This episode covers the 1903 Nobel Prize in Physiology or Medicine, which was awarded to Niels Ryberg Finsen. The Nobel Assembly at the Karolinska Institute chose to give Finsen the award “in recognition of his contribution to the treatment of diseases, especially lupus vulgaris, with concentrated light radiation, whereby he has opened a new avenue for medical science.” Topics include Finsen’s use of phototherapy to cure skin infections, whether or not UV light can be used to fight coronavirus, and I use a Star Wars analogy to explain how photodynamic therapy kills cancer cells.