From: https://create.arduino.cc/editor/s09097/88945d49-f843-49b3-af38-803ff904df62/preview

An urgent light is used when there's no light

Things you will need:

Arduino

Computer

LED

Photoresistor

Resistors

Step 1: Step 1: Wire Up LED's

First, take 6 LED's out. I chose 2 green, 3 yellow and 1 red. You can change it if you like. Add a wire between the negative rail of the breadboard and the GND pin of the Arduino. Then plug the short leg of the LED into the negative rail of the breadboard. Then we need 6 resistors.