The typical headlamps weren't quite so powerful as the bulbs found in many of today's cars, but then neither were the 12-volt bulbs which were common throughout the 1960s. 45W (high beam) and 40W (low beam) wasn't unusual.
It was to keep the currents down that the auto industry made the move to 12 volts. It was a time when cars were starting to get a lot more accessories: Extra lighting, rear window defoggers, heater blowers, etc.
Remember too that in the mid-1950s cars also had dynamos rather than alternators, so there was little or no charge until the engine was revved above idle speed.
