Need more natural light? Put a skylight in the roof. During cool weather, it's great.
But then when summer hits, suddenly the skylight is beaming unbearable heat into the room. Extreme example: I once worked for a couple who had bought a modernistic two-story house with a glass-roofed atrium in the center. From April through November, their atrium was unbearably hot and steamy.
So what's the solution?
Pretty easy: Let the sun work for you. Think about it. You want the sun's heat in the winter but not in the summer. So instead of a glass-topped skylight, think about this: Build a shaft where you'd otherwise put a skylight. Build it up three feet or so above roof-level. Put a south-facing window in it. Now your room will drink in sunlight (and some heat) all winter long. Then, as spring advances, at some point (depending on the exact design of your skylight-shaft), the sun, as it advances northward, will no longer shine directly in, though you will still get indirect light. Then, in the fall, as the weather cools, the sun will move southward again and will one day shine directly in again.
As for the couple with the atrium, I didn't know the solution then, though I do now. We should have built a roof -- perhaps sloping up toward the south -- over the whole atrium, and installed a large window in the large south-facing side. And this would have accomplished exactly the right effect: it would have screened out the summer sun and admitted lots of winter sun.
One more (important) detail: that south-facing window should not be the standard sort used everywhere these days, the insulated, low-E argon-filled double-paned glass, which essentially blocks both sunlight and heat. Instead it should be glass which admits maximum sunlight (technically called "high solar heat-gain constant" or high SHGC) and also is insulated to keep heat in in the winter and to keep heat out in the summer (technically called low-U).
Double-paned ordinary glass (not low-E or argon-filled) actually is fairly high SHGC, but is a poor insulator, so that even though you let in the winter sun, you will lose a lot of heat -- and even though you block the summer sun, you will let in a lot of summer heat just from the air.
PPG makes several lines of glass called Sungate, which do just what is needed: they let in lots of sunlight (so use this glass only facing south) but block unwanted heat loss or gain. It costs a little more than ordinary glass, but would be an excellent investment.
