Ballast with lamp-diagnostic filament heating, and method therefor

A ballast (10) for powering one or more gas discharge lamps (30,40) includes an inverter (100), an output circuit (200), a filament heating control circuit (300), and a control circuit (500). During a lamp filament detection period prior to startup of inverter (100), control circuit (500) monitors a signal within output circuit (200) in order to determine the number of lamps with intact filaments that are present at the ballast output connections (202, 204, . . . , 210, 212). During a lamp type detection period following startup of inverter (100), control circuit (500) monitors a current within filament heating control circuit (300) in order to determine the type of lamp(s) present at ballast output connections (202, 204, . . . , 210, 212). The determinations as to the number of lamps and the type of lamps are utilized by control circuit (500) to provide an appropriate level of heating to the lamp filaments. Preferably, control circuit (500) is realized by a microcontroller that is programmed with data relating to the different lamp types that may be powered by ballast (10).