We installed a new light fixture into our "old" (1930) bedroom ceiling. There was a ceiling fan there previously... Then we installed a dimmer switch; the kind that is NOT round...goes up and down. When we put the switch all the way up/brightest, the light starts to flicker. If we turn the switch down a bit it's ok, but not as bright. Is this a light fixture/wiring problem or dimmer switch problem? And is it something to worry about? Thanks for your help.