The world was darker and more rural in 1928, and the few streetlights that existed were pretty dim in themselves. Relatively, 21cp was adequate for most night driving at Model A speeds of 25-35 mph, and still is, when you get out of the city glare, get your night vision adjusted, and don't overdrive your lights. Remember there was hardly any electricity at all in the rural south until about 1938 when the TVA started damming rivers and stringing wires. Even now, if you can get away from the city glare and out into real country, it's surprising how well you can see by nothing more than starlight, and you can practically read by a full moon.