Leds question.

[BT1324]

Hi,
i have a few questions about leds. How many volts do you need to light up a led and if i use two, does that mean ill need double the voltage?

 

[raggie33]

it depends on the led

 

[milkyspit]

Raggie's right about the voltage depending on the LED.

If you hook two identical LEDs in series, you'll need double the voltage. If they're hooked in parallel, you'll need double the current.

 

[James S]

If you mean white/blue/green then you'll need between 3 and 4 volts for normal 5/3mm ones. I think the specs say 3.2 or 3.4 volts max, but they do vary by individual. The red/yellow/orange ones run at a lower voltage. 2.something usually.

Otherwise the other info here is correct.

Some folks will also warn you that the forward voltage on different LED's is different enough that if you wire them all in parallel that if one has a low enough voltage it will run away and overheat while the others are OK. I have not had this problem with LED's that I bought in a single batch, but definitely see it between purchases. You can run at a slightly higher voltage and put a separate resister on each one.

If it's possible to get enough voltage to run several in series, this is the way I prefer to do it. They even out quite nicely that way.

 

[eluminator]

There ought to be a primer available here for beginners that want to light their first LED. How to calculate the size of the ballast resistor etc.

It's pretty simple stuff, but a newbie has to learn it somehow. This info may exist somewhere on the internet, but I don't know where.

 

[BT1324]

hey,
thx for the info but how come i see flashlights with like 20 leds and only use two D batteries?

 

[shiftd]

because the leds were connected in paralel.

 

[BT1324]

hey,
what do u guys mean by connectiing them parallel??

 

[shiftd]

in paralel: every positive lead connected to the other positive leads of the other leads and to the positive side of the battery. The negative lead also connnected to the - leads of the other leds and the battery.