All light bulbs eventually burn out. Some are just in harder to reach areas when they need to be changed. If your Sharp brand microwave's light is out, you can change it on your own, there's no need to take it to a repair shop. The light bulb is needed to see the inside of the microwave when you open it and the food inside while it is running.
Turn off the microwave and unplug it from the electrical socket.
Unscrew and take off the outer cover of the microwave. The screws are located at each corner.
Unscrew the cover over the light bulb.
Replace the bulb inside.
Replace the light bulb cover and the outer cover of the microwave.
Plug the microwave back in and open the door to test the bulb.