page_title: H. J. Round
section_title: Light-emitting diode
hierarchical_section_title: H. J. Round / Light-emitting diode
caption_attribution_description: English: This image shows a replication of H.J. Round's experiments in which he discovered the effect underlying the light emitting diode (LED). A negatively charged needle contacts a positively charged crystal of silicon carbide or carborundum. At a voltage of 9 V and a current of 30 mA a green glow can be observed at the contact point between needle and crystal. A more detailed version of the setup can be found at www.dlip.de Français&#160;: Cette image montre une réplique des expériences de H.J. Rounds dans lesquelles il a découvert l'effet diode luminescente (LED). Une aiguille négativement chargée entre en contact avec un cristal positivement chargé de carbure ou de carborundum de silicium. À une tension de 9 V et à un courant de 30 mA on peut observer une lueur verte au point de contact entre l'aiguille et la goupille. Une version plus détaillée de l'installation peut être trouvée à http://www.dlip.de/?p=99
context_page_description: Captain Henry Joseph Round MC was an English engineer and one of the early pioneers of radio. He was the first to report observation of electroluminescence from a solid state diode, leading to the discovery of the light-emitting diode. He was a personal assistant to Guglielmo Marconi.
  Round was the eldest child of Joseph and Gertrude Round. He spent his early years in the small town of Kingswinford in Staffordshire and received his early education at Cheltenham Grammar School. He later attended the Royal College of Science, a constituent college of Imperial College London where he gained a first class honours degree.
  Round joined the Marconi Company in 1902; not long after Marconi had made his transatlantic wireless transmission. He was sent to the USA where he experimented with a variety of different aspects of radio technology, focusing on technologies such as powdered iron cored tuning inductors. He also performed some experiments with transmission paths over land and sea at different times of the day and investigated direction finding, for which he used a frame antenna.
context_section_description: In some later experiments with cat's whisker detectors using a variety of substances, he passed current through them and noticed that some gave off light – the first known report of the effect of the light-emitting diode (LED). Round published his result in 1907 in Electrical World:
  To the Editors of Electrical World:
  SIRS: – During an investigation of the unsymmetrical passage of current through a contact of carborundum and other substances a curious phenomenon was noted.  On applying a potential of 10 volts between two points on a crystal of carborundum, the crystal gave out a yellowish light.  Only one or two specimens could be found which gave a bright glow on such a low voltage, but with 110 volts a large number could be found to glow.  In some crystals only edges gave the light and others gave instead of a yellow light green, orange or blue.  In all cases tested the glow appears to come from the negative pole, a bright blue-green spark appearing at the positive pole.  In a single crystal, if contact is made near the center with the negative pole, and the positive pole is put in contact at any other place, only one section of the crystal will glow and that same section wherever the positive pole is placed.
  There seems to be some connection between the above effect and the e.m.f. produced by a junction of carborundum and another conductor when heated by a direct or alternating current; but the connection may be only secondary as an obvious explanation of the e.m.f. effect is the thermoelectric one.  The writer would be glad of references to any published account of an investigation of this or any allied phenomena.
  New York, N. Y.
  
  H. J. Round
caption: Recreation of the 1907 experiment by H. J. Round on the observation of electroluminescence from a point contact with a carborundum (silicon carbide) crystal.
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