Translucent sheeting is commonly used to create a “softer” light.
Harsh direct light is the enemy of jewelry photography.
While there are much better ways to make a soft, non-directional
lighting environment that is “friendly” to your images, putting a
diffuser over the direct light source is a convenient and marginally
BTW, the closer the diffusion is to the subject being photographed,
the softer the light, so diffusion right in front of the light source
is not a very good solution.
There are other problems associated with simply diffused light
sources for jewelry photography, but I hope the above answers your