# Why can I put a resistor at either lead of this LED and still see its effects? [duplicate]

Just to add a little bit of context to the question, I am using an Arduino Uno and a breadboard.

I have a 5V power source running to the positive (longer) lead of an LED (rated at about 2v and 20mA). I then have a 150 Ohm resistor connecting to the negative (shorter) lead of the LED. The resistor is then connected to ground.

I am using a breadboard, so whenever I remove the resistor and connect it from the power source to the positive (longer) lead of the LED, I still see the same amount of resistance.

In other words, with no resistor, the LED is at X brightness. However, with a resistor attached to either lead of the LED, there is the same amount of resistance (thus, the LED is dimmer, at X÷resistance brightness.)

Based on my very limited knowledge of electronics, I would've assumed that you would have to connect the resistor to the power source, and then to the positive lead of the LED, so that the voltage and current would drop before they got to the LED. This seems to be false, based on my little "experiment" here.

Why is this the case?

• Tip: Learn the meaning of the word CIRCUIT Jul 3, 2014 at 18:36
• ^^^ LOL, bold and caps. Jul 3, 2014 at 19:00
• You can either lower the voltage before it the LED, or raise the voltage after the LED. Voltage is relative (between two points), so in either case the voltage ACROSS the LED (that is what is important for the LED) is reduced. (Actually it is the current that is reduced, but that is a next chapter.) Jul 3, 2014 at 20:45