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What is the Resistor to use for 2 Green LED in series connected to 6V ?

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Bracer

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What is the Resistor to use for 2 Green LED in series connected to 6V ?

Assuming that those green LEDs are your "typical" LEDs.

What about Blue LEDs ? What Resistor to use for 2 Blue LEDs connected in series to a 6 volts ? I suspect no Resistor would be required for 2 Blue LEDs in series to 6 volts could someone confirm that ?

I am currently using 470Ω when I am connecting a typical LED to a 6 volt regardless of color.
 
Colour will make no difference at all; the resistor you need will depend on the power rating (thus current drawn) of the LEDs; hence it's not possible to give you an exact answer without this information; check data sheets from wherever you bought them. Unless you want to be outputting as much light as possible without the chance of blowing them, pretty much anything between 50-400 ohm should be fine. A 470 or 1k pot might be your best option, then you can experiment.
 
What about your "typical" LED ?

That is why I use the word Typical because I have gotten these LEDs through an "assortment" sale and no data was provided, that is why I use the word "Typical".

Assuming that the power source is a 6 volt battery, what is the ohm to use for two green LEDs [Typical] connected in series ?

What is the value for 2 Blue in series ?

What about two Red in series ?

Thanks.

Yes, they are "typical" LEDs, and to use a MADTV reference, I lost my clairvoyance abilities when I was six so no, I can't go back in time and ask the root creator the exact specs for the LEDs....
 
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I believe the attached is what you are getting at with the word typical. However, with the advent of so many new LEDs in so many flavors the old "typical" may not apply as well as it once did. Anyway the attached image gives an overview. I assume you can do the math for the LEDs based on applied voltages? Vsupply - Vled / Ifwd led = series resistance.

For a mountain of generic LEDs it would not hurt (as mentioned) to place a pot in series with the LED(s) and experiment for desired brightness and note the voltage and current.

Ron
 

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What about your "typical" LED ?

That is why I use the word Typical because I have gotten these LEDs through an "assortment" sale and no data was provided, that is why I use the word "Typical".

Assuming that the power source is a 6 volt battery, what is the ohm to use for two green LEDs [Typical] connected in series ?

What is the value for 2 Blue in series ?

What about two Red in series ?

Thanks.

Yes, they are "typical" LEDs, and to use a MADTV reference, I lost my clairvoyance abilities when I was six so no, I can't go back in time and ask the root creator the exact specs for the LEDs....

"Assume", a bad word but has to apply in this case, that each LED has a Vf of 1.2V and that its If is 20mA, two in series that is 2.4Vdc then 6.00Vdc - 2.4Vdc = 3.6Vdc (across the resistor) at 20mA the series resistor is thus 3.6Vdc/0.020A = 180R !
 
I love you Reloadron!!!
That chart you have attached is one of the most important chart I have encountered.

Thank you Graham2107 for doing the Math for me :)
 
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I have some modern very bright green LEDs that are made with the same chip as a blue LED so their forward voltages are the same at about 3.3V. Two in series would be very dim with a 6V power supply.
They are in clear packages.
 
Just make sure that they work at 1.2Vdc first as all the blue LEDs I have work at 1.2V
No.
Nobody makes a blue LED that has a forward voltage of only 1.2V. Their voltage is from 3.0V to 4.6V for an ordinary 5mm one.
Did you know that a white LED (not an RGB LED) is actually a blue LED with a yellow phosphor on top? So its voltage is also from 3.0V to 4.6V.
 
Normally the resistor is calculated based on R = (Vs - VLED) / Iled. We need to apply more Vf for the Blue & White LEDs
 
According to Reloadron's chart, it seems my usage of 470 Ω for typical LEDs running off 6volts are way too high :)
Seriously that chart saved my life :D
 
That chart is no more than a general (very general) reference. Remember the best approach with any large lot of LEDs and no spec sheets is to try a few resistances and note the forward voltage drop across the LED and the forward current through the LED for optimum brilliance. Remember a LED is after all a current device and the little buggers keep evolving. :)

Ron
 
Is one able to use a meter to retrieve the forward voltage and current of the LED ?
I was given the notion that only the manufacturer know.

If it can be measured, how ? What is the procedure to go about doing this :)

Thanks.
 
Is one able to use a meter to retrieve the forward voltage and current of the LED ?
I was given the notion that only the manufacturer know.

If it can be measured, how ? What is the procedure to go about doing this :)

Thanks.

It isn't quite an exacting science but yes you can use a good DMM to read the voltage and current. Place for example a 1 KΩ variable resistor in series with the LED and working from High to Low resistance reduce the resistance till the LED glows nicely with a good brilliance but not super bright. Measure the voltage across the LED. Next place the DMM in series with the LED and the pot and measure the current. Don't change the pot settings from the last measurment. That will give you the current for the given voltage drop across the LED. Like I said, this is not a very exacting science. :)

While a very bright LED is noticible it may have a very short life if we over current it.

Ron
 
Manufacturers don't know the forward voltage of the LEDs they make which is why it is listed as a range of voltages in their datasheet. Which is one of the reasons why you can never power a "3V" LED from a 3V battery without a current-limiting resistor. The "3V" LED might actually be 2.7V and instantly burn out or might be 3.3V and be very dim or produce no light.

Ordinary 5mm diameter LEDs are operated at 20mA to 25mA to be bright. Their max allowed current when they are cooled is 30mA.
The current can be simply calculated with Ohm's Law by measuring the voltage across the current-limiting resistor then dividing the voltage by the value of the resistance.

I test LEDs with a new 9V battery and a 270 ohm series resistor.
1.8V red LEDs have a current of 26.7mA.
2.2V older green LEDs have a current of 25.2mA.
3.3V blue or white LEDs have a current of 21.1mA.
 
No.
Nobody makes a blue LED that has a forward voltage of only 1.2V. Their voltage is from 3.0V to 4.6V for an ordinary 5mm one.
Did you know that a white LED (not an RGB LED) is actually a blue LED with a yellow phosphor on top? So its voltage is also from 3.0V to 4.6V.
But I have white LED that are in clear case, so there cannot possibly be a phosphor coating for those LEDs.
Does that means that those LEDs are thus pure white ? No faking ?
 
Read this link. I suggested, in answer to your question earlier, how to measure the forward voltage drop and current. White LEDs typical Vf is 3.6 volts and figure 20 mA. Read and understand the different ways LEDs get their color.

Ron
 
A white LED is in a clear plastic case. You can see the yellow phosphor inside on top of the blue LED chip.
Look at the datasheet of any white LED and the brightness of the blue and yellow colours are shown.
 
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