Uploaded December 2024 | Updated September 2026, 2 weeks ago
In this video I relate the story of when the LED effect was first seen.
Today we use them for all sorts of things from panel indicator lamps, through numeric and alphanumeric displays to backlights for TVs, lighting and much more.
The effect was first noticed when one of Marconi's engineers, a brilliant man called Henry J Round was experimenting with the Cat's Whisker detectors of the day. He discoved that if he passed current thought it, then for some substances a small light was emitted
He reported this in a publication of the day called Electrical World and it was published in 1907 - so after all they are not such new devices.
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 11 volts a large number could be found to glow. In some crystals only the edges gave the light and others gave instead 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 centre 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 the 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.
H. J. Round
Or on my website at: electronics-notes.com/articles/history/semiconductors/light-emitting-diode-led-history.php
Website homepage: electronics-notes.com
Please don't forget to subscribe to our YouTube channel: youtube.com/electronicsnotes?sub_confirmation=1
In this video I relate the story of when the LED effect was first seen.
Today we use them for all sorts of things from panel indicator lamps, through numeric and alphanumeric displays to backlights for TVs, lighting and much more.
The effect was first noticed when one of Marconi's engineers, a brilliant man called Henry J Round was experimenting with the Cat's Whisker detectors of the day. He discoved that if he passed current thought it, then for some substances a small light was emitted
He reported this in a publication of the day called Electrical World and it was published in 1907 - so after all they are not such new devices.
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 11 volts a large number could be found to glow. In some crystals only the edges gave the light and others gave instead 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 centre 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 the 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.
H. J. Round
Or on my website at: electronics-notes.com/articles/history/semiconductors/light-emitting-diode-led-history.php
Website homepage: electronics-notes.com
Please don't forget to subscribe to our YouTube channel: youtube.com/electronicsnotes?sub_confirmation=1
