dark/light

So yesterday i walk into class and i see 4 faces behind computers, illuminated by the eerie blue of their computer screens. All the lights were off. And i wasn't sure why. So i turned them on. i wouldn't take the time to say anything about it, except it's not the first time i've walked into the room and turned the lights on. It just doesn't quite make sense to me - why would you choose to sit in the dark when the light switch is just a few feet away?