The Nagoya University Institute of Transformative Bio-Molecules (WPI-ITbM) research team of Designated Associate Professor Tsuyoshi Hirota, Postdoctoral Fellow Simon Miller, Professor Kenichiro Itami and graduate student Tsuyoshi Oshima (Research Fellowship for Young Scientists, JSPS), in collaboration with the group of Professor Ben Feringa and Postdoctoral Fellow Dušan Kolarski of Groningen University in the Netherlands, have achieved a world first: fully reversible manipulation of the period of the circadian clock using light, by exchanging part of a compound with a light-activated switch.