No, this is nothing biblical. It's about roof lights. You might never have seen one, if you live in the city center. They aren't popular amongst apartment houses, they're more of a private house thing. During sunny days, wouldn't you like to let some of the light in from outside? Well, you can't do that with a closed roof, you need Roof Lights! There are many types of them, and they serve many purposes. You can have round ones, oval ones, rectangular or triangular ones - all kinds! And you can look at them yourself at www.coxbp.com. And here are several functions, the roof lights they offer execute.
1) Light. The sun always shines above our heads, providing us with warmth and light. However, we do not always appreciate that, as we live under thick slabs of concrete and bricks. So why not get in touch with mother nature? Instead of burning the light bulb all day, get a roof light - the light will be much more pleasant and cheap! Free, actually! And it can't get any darker than the ceiling, which, let me remind you, lets in no light at all.
2) Warmth. As the roof light lets in sunlight, warmth also comes. Though you may not want it, I'd say it's acceptable at least. Roof lights are made from special glass, for this purpose. You wouldn't want cold coming in, would you? Come to think of it, I don't know whether roof lights are a good idea for a house in the northern parts. Sure, the glass is strong and waterproof, but tens of pounds of snow on it are bound to get the air pretty cold.
3) Visibility. Sure, this isn't much, but it sure is pleasant to see the blue skies from the comfort of your own home. And during rainy days, you could watch rain drops, falling on the glass. Or snow flakes, for that matter. And don't be afraid, the glass is surely strong enough to support the weight and pressure.
But what about some theoretical uses for roof lights? I assume you could make them into solar batteries, or rain water collectors - for that post-apocalyptic fan, that I'm sure you'd find inside yourself. So put some diversity in your home with roof lights!