Interesting. Carbon arc-lamps were used in movie theaters. I was lucky to visit the projection booth in my hometown theater and got to see the carbon arc in action behind the heavily tinted door. I'm told they changed rods between movies, so they did not last long. I think Xenon bulbs replaced them sometime in the 1960s. I think the voltage had to be DC, but I forgot how many volts.
But yes, it was "make do" technology until something better came along.
