Open a new default Blender document. Without doing anything else, hit F12 to render the default cube with the default settings. The result should look something like the image to the right.
Note the lower left visible face of the cube is completely black because the default light is at the upper right.
Go back from the render to the 3D view ( F11 ). Now select (with RMB ) the default light, and either delete it or move it to another layer (with M ). Go to your World tab in the Properties window, and look for the Environment Lighting panel:
Check the box next to the title, and leave the “E:” (energy) value at its default 1.0. This gives us a pervasive, directionless light, illuminating all objects equally from all directions, which means there will be no shadows. Do another render, and it should now look like the image to the right.
See how we have gone from inky-black shadows to no shadows at all. In the real world, lighting is almost never perfectly uniform, and this variation of light and shade is important to help us distinguish details of the scene around us. Without such variations, everything devolves into featureless blobs.
Now undo your deletion of the default lamp (or move it back to layer 1). Enable Environment Lighting again, but this time lower the Energy value to 0.1. Do another render, and it should now look like the image to the right. The shadowed face is still shadowed, but not enough to make it impossible to see any details it may have. This is usually the type of effect you want, unless you are aiming for really dramatic contrasts.
So the lesson is:
As you learn more, you will find that it is common to use two or three lights, or even more, to ensure proper illumination of a scene. In simple tutorials, where no explicit details are given about lighting, you can probably get by with the default light, plus some environment lighting (as we added earlier) to soften the shadows.