One of the key ingredients in the soup that makes a rendering look good is lighting. Lighting helps give a model depth through the use of highlights and shadows. Just as in the real world, objects that are closest to the light source appear the brightest and those the farthest away appear the darkest.
The two types of lighting in AutoCAD are default and user-defined. Default lighting, as its name suggests, is on and available in every drawing, and it's what gives some basic form to your 3D model when you click the Render button before you add lighting of your own. All types of user-defined lights can cast shadows. Most of the tools that you use to create and edit lights are located on the Lights and Sun & Location panels on the Render tab.
Over the past few years, AutoCAD's default lighting has improved in quality. Prior to AutoCAD 2007, default lighting consisted of a single distant light source, always directed toward the target of your current view from behind your back. AutoCAD 2007 added a second default light to help increase the lighting level, and to balance the lighting in a viewport.
Default lighting can't cast shadows, so I don't recommend using it for final renderings. It does work pretty well for quick conceptual renderings, however. You can control the brightness, contrast, and midtones levels for default lighting with the slider controls on the slideout of the Lights panel on the Render tab of Ribbon (see Figure 23-2).