Dixondale Farms lists Texas Super Sweet as a short day variety (see http://www.dixondalefarms.com/category/short_day_onions). Not sure if it is the same, but I would expect a variety having Texas in its name to be a short day.

TomNJ

If you got a Bonnie onion plant in Georgia, They label every thing "Sweets", but if you look on the end of the shipping crate they specify the cultivar. The only whites I have seen in this area from Bonnie are the White Granex hybrid, a short day cultivar.

Just think about the Land of the Midnight Sun Which is any land north of the Artic Circle. So that is Long Day. Gardeners use the Ohio River or Mason-Dixon Line as the divider for south and intermediate regions.
But it is night that counts not day. So If you are growing a plant Turn on a light for one hour at midnight if you want a summer growth response. Recall Crysantheums grow in the summer, but the long nights of fall trigger flowers. So when I want no flowers but lots of stem cuttings to sell during the spring, I turn on a hundred watt bulb every 8 feet apart each directions for an hour or two at midnight.
Harold Eddleman, Indiana Biolab. 30 miles west of Louisville KY