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Blue LEDs? when did that happen?

G

guy-jin

Jan 1, 1970
0
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?
 
C

CBarn24050

Jan 1, 1970
0
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?

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.
 
A

Adam Aglionby

Jan 1, 1970
0
guy-jin said:
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?

By one man Shuji Nakamura

http://www.businessweek.com/1999/99_24/b3633068.htm

Adam
 
B

Bob

Jan 1, 1970
0
Austin,

Many things have changed since you were frozen in the 60's. And yes,
Liberace was gay.

Bob
 
J

John Larkin

Jan 1, 1970
0
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
 
W

Winfield Hill

Jan 1, 1970
0
John Larkin wrote...
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!

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?

Isn't purple needed for low-rider under-the-car lighting?
 
B

Bullwinkle Jones

Jan 1, 1970
0
Winfield said:
John Larkin wrote...

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.

Japan, I think!
 
J

John Larkin

Jan 1, 1970
0
John Larkin wrote...

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.

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
 
D

Don Bruder

Jan 1, 1970
0
John Larkin said:
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

Blue plus yellow equals green...
 
D

Don Bruder

Jan 1, 1970
0
John Larkin said:
Is that somehow better than using green?

Doubtful that it's "better", but... <shrug>

(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.")
 
D

Don Klipstein

Jan 1, 1970
0
Doubtful that it's "better", but... <shrug>

(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.")

Ever mix the light from a blue LED with the light from a yellow one?
It's certainly not green.

- Don Klipstein ([email protected])
 
J

John Popelish

Jan 1, 1970
0
Don said:
Ever mix the light from a blue LED with the light from a yellow one?
It's certainly not green.

They cover too much of the visible spectrum to have any very saturated
color at all.
 
C

Christoph Loew

Jan 1, 1970
0
Don said:
Maybe this came from the Japanese having the same word for the colors
blue and blue-green - something that I heard is true.

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
 
D

Don Bruder

Jan 1, 1970
0
Ever mix the light from a blue LED with the light from a yellow one?
It's certainly not green.

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.
 
G

Gordon Youd

Jan 1, 1970
0
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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