Hmm I've had the front end off my car and all the lights out more than once but never took a close look at the sealed beams. I just checked and my outer two are Sylvania halogen. Not the kind that one can just replace the little bulb, it's built like a regular sealed beam but has the little halogen bulb inside. The driver's inner has T3 on it and the passenger inner just says General Electric. Don't know why one couldn't change just one over. Some of the more powerful headlights have to have ceramic sockets, the plastic ones melt from the heat.