I have a added a cube and delete the top and bottom faces. And given plastic material. I have added a ico-sphere inside that cube and given emission light to it. I want the light should come out from the cube. I want to get the lantern effect. Image of lantern is attached. i want to achieve that effect. I have attach my blender file to know what material i have use.
The best looking result you can achieve by using Subsurface Scattering shader.
The other options could be also:
Mix Diffuse shader with Transparent shader - this will give you visible emission material trough it.
Translucent shader - the inside of the lantern will not be affected by light.
Diffuse mixed with Translucent - will be very close to Subsurface Scattering. You will want to mix it with Transparent shader.
Note that I've bumped Emission material to 20.