Xref: utzoo sci.electronics:3848 rec.audio:8350
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!lll-tis!lll-winken!ubvax!ardent!sleat
From: sleat@ardent.UUCP (Michael Sleator)
Newsgroups: sci.electronics,rec.audio
Subject: Re: Looking for Blue LEDs
Keywords: blue blue blue, not yellow or red or green
Message-ID: <595@ardent.UUCP>
Date: 21 Sep 88 01:35:34 GMT
References: <1138@nmtsun.nmt.edu> <862@ritcv.UUCP>
Reply-To: sleat@ardent.UUCP (Michael Sleator)
Organization: Ardent Computer
Lines: 30

In article <862@ritcv.UUCP> cep4478@ritcv.UUCP (Christopher E. Piggott) writes:
>
>I'm pretty sure DigiKey, Inc. sells them -- check 800 information for a good
>number on them.  (1-800-555-1212).
>
>I have several, but have no idea where they came from.  (They look more
>purplish than blue to me, as if they were red L.E.D.'s with blue paint
>mixed into the glass.  I have technical reasons to suspect this, also: they
>are not as grossly enefficient as blue L.E.D.'s should theoretically be).

Um, wait a minute...

Although not as narrow as a laser diode, LEDs have a reasonably narrow
output spectrum.  This means that a red LED emits almost all of its energy
at the red end of the spectrum.  All that blue pigment in the plastic
would do is absorb non-blue light.  If there were a significant amount of
blue light in the original output, then blue pigment would indeed make it
look more blueish (shades of Yellow Submarine...), but then the unfiltered
LED would look rather magenta-ish, no?  Since to my eyes regular red LEDs
don't look magenta, I suspect that trying to make a blue LED by throwing
away all of the red light from a red LED would be *very* enefficient.
(Ever hear of a "DED"?)  A quick check with a handy chunk of Lucite acting
as a prism doesn't show any significant blue emission from the LEDs on the
back of my Sun-3/50.

Of course, if you're suggesting a florescent pigment that absorbs red and
emits blue, that's another matter.  I doubt that's what's going on, though.

Michael Sleator
Ardent Computer
...!uunet!ardent!sleat