I wanted a blue LED light bulb for our water dispenser. So I decided to make one.

You need...

3 blue or white LEDs
1 100K 1/2W resistor
1 1N4004 Diode
1 dead (or not) C7 socket light bulb
3 inch of 1/2 " shrink tube

some hot glue
Soldering Iron
Paper tube (paper towel or toilet paper tube)

Step 1: The circuit

The circuit is composed of a 1N4004 diode, a 100K 1/2W resistor and 3 blue LEDs
<p>Doesn't the resistor get really hot having to drop the voltage so much?</p>
<p>Blue LEDs have a forward drop voltage of about 3.3 volts. Since we have 3 in series, plus a 0.7 Volt drop on the diode, we have 10.7 volts drop on all of them. 109.3V remains, to be lost in the resistor.<br><br>The total power in the resistor will be : V&sup2;/R = (109.3)&sup2; / 100000 = 0.119 W. Since the resistor can take 0.5 W, the heat should not be a problem, but nothing stops you from using a bigger resistor if you want.</p>
This may be a dumb question, but I'm an amature when it comes to circuitry. You are talking about running this bulb on 120v AC 15-20A, like out of a standard U.S. wall socket right? I checked on what a C7 bulb is for and it was saying AC and a C7 is one of the big old Christmas lights. Sorry if this is a dumb question but i thought you had to have a bridge rectifier and a couple of caps to make LEDs work with AC after power correction (or b4). Like I said, I'm new to circuitry, so bear with me please.
The voltage is the potential and the amps is the actual flow of electrons. By putting the resistor in you cut down the amps, and because it is a light emiting DIODE, if you put reverse voltage to it (alternating) it will block it (for the most part) and not light up. What you are actually seeing is it flashing at 60 times a second. Otherwise, yes, you would need a rectifier and caps. Sorry for the spelling, my "check spelling" button is having problems.
ok, so if i wanted to brighten them up a bit, i would have to use a cap to smooth out the signal right? what farad value should i use? (for that matter how does one choose a cap value for any application?) i've got 3 super-bright white leds in series and they're not that bright at all. not to mention that they are pretty directional and i end up with 3 circles on the lampshade. i was gonna use some lighting gel diffusers to try and spread the light out, but it still looks dimmer than they should be.
No, you would use a lower resistance. Be careful if you go too low you will burn out your LEDs sooner than they should. The caps would be to filter out AC noise from the line. You could try putting the LEDs in parellel instead of series.
If you put the LEDs in parallel one will tend to draw more current and dim the others. Parallel ensures that they all get the same current. Just lower the resistor if you want more current.
You don't need a rectifier to make them brighter, just more current. In another post I calculated under 2mA driving the LEDs, so there is a lot of room for higher current and thus brightness. They're being pulsed so you can drive them higher than their DC current rating.
Why do you what to use a cap for? I have no caps and the light is not flashing. LED are diodes, BUT they don't have a very high reverse voltage, this is why the diode is there on the AC. The resistor is for limiting the current. Each blue LED drops about 3V. So the rest of the voltage will be at the resistor and diode...The circuit works, it does not heat, and there is no flicker. This is a K.I.S. circuit... There is no reverse current to the LED because of the diode 1N4001 and the current is fairly low and not stressing the LED. This is going to last a long time. Plus it's so compact, I was able to make it fit within the size of the original bulb.
Kind of an old comment, but If you are only using one diode its a half wave rectifier and therefore only flashes at 30 times a second. If you were to use a bridge rectifier, then it would be 60 times a seconds or hertz.
Actually it's 60 flashes a second with the half-wave rectifier; a 60 Hz sine wave has 60 positive peaks and 60 negative peaks per second.
You can double the flashing rate to 120Hz without any rectifier or caps (see my other posts).
It will work on any 120V circuit. I used a C7 (Christmas lights socket) because this is what's used into my fridge water dispenser. Originally, I left the thing running for a week on my desk before I actually made the final assembly. There was no significant heat. The final assembly has been lighting up my water dispenser for a month now. Don't think it's CSA or UL :')
what does the 1 diode do? and how is the led not overvolted??
