Ever tried to buy a 240v light bulb...not in your everyday store! If they had a bulb, oven light, night light, indicator light, etc., they were powered off 110. When I was in the Army, we had one shelter with both 28vdc and 110vac lighting. The bulbs were the same style. If you weren't careful, the 28V bulbs work great as flash bulbs! Working the other way, they worked more like a candle, which isn't catastrophic, but kind of useless.