "proper" research. lol It's also got a Moh's hardness of just .4 ! Talc(um powder -- it's the same stuff at the end of the day, just smashed and crushed up.) is 1.

laci37 (author)xerxesx202009-06-27

Common potassium(atomic weigth 39) is NOT radioactive. About the hardness of the alkali metals, they are very soft, I have cut sodium with a knife, and it's said that potassium is even softer. But aren't we a little off-topic?

xerxesx20 (author)laci372009-06-27

Thanks for that,and yup, off topic happens to be what makes the world go round. A little disorder is good for the soul, a lot like genuine Chinese chicken noodle soup. "A little nonsense now and then, is cherished by the wisest men..." :-)

SKYNET 2.0 (author)westfw2009-08-27

I remember the infamous fiesta ware. My grandmother kept a set in here bunker-like basement, on day my uncle took a Geiger counter down there to see if we had a radon problem, and the thing crackled away when he set it on the bow of fiesta wear. The offending box was promptly encased in concrete.

SKYNET 2.0 (author)SKYNET 2.02009-08-27

Her* not here

xerxesx20 (author)SKYNET 2.02009-05-15

Yes, indeedy. Watchfaces were often treated with tritium, the "tritium girls" as they were known (I think that's right anyways)(the lasses who applied it to the hands and faces of said watches) didn't live long and sometimes put it onto their hands or teeth as a practical joke. Mercury is still poisoning people today in one of OSRAM's facilities in China -- I read about this recently in the press -- though you can't always believe what you read!

BOOM5601 (author)xerxesx202009-09-05

Tritium is a more fun isotope of hydrogen. Not only does i still go boom, it's also radio-active! And it was radium on the watch faces. They were tought to put the brush in their mouth to straighten it out for more delicate painting. Mmm, radium.

1BigKid (author)xerxesx202009-08-27

I often wondered about the Tritium. The Night Sites on my work gun, a Sig Sauer p220, are manufactured by Trigicon and use Tritium as it's power source. They are encased in metal and what appears to a thick plastic dot (maybe glass) I don't know how long these sights have been in production or their intended shelf life but I was issued this firearm about 5 years ago and they still glow very brightly in low light situations! I suppose it is like everything else though, they sell it and say it is safe but 20 years later they will tell you it causes cancer or something! I know we strayed off topic a bit but it is interesting anyway. A true conversation piece of an Instructable!

rexmo (author)1BigKid2009-08-27

tritium is not nearly as dangerous as radium and has a much shorter half life

rexmo (author)xerxesx202009-08-27

it was not tritium, it was Radium.

About This Instructable




Bio: Middle aged geek username also works at,,,
More by westfw:Visualizing EAGLE Edits with a Gerber ViewerMake a Double CD/DVD Case From a Single Sheet of PaperSingle Sided Really Bare Bones Board Arduino in EAGLE.
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