It's an either/or situation that can be confirmed with a test light or a voltmeter at the dimmer switch. That's why there are two filament connectors and one ground pin on a sealed beam bulb.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!