You may be on to something. I am using the correct bulb, it's a 13139 75 watt 12 volt. The voltage selector was set correctly, but when I change it to 220 volts the light dims noticably. Before I leave it at the 220 setting I just want to check that doing so is safe and won't damage anything. Am I correct that this is equivalent to using a dimmer and if anything will extend the life of the bulb? Thanks

Richard Wasserman