Since the beginning of this month there's a direct bus between Tainan and Foguangshan, which is good news for tourists into cultural attractions who'd rather skip downtown Kaohsiung. The bus is #8050, and - assuming traffic isn't unusually heavy - takes 1 hour 40 minutes one way (adult fare NTD207). It replaces the old #9122 service.
There are only six services per day. These leave Tainan TRA Station at 06.25, 09.10, 10.10, 14.10, 17.10 and 18.50. The route is quite scenic as it follows Road 182 through Neimen (venue of the Songjiang Battle Array), then Highway 3 into Qishan (where you can board a bus to Meinong). There's no need to change buses in Qishan; stay onboard for the few minutes it spends at Qishan's bus station. The final part of the journey, from Qishan to the monastery, takes less than 15 minutes. In the opposite direction, the first bus setting out from Foguangshan is at 06.15, the last at 16.45.