Hard Lighting
When you use hard lighting, strong shadows, that really show the details of a picture are made. In hard lighting there is only a small bit of light that makes sharp lines (shadows), and it shows very high contrast. Hard lighting also really makes the viewer focus on the focal point that has the only light, because everything else around the focal point is dark, and can't be seen. If you're using natural light, most people try to underexpose the light so they can get the shadows, and also when using hard lighting, it is said that the light should be small and relatively far away from the subject. Also, depending on how you want the photo to look you can position your light source directly on the subject or off to the side. For a single light source when taking a photo with hard lighting, you usually set a main light behind the subject and maybe to the side a little bit. You can adjust the brightness to your liking, and move it around to make the shadows be where you want them.
Classic Lighting
Butterfly Lighting
Loop Lighting
Profile
Rim Lighting
Split Lighting
Rembrandt Lighting
Enhanced Photos