Light bulbs get hot ! The heat is not a desired effect, and the light bulb is not very efficient, if you selected a light bulb to serve as a source of light. But if chose a light bulb to use in a place where you need heat, then the heat you get from it is very desirable, and the light bulb is very efficient. It all depends on your point of view.
The light bulb transfers electrical energy into light. What is one type of energy that is also generated that is NOT a desired effect? A) chemical B) heat C) mechanical D) sound