Introduction: LED Lightbulb

This was just a lark that had been itching in the back of my head for a while. It's a mains powered LED lightbulb.



Step 1: Supplies

There's not too many things you need for this project.
An incandescent light bulb.
A .47 microfarad 200V capacitor.
1/4 watt 1kilo ohm resistor
a pair of leds
and miscellaneous things.


Step 2: Assembly

You need to start by cleaning out the lightbulb, there are numerous instructables with this step and I will forgo it here.

The circuit consists of two LED's wired in opposition, I ground down the LED's just short of the die and glued them together to make a single double LED. Twist the legs of the LED's together, on one side solder the capacitor, the other the resistor. Simple.


Step 3: Test

Here I'm holding the circuit with a clothespin and sticking it into an outlet, this is of course, the recommended test procedure. ;-)


Step 4: The Bulb

Stick the circuit into the bulb and use some hot glue to hold it in place, be sure to have some cold water, you will burn you fingers. Try to center the LED in the bulb. Once you have the circuit in place, bend one of the leads over the base and secure it with aluminum tape. The second lead is twisted around a brass screw inserted into the hot glue. Check for shorts and you should be good to go.


Step 5: The How What and Why

First to address an oversight, you need a non polarized capacitor for this project, muy importante.

Now, how does this work? We all know that to run an LED off a higher than rated voltage source we muct limit the current with a resistor. Indeed in this case we could limit the current with a resistor of value approx. 6.8K ohms, however that resistor would need to dissipate several watts!!! Not a good thing.

Since we are using an AC source we can take advantage of a property of a capacitor subjected to AC called Reactance. We can equate reactance to resistance. Calculating the reactance is a simple formula

R=1/(2*Pi*Freq*C) Solving this for C will give us the size capacitor we need to limit the current to the LED.

So why do we have a resistor at all? When the power is switched on there is an in rush of current and the 1K ohm resistor is there to limit that in rush current.

Finally, Why two LED's? Well an LED is a diode and since we are dealing with AC here we need to wire two led's in opposition so that the waveform can complete it's cycle. Essentially each LED is flickering at 60HZ but in opposite phase.

Comments

author
KG4ZUZ (author)2010-07-23

You DO NOT have to use a .47 uF mylar capacitor nor do you have to use a 1k ohm resistor, I have built 5 of these lights using a capacitor value ranging from .1uF to .68 uF all at 250 volts or more, I also have used a .uF capacitor with a 2.2k resistor and they all work great. You can use almost any value cap and resistor combination as long as the caps are at least 250 volts.You MUST use a MYLAR type of cap though

author
Aabhishek Sharma (author)KG4ZUZ2017-07-28

You mean ceramic capacitor?

author
ajones40 (author)2012-07-20

If I live in the US, should the capacitor be 110v? Standard wall outlets are 110v here.

author
andr3w99 (author)2012-01-03

I have a question... since i am young, i order from a VERY cheap website... they are the same quality items & i would like for you to help me...
i order from www.TaydaElectronics.com this website is EXTREMELY cheap, but sometimes it is hard to find what you are looking for. Can u help me find the 47 microfarad 200V Capacitor & the 1/4 watt 1kilo ohm Resistor... i dont want to order something, have it turn out its not the right type[s] and have it burn or shock me... thanks

author
boyrock375 (author)2011-11-07

by the way be careful cleaning out the bulb.....when breaking the glass base inside there is an inert gas in there so be sure your carefully and i suggest doing the initial breakage outside

author
.Unknown. (author)2011-08-08

How much current do you think this thing draws, roughly?

author
qwerty156 (author)2011-06-27

Hey!

I pulled out a capcitor from one of those cheap chinese flashlights that charge from ac
It looks a bit like this
http://www.surplus-electronics-sales.com/Zencart/images/products/120-1002%20p1%20radial%20mylar%20cap.gif

Do you think i should give it a try?


