Machak, my Marinoni Ciclo, is a sport touring bicycle designed for things like randonneuring or light touring. I have done 1200K randonnees on him ... and I did a 3-month 5000 km cycling tour carrying approx. 40 lb of gear in 2 small panniers, handlebar bag, and Carradice. I probably pushed it a bit into the medium touring range, but the bicycle handled it just fine.

I would say that a bicycle designed for light touring should be able to go any distance you want to go ... and should be able to carry enough for a credit-card tour, or a tour where you opt to eat at cafes rather than bringing cooking gear, or maybe a tour where you go with a lightweight bivy and minimal sleeping equipment ... a tour where you don't carry everything and the kitchen sink.