Good question!!! However, its the wrong question. It is common knowledge that the light is there to help you see anytime. Do we open the refrigerator door only at night? I don't think so!!! So, I have to ask another question: Since the questioner already knows the answer: What was the question they should have asked in the first place? Jesus faced a similar problem with the Sadducees...
WEB: Matthew Chapter 22
 On that day Sadducees (those who say that there is no resurrection) came to him. They asked him,  saying, “Teacher, Moses said, ‘If a man dies, having no children, his brother shall marry his wife, and raise up seed for his brother.’  Now there were with us seven brothers. The first married and died, and having no seed left his wife to his brother.  In the same way, the second also, and the third, to the seventh.  After them all, the woman died.  In the resurrection therefore, whose wife will she be of the seven? For they all had her.”
 But Jesus answered them, "“You are mistaken, not knowing the Scriptures, nor the power of God.  For in the resurrection they neither marry, nor are given in marriage, but are like God’s angels in heaven.  But concerning the resurrection of the dead, haven’t you read that which was spoken to you by God, saying,  ‘I am the God of Abraham, and the God of Isaac, and the God of Jacob?’ God is not the God of the dead, but of the living.”"
I am a little surprised at Jesus. He certainly must have known what the Sadducees believed and yet he answers their question anyway. Further, he just says they are mistaken and do not know the Scriptures or God's power. Frankly, I expected a much harsher interaction with the Sadducees. I can only guess that some of them were honest in their misunderstanding and Jesus knew that some of them would listen to the truth. But, it seems also quite certain that some of them were just trying to trick him into saying something they thought they could easily refute. I guess the "why" Jesus answered as he did is not as important as the "answer", but the concept that is the result of the exchange is priceless. To know the nature of life after life is understood by knowing God and perhaps that was the point of it all anyway. God desires life for us and NOT death and the life that HE has in mind for us is so wonderful, so different, that its almost beyond description. For, it is a life in HIS PRESENCE, with HIM!!! Wow, makes you almost want to be there now, doesn't it??? So, perhaps good can come from bad after all??? Only one thing remains for this post and that is to answer the refrigerator question that started all this. Why are you worrying about a light in a refrigerator when you should be asking WHY you are having midnight snacks in the first place? This means you, Gary! Stop thinking about food already and finish the post!!!