We selected one of our Philip Watts vision panels for our showroom door so we looked a bit more inviting on the darker days. We think it works. We sell these in all shapes and sizes. http://www.cheshirehardware.com/catalogsearch/result/?q=watts+port

Philip Watts port holes for doors going up on the site today. Some amazing vision panel designs! Our simple circular one was installed at the showroom today.