Just as it is obvious that in most daylight scenarios the Sun will be the dominant and therefore key light, it is also very clear that without the secondary or Fill light that comes from the Sky, what we call "natural daylight" would probably not look so natural at all.

Essentially the Sky acts as a giant diffuse reflector that is able to cast at least some level of illumination even into areas of an environment that direct Sunlight could never hope to reach. In this respect, the Sun & Sky system form a perfect lighting partnership—one that we often fail to fully appreciate for both its technical complexity as well as its aesthetic beauty.

Besides adding almost perfect illumination coverage for an environment, we also need to take into account the fact that Skylight can and often does add quite a strong color cast. Again this is not something that we generally appreciate or possibly even notice due to the automatic color balancing that our eyes and brain typically...