This seems much like the last project, and is similar in some ways. But this project uses a more complicated switching mechanism called a light-dependent resistor (LDR), also called a photoresistor.
The LDR changes its resistance based on how much light is hitting it at any given moment. We can use the Arduino to monitor how the resistance varies and map that resistance to a scale.
By setting "trip points" in the Arduino at certain points, we can tell the Arduino to turn something on or off based on how much light is hitting the LDR at any given moment.
Now that you've wired up a few projects, try to build this one just by looking at the diagram above.