A light bulb is a device, a thing that was made specially to give out light.
Electric energy goes into the light bulb.
The light bulb then changes that electric energy into light.
If you look around your home, you will see light bulbs in lots of places, for example on the ceiling in the kitchen.
Look at the headlights on your car. Ask your parents if you can stand in a safe place where you can see the headlights when your Dad or Mam turns them on.
Is there a torch in your house? Turn it on. Shine the light into some dark places.
It was dark. Then the fluorescent bulbs were switched on.
The light bulb is giving out light.