One physicist asked whether ultraviolet light could be made safe for people. The answer is why this equipment exists.

Surgical site infections and drug-resistant bacteria.

Ultraviolet light has killed bacteria reliably since the 1930s. The obstacle was never whether it worked; it was that conventional germicidal UV at 254 nm damages human skin and eyes, so the room has to be empty. That makes it useless in exactly the places where infection actually spreads — an operating theatre during surgery, a filling line with operators on it, a waiting room full of people.

David Brenner's question was whether a shorter wavelength could keep the germicidal effect and lose the harm. Not shield people from the light — make the light itself unable to reach the living tissue.

Higgins Professor of Radiation Biophysics at Columbia University, and Director of its Center for Radiological Research. He read physics at Oxford, took his doctorate at Surrey, and began his career applying quantum mechanics to radiation therapy before turning to the biological effects of radiation at both ends of the dose scale — the very high doses of cancer treatment and the very low ones of everyday exposure.

Among his honours are Oxford's Weldon Prize and the Radiation Research Society's Failla Gold Medal. The far-UVC work began as a practical question from that low-dose research: whether there was a wavelength germicidal enough to be useful and short enough to be stopped by the dead outer layer of skin.