In dystopian films, it is a common trope to depict the sky as filled with a thick fog, blocking the sun's rays and bringing a dark atmosphere to the scenes. Whether in Blade Runner or in a Black Mirror episode, the lack of sun commonly represents a future we would rather not live in. The sun provides heat to planet Earth and is a great source of light energy, essential for the survival of many living creatures. We can generate electricity from the sun and still use only a fraction of the energy it provides. Sunlight also regulates our circadian cycle, which affects our mood. But recent forest fires and industrial pollution in some large cities have already made the dystopian blockage of sun a relatively common phenomenon, depriving hours of sunshine from many inhabitants. Concurrently, with the COVID-19 pandemic, we are living a plot that few science fiction writers could have predicted, and new technologies and solutions have emerged to try to contain the spread of this invisible enemy. Can the sun, or specifically ultraviolet radiation, kill viruses and bacteria? Could it kill the coronavirus?
The answer is not a straightforward one. It has been proven that the sun can kill some viruses exposed for a long enough time; environments that receive solar radiation for a few hours experience less humidity, which prevents the proliferation of fungi and bacteria. Ultraviolet radiation is responsible for this phenomenon. Compared to the visible light that we can see with our eyes, ultraviolet (UV) has a higher light frequency. That's where the name comes from: because violet is the highest frequency color that the human eye can perceive, ultra-violet light sits between visible light and X-rays on the spectrum.
