Since the very beginnings of humanity sunlight has been attributed with the ability to prevent the spread of infections.

Without a serious explanation for this fact it has been proven in later research, that a bacteria killing effect of the invisible share of sun rays proceeds from below 320 nm.

Even at the end of the 19th century (!) the first artificial UVC ray sources were developed and used. An effective form of disinfecting without using chemicals or very high temperatures since then was available.