LED Lightbulb

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

[dany_mid]

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?

[Adam Manick]

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.

[Adam Manick]

A variable capacitor can give you adjustable voltage

[manuhui]

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 ?

[megapix]

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.

[noingwhat]

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.

[w0rm5]

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.

[jules15]

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

[pandyaketan]

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

[H3xx]

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.

[pandyaketan]

Too Late Now !

http://www.instructables.com/id/LED_night_light_lamp_bulb_on_AC_Power_mains/

reg
ketan

[H3xx]

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!

[wkumtrider]

Where do you buy your electronic parts? A .47uf 200V capacitor is hard to find.

[snowtires]

go to mouser.com and you'll find just about everything you need

[Tool Using Animal]

ebay

[Body4Change.com]

So this is a very low wattage light source? (sorry, new to the subject)

[MattieShoes]

LEDs consume about 20 milliamps of power at 3-4 volts, which is around .07 watts of power consumed. The resistor and capacitor probably consume some power too. Consider that those wall warts you've got plugged in that aren't actively being used are eating as much as 15 watts each, 24 hours a day, and this is essentially free light. Dim, but free. :-)

[Tool Using Animal]

Very very low.

[godfreyandthandi]

very very low wattage lol nice try