We just returned from the Radiance, and we saw a little bit of everything on Smart Casual night. From nice long sleeve sport shirts to jackets with open collar. Didn't see many ties. I wore a jacket, a button down oxford, and dress slacks...seemed to work great. It was nice to be able to break out a summer weight jacket for dinner, and I was glad I didn't have to wear a tie.
Hope this helps....have a great time on your cruise!