“A well documented application of light to healing, which was rewarded with a Nobel Prize, is red light therapy applied to the treatment of smallpox and tuberculosis. Niels Ryberg Finsen suffered from an illness now called Pick’s disease, which is characterized by progressive thickening of the connective tissue of certain membranes in the liver, the heart, and the spleen. Having a great interest in the healing power of the sun, he conducted studies both in the laboratory and thorough clinical experiments, adopting a procedure very similar to the one used today to find applications of lasers in medicine. The fact that he did not know the details of the light-tissue interaction in the laboratory did not prevent him from using light in clinical applications. He devised the treatment of smallpox in red light (1893) and the treatment of lupus (1895) and was recognized with the Nobel Prize in 1903. In beautiful but simple experiments Finsen demonstrated that rays from the sun or from an electric arc may have a stimulating effect on tissues. If the irradiation is too strong, however, it may give rise to tissue damage. It is the same fine line that medical applications of lasers need to walk on.”