I ran across an old electronics book, the beginning chapters of which deal with light emitting diodes. it described the problem of blue LEDs; IIRC, the distance between the poles determines the color, but when you get them far enough apart to make blue light, current no longer flows between the poles.
Am I remembering correctly, and how was the problem solved?
It's the semiconductor bandgap, not the physical dimensions, that determines the color.
I think the Cree SiC blue led's predated these, but they were horrendously inefficient: they needed something like 3 volts, 50 mA to be a decent panel indicator. Paralleled 74S38s + 27 ohms from 5 volts!
But where do they use blue traffic lights?
John
The modern high-efficiency blue (and white) LEDs also require 3V, as determined by the band-gap voltage like you said. But they give more light at lower currents. These days all the rage is purple LEDs, for a much much more impressive light-color sensation.
Isn't purple needed for low-rider under-the-car lighting?
Every couple of years we have to write ECOs to change the current-limit resistors on a lot of our products that use blue LEDs. They keep getting more efficient, and customers complain that our front-panel lights are blinding them. We must average about 5 mA these days, down from 50 with the old Cree parts.
John
Must have been an old book, the problem was allways getting the right material to make them, now we have UV leds as well. The Xray led is still a way offf yet though.
By one man Shuji Nakamura
Adam
Austin,
Many things have changed since you were frozen in the 60's. And yes, Liberace was gay.
Bob
Japan, I think!
Blue plus yellow equals green...
Not that I ever saw.
Is that somehow better than using green?
John
Doubtful that it's "better", but...
(And never mind the fact that I brain-farted on the fact that we've had green LEDs seemingly forever - Was thinking in terms of "Damn... Only have red and yellow - Gotta "build" green if using LEDs, and the only way to do that is yellow plus blue.")
They cover too much of the visible spectrum to have any very saturated color at all.
Maybe this came from the Japanese having the same word for the colors blue and blue-green - something that I heard is true.
- Don Klipstein ( snipped-for-privacy@misty.com)
Ever mix the light from a blue LED with the light from a yellow one? It's certainly not green.
- Don Klipstein ( snipped-for-privacy@misty.com)
Can't say I have. To be honest, I don't think I recall ever even having a blue and a green LED in the same room together, let alone trying to mix 'em.
"Don Klipstein" a écrit dans le message de news: snipped-for-privacy@manx.misty.com...
I've hear they have brue-gleen reds too.
That is so; in the Japanese Language a 'green' traffic light is called 'blue' ["ao";"aoi"] while e.g. a 'green' leaf is 'green' ["midori";"midori no"]. As a result, a green traffic light and a blue LED are described by the same adjective which may be the source of this confusion - especially since the actual color of the traffic lights is identical to the western ones.
Chris
I once had some LEDs which gave all the colours of the rainbow including xray, I put them directly across the mains, WOW!!! I lost my cat the same night.
Gordon.
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