I live ina 230v area

author
omnibot (author)qwerty1562011-06-28

Whoa! If you're not sure you shouldn't mess with high voltage! That stuff WILL hurt you. Go through the calculations and read up on the capacitor and safety. Then try it but NEVER mess with mains voltage if you feel uncertain about anything.

author
qwerty156 (author)omnibot2011-06-28

i saw your post just after i tried it lol!

Anyway, the resistor burn out but the leds are fine.

Protip - DO NOT TOUCH THE CAP! Nasty suprise!

author
Daniel Deacon (author)qwerty1562011-06-28

electric shock?

author
Sowee (author)Daniel Deacon2011-06-28

Probably it was damn hot and he burned his fingers.

author
qwerty156 (author)Sowee2011-06-28

nope, it was a shock. scared the crap out of me!

author
wd0013 (author)2011-02-04

To:Tool Using Animal

Awesome post. I especially like the usage of a filter cap in lieu of a (very unnecessary) bridged rectifier. I like bridged rectifiers in larger arrays, but simplicity is always more elegant. Keep 'em coming!

To: Everyone else

As an engineer that does waaaaaaay more dangerous experiments than this, let me tell you all that:

A: There's not enough current draw from that small apparatus to do anything really harmful to the cloths pin. During a malfunction, the cloths pin could get charred, but there would be absolutely NO fire.

B. At the end that is being held (the side with the LED - this side of the resistor and cap), there is only a miniscule amount of power. It takes high voltage to create any kind of arcing across the cloths pin (much less to the fingers pictured here). I'm talking 500+ volts. Voltage levels of 120 - 240 (depending on which country you're from) simply will not arc in such a fashion. Honestly, though you would feel it, there is (most likely) so little power (on the LED side) that you could comfortably touch the leads for a couple of seconds, as long as it was only one hand touching. Of course body chemistry, grounding, humidity, your own level of intelligence , and many other factors means that mileage will vary here. DON'T BE STUPID - MY RESPONSE IS SHOWING THEORY NOT PRACTICE!

The reality is that "real world" electronics testing in the A/C world is typically (at least) this dangerous. Common sense, knowledge, and study are your best friends in the lab (at home or work), so read a book folks!


ONLY THOSE THAT THINK FOR THEMSELVES SHOULD EVEN READ THIS RESPONSE - SHEEPLE GO ELSEWHERE!

author
dany_mid (author)2009-09-06

hi I live in Europe and here my socket electricity has 220V at 92 mA 50 hz please could you tell me what capacitor should i use?

author
Adam Manick (author)dany_mid2010-11-02

Your socket does not put exactly 92 mA. You have to measure it with a load. I think you can use 2 of these capacitors.

author
Adam Manick (author)2010-11-02

A variable capacitor can give you adjustable voltage

author
jules15 (author)2010-10-31

How did you come up with the .47uf cap.. i want to know how to make other voltages like 6,9,12.. Is there a formula?

author
manuhui (author)2009-05-30

Hi, if i want to put more than 2 LED, lets say 8 or 10, I put them in pairs, each pair opposite and with their resistor, in parallel or in series ? is that viable ?

author
megapix (author)manuhui2010-08-27

You would put the pairs in series, and you would still only need one resistor and capacitor for the string. There are a couple of instructibles which do exactly that.

author
noingwhat (author)manuhui2010-07-14

I have the same question, I have an idea for a simple 9 LED array that should make it so that it will work almost as well as a traditional bulb. I just don't exactly know the circuitry for it, and this ible was a good place to start. I still need to know if I should put them in series or parallel though.

author
noingwhat (author)2010-07-16

Is it really necessary to wire two LEDs in opposition? Is the flicker noticable if you didn't?

author
megapix (author)noingwhat2010-08-27

Yes, its necessary, but not because of flicker. LED's have a "reverse breakdown voltage" of only about 5 volts, so a single LED would break down as soon as the line voltage reversed direction. Although the capacitor and resistor might prevent instantaneous destruction, the LED lifetime would likely be reduced. By putting a second LED across the first LED, with opposite polarity, the two LED's protect each other from high reverse voltage, and double the light output, and reduce flicker. What a deal!

author

Dunno, try it and let us know.

author
noingwhat (author)2010-08-15

Ah yes, I forgot about that. Thanks!

