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I'm not talking about the onboard LED at the Arduino board here. What those LED's mean, is the LED's we usually plug at the breadboard.

I plugged in a yellow LED and a green LED onto a breadboard. I wired it up, and noticed something. Green LED lights up at its full brightness, while yellow LED didn't emit any light. Tried in another yellow LED, and it seems like it's smoking, which means it's burned.

I'm not using a 220 Ohm resistor or any kind of resistor that time. I also have no idea why the green LED didn't burn itself, when you plug it directly on 5V and GND. I'm expecting that the green LED should also be burned, because I think, that's the way how LED's work.

When I plugged the green LED into a 220 Ohm resistor, it did as expected. It lowered its brightness, of course, because the resistor is resisting some of the electricity to pass on the LED.

closed as off-topic by user31481, Michel Keijzers, gre_gor, jfpoilpret, per1234 Nov 24 '17 at 23:23

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question does not appear to be about Arduino, within the scope defined in the help center." – Michel Keijzers, gre_gor, jfpoilpret, per1234
If this question can be reworded to fit the rules in the help center, please edit the question.

  • And the question is? – user31481 Nov 24 '17 at 11:09
  • I don't see the Arduino connection here. Or a question. – sempaiscuba Nov 24 '17 at 11:10
  • The Arduino Uno can give 40mA shortcut current with a digital output pin. Maybe that was not enough to burn the led. I think that somewhere along the line from the computer via the usb cable, the Arduino board and the output pin, the current or voltage was lowered or the internal resistance of the led is higher or became higher during burning. Try a power supply of 5V 2A and connect all the leds to burn them all. What is the point of this? If you want to know about leds then measure the voltage and the current of the led. Can you get rid of that Arduino board, it might no longer be reliable. – Jot Nov 24 '17 at 11:11
  • @LookAlterno Oh, sorry. I forgot to include the question. The question is, "Why is the yellow LED burning, while the green LED is not?" – Lloyd Dominic Nov 24 '17 at 11:13
  • @sempaiscuba I'm just new to the community. If you like, then you can move this question / post to a different Q&A site. – Lloyd Dominic Nov 24 '17 at 11:14
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I'm not using a 220 Ohm resistor or any kind of resistor that time.

Well, there you go then. If you abuse an LED you can expect it to die.

When I plugged the green LED into a 220 Ohm resistor, it did as expected. It lowered its brightness, of course, because the resistor is resisting some of the electricity to pass on the LED.

And the LED was so much happier when you weren't abusing it.

I'm expecting that the green LED should also be burned, because I think, that's the way how LED's work.

It was probably tinged with yellow. And if you left it a while it would get yellower as it got hotter, and then started to fade out, and eventually die.

Different LEDs use different combinations of elements to make the different colours. Different types of the same colour also use different elements. Old fashioned green LEDs are more reliable, though dimmer, than newer ones. They withstand more abuse. But they will still complain after a while.

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Majenko already mentioned the reason. Maybe it's good to add that different colored LEDs (and even each type/model) should have its 'calculated' resistor.

Find the forward voltage of the LED (differs per type/color), and use the following formula :

V - Vfv = I * R  <=> R = (V - Vfv) / I

E.g. if the forward voltage is 2V and you use a 5V Arduino and want 20 mA:

R = (5 - 2) / 0.02 = 150 ohm

The maximum mA you can find also in the data sheet of the LED.

  • Would be much better if you give the meaning behind those acronyms. (What is "V" ?, what is "Vfv" ?, etc. ...) – Lloyd Dominic Nov 24 '17 at 11:17
  • @LloydDominic If you don't know what V (voltage) means, or what Vfv (Forward Voltage) means, your better stop playing with electricity before you kill yourself or burn down your house. – user31481 Nov 24 '17 at 11:20
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    If someone does not know what V or Vfv (forward voltage) means, I think he should either google it or ask a new question. – Michel Keijzers Nov 24 '17 at 11:22
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I'm expecting that the green LED should also be burned, because I think, that's the way how LED's work.

LEDs get burned from excessive heat that is the result of excessive current. Green LEDs have higher forward voltage than yellow LEDs so, if everything else is equal, the "excessive" current through the green LED is smaller than the one through the yellow LED, thus causing the yellow LED to warm up faster and thus burn out faster.

Other factors may still attribute to the yellow's burn-out.

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