In order to learn how to light a scene properly it is helpful to first learn a few things about real lights. When you add a light to your scene you need to understand how to go about emulating the properties of the real light source that you want your Blender light to replicate.
The Properties of Real LightsEdit
Every light source always has a distinctive color of its own. A photograph taken at sunrise or sunset is very easy to distinguish from one that is taken at noon just by looking at the color of the light. Incandescent light bulbs emit a light of a color that is different from that of fluorescent light bulb. So a scene lit with one of the two will have a different color cast when compared to the other.
Light always streams in from a particular direction. The angle or direction of light has a particular influence on which planes of an object receive light and the shape and direction of the shadows that are cast by objects receiving light from that particular source.
Brightness and DecayEdit
As light travels through space it decays or grows dimmer with distance. Think of a firework bursting in the night sky. When the firework first bursts the sparks are bunched close to each other. Over a short period of time they quickly spread out from each other. If you replace sparks with photons of light and the firework with your light source than you have a very rough analogy to how and why light decays. All real lights decay with distance according to the inverse-square law. At times when lighting a Blender scene it becomes necessary to cheat this law.
Real lights will always cast a shadow of some sort. Real scenes also typically include multiple sources of light (even if these are only indirect lighting as a result of light bouncing off other objects). Thus, even in an area shadowed by one light source, there will typically be light coming from other directions, to soften the shadow so it is not completely inky black.
Real light sources rarely take the form of tiny points; the light usually comes from an area of discernible size. This manifests itself in the form of a softness to the edge of the shadows, or penumbra: areas behind an object where the light is partially obscured are less dark than the inner parts of the shadow where the light is completely blocked.
These are not all the properties of real lights, but as far as CGI lighting is concerned they are the most important. As we will see later on, Blender offers enough controls for you to tweak and adjust each of these key properties of light.