You are presented with the quiz "In order to operate at night, solar-powered LED lights require what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "alight bulb requires electrical energy to produce light" and "solar-powered lights that use LED bulbs provide the most efficient and most hours of light at night". 

So, what's the best answer to the question?


 

       electrical energy    