Diffusion does:
-Spread the field; the heavier the diffusion the more it spreads the field.
-Soften shadows; the longer the throw, the more scattered the light and the softer the shadows become.
-Decrease the intensity of the illumination; the heavier the diffusion the greater the light loss.
On the other hand, diffusion does not convert a point source, like a Leko, to a linear source like a Kinoflo.
It seems to me that no matter how much diffusion you use in a point source, it’s very difficult to obscure textures and age lines. Linear sources and very large sources, like a large diameter Fresnel, do that best. Perhaps that’s why the “jewel” method of lighting, where you surround the subject with many sources, is so popular in Hollywood — it approximates a linear source. If the McCandless method with three points of light is good, then the jewel method with six or so points of light is excellent. Add diffusion and it becomes pure magic.
-From Richard Cadena's December Focus on Design article.
