you may want to take a look at some real world ideas and then see how they translate into the scenes you want to create

http://www.mediacollege.com/lighting/

after that the question is one of those how long is a piece of string type thing, it depends on whether you doing an indoor / outdoor scene, day / night, high realism versus slower render, etc etc.

Please give us a few more clues about what you hope to achieve and we can help more.

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Toolset: Blender, GIMP, Indigo Render, LuxRender, TopMod, Knotplot, Ivy Gen, Plant Studio.