Is it night?

Tonight as I was getting dinner ready, Will popped his head out of the bathroom to ask me if it was night or day. I replied yes and went back to what I was doing. When Will came out of the bathroom later, I asked why he needed to know if it was night or day. He looked at me like I was crazy and replied, "Because if it's night, I can take my underwear off. I don't need underwear in the dark!" Of course, why didn't I think of that?