author
noingwhat (author)2010-07-14

The wooden clothespin wouldn't conduct any electricity, but there is still the chance of, as he said, fire, or also a spark either from the LED to you, or from the LED to the clothespin spring to you.

author
cicusninja (author)2010-07-08

Is this circuit for 250VAC or 125VAC ? what do I have to use for 250VAC?

author
w0rm5 (author)2010-06-15

Despite of what my freind below says, I built it with a 0.47 capacitor, 1KOhm resistor, conected, lit it up ok, oh really good.......... NOT, after about 1 hour the resistor burned out, so in 127V, it overheats.

author
w0rm5 (author)2010-06-14

Hi, nice one, but what about the capacitor plarity, how do I hook it, negative side to led or the oether way? Thanks

author
Tool Using Animal (author)w0rm52010-06-14

You need a non polarized capacitor.

author
spyler03 (author)2009-05-23

where can i buy the .47 microfarad 200V capacitor?

author
kill-a-watt (author)spyler032010-06-13

search for orange drop capacitor

These are typically 600V, which is over spec, but OK (under spec would not be OK).

You could also take apart old power supplies, if you know what to look for and can do it safely.

author

Radioshack carries both capacitors and resistors. They also carry LEDs for around $2.49 for an ultra bright LED.

author
jules15 (author)2010-06-10

Thank you very much for posting this project. I just finished it and it works great.. Hope to save money : )

author
Darksun010 (author)2010-04-28

Went to Radio Shack and they didn't have a .47 microfarad cap 200 volts, but they had a .047 microfarad cap 630 volts.  Will that work???  It cost a $1.59.

author
taikombuter (author)2010-03-16

I'm a new member ! So, i need you explain more to connect 2 led together.
You can post 1 picture of wiring diagram. Thanks !

author
alzrc_13j (author)2009-09-03

ei what if i use a polarized capacitor???would it make some difference???i cant buy a non polarized capacitor in our place hahahahaha....

author

At best it wouldn't work, at worst, BOOM!

author
tjmortenson (author)2009-12-27

Are they regular 3 volt or 120 volt leds?
 

author

regular 3 volt.

author
crono6894 (author)2009-10-22

the reason he used the clothespin is because it doesn't conduct AS much electricity, but i would wear thick rubber gloves just in case, but that's just me P:

author
tjmortenson (author)2009-10-12

 So are these LEDs regular 3 volt ones or are they 120 volt ?
thanks

author
ensoarts (author)2009-09-28

Wired in opposition? ie positive to postive ? please clarify this point for the clueless. thanks :)

author

Negative to positive, positive to negative.

author
pandyaketan (author)2008-11-18

Simply Brilliant ! The idea of 2 leds in opposite is just too good (i am a novice on the subject, so pl excuse my over enthusiasm...)

would appreciate comments on the safety aspect of it since i plan to make one without the outer glass and using a "male" socket pin to plug it directly in the mains...

reg
ketan

author
H3xx (author)pandyaketan2009-08-05

Haven't made any yet myself, how ever I do know that leds get hot fairly quick when subjected to this much power, as do resistors and capacitors. This design is for using existing lighting fixtures, but it sounds like you are planning at stopping at the test phase when he used the clothespin. It should work and it would be a nice little night light, but I would engineer some sort of shield device, just in case of children or pets or upholstery. I hope this answers your question.

author
H3xx (author)pandyaketan2009-08-11

Well sorry about my timing, I have a habit answering posts without looking at dates. I like your idea though, using a power plug. great job!

author
H3xx (author)2009-08-05

Perfectly logical. And its safe because he's using a flammable, wooden clothespin! :)

author
H3xx (author)2009-08-05

Just a quick side comment, I can understand not wanting to "recreate the wheel" for cleaning out the bulb but a quick link to one of these other instructables would be more convenient for the reader. Other than that, this looks very interesting. I'm definitely trying this. I might replace every bulb in the house. ;)

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Bio: Working my dream job in the Telecom industry, so chances are, i'll never have time to respond to comments or messages, nothing personal.
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