LED Lights and Electricity

In this example we are going to build the simplest useful electrical circuit – we are going to make electric light.  This may seem a simple task but we will actually cover many fundamental ideas about electrical circuits that are important as we build much more complex machines.

This is the first in a series of sparks that take you from building this very simple circuit to building a machine that uses software (code) to control hardware (things in the world).

This first step is made to understand the hardware stuff so we can then understand what the software has to ‘do’ to make stuff happen in the real world. We will quickly move from this simple circuit to controlling circuits using code.

This spark is a practical experiment exploring the electrical concepts described on the other side of this link. You should read up on them first.

For this first step you will need;

  • a 220 Ohm resistor (resistor spark)
  • an LED of any colour.
  • a 9V battery.

LED – Light Emitting Diode. 


A light emitting diode is just a little light. Because its a diode electricity only passes through it one way. It always pass from the long leg to the short leg. When electricity passes through the diode it lights up.

Unfortunately the LED can only take so much current before it breaks and stops lighting up. So we need something to reduce the current flowing through the diode.

Learn more about why? this is the case over here: Electricity and Circuits 101.

For that we need a resistor.


Now grab a 9V battery the resistor and the LED and try this:

With the battery in front of you, hold the LED in one hand and the resistor in the other.
Hold the short leg of the LED in the large negative terminal of the battery.
With the other hand hold one end of the resistor to the positive terminal.

With the other end of the resistor  touch the long leg of the LED.


If you were successful your LED lit up. Congratulations you’ve made your first electrical circuit.


Here we are using a resistor to restrict the amount of electricity (of current) that moves into the LED light. If we just connected the LED  to each terminal of the battery there would be too much current and the LED would break.

Its a little like  we had a waterwheel on the dam – if there was too much water the wheel would move too quickly and break – we need to restrict the current so the wheel turns at a safe speed – we use a resistor to do that.