Silly question about dress codes

commonreader especially...but anyone else is welcome to throw in their opinion too, of course.

Brad and I were just having an intense discussion about the definition of "smart casual". The dress code for the Capitol tour and reception tomorrow is labeled "smart casual". This is not a code we are very familiar with yet. So what does it mean? Can I wear a simple, summery, brown solid colored dress? I wore it to my cousin's wedding, but I dressed it up with jewelry and the wedding was VERY casual as wedding's go. The groomsmen didn't even wear ties, just sport coats and khakis. Anyway, the real discussion was about what that means for Brad. Does he need to wear a long sleeved, button down shirt? A tie? It is SOOOO hot right now, could he get away with a nice short sleeved, collared shirt? Just wondering....