When I connect the LED's in parallel, and with a resistor in series with the voltage source, I noticed that not all of them light up, just the first ones.
Wouldn't theoretically all of them light up because they all are in parallel and have the same voltage?

Thanks in advance.

 

All leds are not created equal. Some require higher voltages than others. What voltage are you using, and what color leds are you using?

 

Even with a common batch off the same die there will be variations. Manufacters test large batches and group similar LEDs in lots, which is not practical for home use.

LEDs, 555s, Flashers, and Light Chasers

 

We tell people every week that Light Emitting Diodes are not light bulbs, they are not resistors, they are diodes. Diodes have a break over voltage and they are not exactly the same from one diode to the next. The diode with the lowest break over voltage will hog the current. Sometimes it can't hog all the current before the next lowest voltage diode starts to break over into conduction, so a few will light up, but it never ends well unless you can make matched sets like Bill talked about.

 

All leds are not created equal. Some require higher voltages than others. What voltage are you using, and what color leds are you using?

they are all Red LED's and I'm using a 9V battery in series with a 470 ohm resistor.

 

Even with a common batch off the same die there will be variations. Manufacters test large batches and group similar LEDs in lots, which is not practical for home use.

LEDs, 555s, Flashers, and Light Chasers

That was very helpful, thanks.