The Sun is such a famihar companion that many people forget that sunhght is a prerequisite for Hfe on Earth. Do we fully realize that conversion of the almost inexhaustible solar photon energy into free oxygen and fuel by the plant kingdom is the basic pathway by which we survive on our planet? Also, do we fully understand that conversion of light signals into electrochemical energy enables us to see ? Paradoxically, whereas light is life, the endless creativity of man's brain in many areas of science has led us in the past decade to the recognition that certain rays of sunlight can become the fatal Trojan horse to living species.