Oh, and regarding &quot;overvolting&quot;, the resistor prevents that. When the LEDs have sufficient voltage running through them, they'll draw pretty much whatever current you feed them, so the resistor will drop the voltage to their forward voltages. Let's say the LED's forward voltage is 3.3V. Three in a row give 9.9V, plus the ~0.6V drop of the 1N4004 diode, so about 10.5V. The 120V (RMS) AC peaks at 170V, so the resistor will have 155V across it and deliver 155V/100K = ~1.6mA @ 3.3V to each of the LEDs during the peak of the cycle.
The diode presumably has a higher reverse-breakdown voltage than the LEDs, so on the negative half of each cycle, it ensures that there's negligible reverse voltage on the LEDs. But a more elegant solution is to just put the LEDs in parallel in opposite directions (see my other post).
in the darkness, red light is more comfortable to the eyes&nbsp;
Blue is also apparently bad for humans to be around at night because it disrupts the sleep cycle.
Yes, Blue light is harsh on the eyes in the dark. Green would be better than blue, but Red is much better yet. Star Gazers use nothing but red to move around their telescope sites to preserve their night vision.
Well, it's not my circuit, but I&nbsp;can tell you that the 1N4004 is because LEDs typically don't handle the high reverse bias voltage that will be applied to them (60 volts) on the negative half of the AC power.&nbsp; So only the positive part of the AC power will be applied to the LEDs.<br /> Not sure what current the LEDs are rated for,<br />
Wouldn't it make more sense to use an even number of LEDs and wire them reversed in parallel, such that on each half of the cycle one pair of LEDs is running? Then neither is getting reverse voltage above a couple of volts, and no need for an extra diode (the LEDs themselves are diodes). This also raises the flickering frequency to 120 Hz, making it much less noticeable.
<em>&quot;</em><em>Brake a C7 bulb but don't brake it!&quot;</em><br> <br> Why would you need to <em>brake</em> the bulb? How fast is it moving?<br> <em>Braking</em> is how you get your car or bike to stop moving (unless you crash it to stop, too hard on the vehicle... and you).<br> <br> <em><strong>Breaking</strong></em> is what you are doing to the bulb's envelope when you squeeze it in a vise.
Your circuit looks very simple. I wanted to try something like this for a painting a friend of mine did. I have a couple of questions. 1. Why did you include the 1N404 diode in the circuit? 2. Are the leds the 3.2v at 20mA variety?
You must use a bridge rectifier to give full bright to the leds and remove the stroboscopic effect.
I can assure you there it is not flashing at all... I know it should but it's not and it's the perfect brightness. It's much better than the original that use to light up half the kitchen... :-) there's always more than one way to do this... I tried to keep it as small as possible to fit in...
Wouldn't it make more sense to get one of those small Bridge rectifiers from radio shack, but put the resistor before it because they are only rated for about 50v?
If you are REALLY using the circuit on a 120v system, you should be aware that the 1N4001 diode is only rated for 50-volts! Each of the LEDs can only take 5-volts, so all 4 in series are only rated for 65-volts!<br/><br/>You may have been lucky that the 1N4001 you got has a higher tolerance, but others using your plans may not be so lucky.<br/><br/>I suggest you use at least a 1N4003 and/or another 1N4001 to block the reverse AC current!<br/><br/>See <a rel="nofollow" href="http://www.instructables.com/id/Using_AC_with_LEDs_Part_2_and_make_this_handy_/">this</a> for some calculations and ideas.<br/>
Actually you are right and a 1N4004 was used. The reason why I did not use a capacitor in this circuit is the size. The circuit must fit inside the door panel of the water dispenser. Also the reason I used an old bulb socket, was to NOT void the warranty of this new fridge. It would have been easy to make a circuit the is larger then just tap on the existing wire. I did not what to take a chance in case something else on the fridge goes wrong. You know how companies can be with warranties.
aww! no pictures of it in use. Ah well. Good job though, I made a similar thing with an old hand powered flashlight bulb that was broken, though it produced 6v ac, so I didn't worry too much about it, works great i used candle wax for an insulator.
New Picture of it on line now...
I will try to post a picture of the inside of the water dispenser... The blue light is hard to see...

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