If we want to light up an LED, a right resistor is a must. If we do a lot of electronics projects, we’re likely to have dozens of resistors lying around. If we are just green hand, an assortment might need to be prepared. Resistors also come rated to handle varying amounts of power. Higher rated power resistors are able to safely dissipate more heat generated.

We know Ohm’s Law formula is V = I × R, where V is the voltage, I is the current, and R is the resistance. To get the V in our formula, we need to know the voltage of our power supply, and the voltage of our LEDs. Resistors are usually available in all kinds of resistance value, tolerance and power. 1/4 watt resistors are probably the most common, and are generally just fine for simple LED circuits like the ones we’re covering here.


We can calculated the resistance values and use a resistor with a ±5% tolerance, so it won’t necessarily be exactly that value anyway. To be on the safe side, we generally select the next higher value that we have on hand.

Lets hook this up:
3 V battery box, 51 Ω resistor, and yellow LED.



Now, that’s a nice little LED circuit, but how can we do this with more LEDs? Can we just add another resistor and another LED? Well, yes, to a point. Each LED will want 25 mA, so we need to figure out how much current our batteries can source.

Finally, let us note that in this article we’ve been talking about your basic through-hole, low-power LED. Specialized types like high power LEDs may have somewhat different features and requirements.