Re: Blue LEDs? when did that happen?

From: Bullwinkle Jones (bullwinklejones_at_gmail.com)
Date: 09/29/04 

Date: Wed, 29 Sep 2004 03:37:11 GMT

Winfield Hill wrote:
> John Larkin wrote...
>>
>> Adam Aglionby <nws@capersville.co.uk> wrote:
>>
>>> guy-jin wrote ...
>>>> 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.
>>
>>> By one man Shuji Nakamura
>>> http://www.businessweek.com/1999/99_24/b3633068.htm
>>
>> 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!
>
> 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.
>
>> But where do they use blue traffic lights?

Japan, I think!

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