VOLKER STEGER / SIEMENS / SCIENCE PHOTO LIBRARY VOLKER STEGER / SIEMENS / SCIENCE PHOTO LIBRARY
Testing fluorescent light tubes. Researcher testing the endurance of fluorescent light tubes. These lights are more efficient than filament light bulbs as less of the radiation is in the infrared. The electric current passed through the low pressure mercury vapour in each tube causes the mercury to emit ultraviolet radiation. This is re-emitted as visible light by the phosphors on the inside of the tube. Phosphors, substances that emit light without being heated, are chosen so that the whole light spectrum is emitted, produc- ing white light. Photographed at Siemens' Osram Sylvania Laboratory, Beverly, Massachusetts, USA.
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