Light is nearly as important to land dwelling life as water. Our bodies create some nutrients by sunlight, like vitamin D. Plants that are needed to feed us and animals need sunlight to grow. Without light life would not be as we know it.
Why is light important to people?
without light we wouldn't be able to see.
While you're in your house, turn all the lights off at 2 PM. Your answer is there.
If you couldn't find it, then try to live your life one week this way. Then surely you'll reach your answer. (specially in the bathroom)
Everything is speeded up light.