I am a bit confused. If I print a part with 100% infill what is the point of a solid layer 100% infill is solid as it gets as far as I can see. Can the OP post a factory file from S3D? File > save factory file. Do this when you have everything set up as you want it to print so we can see all the setting and the model.
If you are seeing light you are under extruded..