According to a recently released German study, the supposed "environmentally friendly" compact fluorescent light bulbs (CFL's), are reported to have "cancer causing chemicals" that are sent out when the light is switched on, reports London's Daily Telegraph: Their report advises that the bulbs should not be left on for extended periods, particularly near someone’s head, as they emit poisonous materials when switched on. Peter Braun, who carried out the tests at the Berlin's Alab Laboratory, said: “For such carcinogenic substances it is important they are kept as far away as possible from the human environment.”