Actually there is a good way of controlling AC Voltage.
If you connect an ac load to ac part of bridge rectifier.
Then if + and - of bridge is shorted together, then full ac waveform would appear across load.
If short is removed then no current will flow though load.
What you need to do is switch FET on at each zero crossing,then switch FET off after a period of time between 4 and 9 ms on each cycle.
Microcontrollers e.g. 8 pin 12F series are ideal for the job.
Since FET is connected to + and -, then it sees only DC.
Note: If using an inductive type load, then you must connect a suitable AC rated capacitor (e.g) type in some types of fluorescent lights, or AC motor absorption caps in parallel with the load. This type of circuit will work on mains, but FET and cap must be suitably rated. Most of all be careful! Mains can kill. You must be fully competent to work with mains if not get help form some one who is!