Looking at the light source itself through the diffusion we can clearly see how a combination of direct light and diffuse light creates a harder source (as in the Spun and Opal options). As the definition of the original light source becomes increasingly obfuscated by the diffusion material, the overall size of the source increases and the quality of light is softened substantially.
The Tough Spun has very interesting properties. As it is a fine pattern of thin threads, there are clear spots along the material where direct light can shine through. This means that it produces a combination of both hard and diffuse light. You can see this illustrated in the images of the geometric shapes from our test, as both the umbra and penumbra of the shadows are well-defined.http://www.lxglassfibre.com/grid-cloth/