Over the years I have used a number of fakes, cheats and workarounds. Some I have used because there wasn't a tool or option coded yet and some because it was either easier to use the fake or because it saved render time.
Of all the fakes I have used (or read about), my favorite has always been the "Light gel", used to create interesting shadows. Light gels have been used in traditional photography and film making almost since their beginnings.
So just what is a "Light gel"? In traditional photography and film making, the term applies to sheets of acetate (or other similar clear materials) with patterns printed on them, such as bars, window panes, leaves etc. The light gel is then held in front of the specified lamp or light source to create the shadow patterns. (Light gels can alos be colored to create moods or colored shadows.)
In Blender, this technique is easy to apply and doing so can save not only on modeling and set up time, but it can save quite a bit on your final render time.
So just how do you go about setting this up?
To create light gels in Blender, you simply add textures to your lamps. It's really that simple. You can use either procedural textures or images (grayscale seems to worque best.)
You set up Lamp textures the same way you do for materials, (in the Texture buttons [F6]). Some fun texture types to try are “Wood” and “Clouds”. Both add great shadow patterns. You can experiment with the other texture types to create more unusual patterns.
To create somewhat more realistic shadow patterns, of say, tree branches and or leaves, you can use a grayscale photo. Then when applying the texture to the Lamp, choose Image as the texture type and pik your grayscale photo. Instant shadows.