Images Dated 25th September 2002

View of a man holding a blue light emitting diode

Blue diode. View of a man holding the world's first marketed blue light emitting diode (LED). He is holding the diode to his face. The only blue LEDs available before this were based on silicon carbide. These were very inefficient and did not glow very brightly. LEDs are made of two thin film layers that contain specific impurities which give them opposite electrical properties. An electric current passing through the LED will make it produce light. LEDs were developed in the 1960s but could initially only produce red or green light. In 1995 the Nichia corporation of Japan first marketed these blue LEDs

© VOLKER STEGER/SCIENCE PHOTO LIBRARY