to answer the other question above, how much your switching on/off affects voltage at other fixtures depends. I have seen nightscaping transformers drop a full volt or more by adding 100 watts to a 500 watt trans that was only running 250 "bulb watts" to start with. I would say you have little to worry about on a quality multi tap torroidial trans running less than 70% load. as you go from 70-90% load you start to see some noticable volt drop across all taps. not matter the load, if you are switching on 180 watts, you will see some drop across all taps. it is easy enought to test by switching the commons on and off while you have your circuit tester handy at the trans. The greater problem is volting all your lamps properly with the switch on and then having premature burnout if the switch is usually off.