Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!tektronix!tekgen!tekigm2!neals
From: neals@tekigm2.TEK.COM (Neal Sedell)
Newsgroups: sci.electronics
Subject: Re: speaking of LEDs
Message-ID: <3593@tekigm2.TEK.COM>
Date: 4 Oct 88 20:35:12 GMT
References: <1988Oct2.053515.18004@utzoo.uucp> <1652@eos.UUCP>
Reply-To: neals@tekigm2.TEK.COM (Neal Sedell)
Organization: Tektronix, Inc., Vancouver, USA
Lines: 24

Sorry to transpose this response with another article, but our mailer
has been extremely brain-damaged for quite a while now.  It used to be
almost perfect and I felt sorry for those less fortunate...

>>Some cave-explorer friends are experimenting with the new LEDs for 
>>emergency light sources:  Two LEDs, each in series with a 33-ohm 
>>resistor, connected to two alkaline AA-cells, will make enough light 
>>to get out of the cave, for 24 hours.  
>
>Why not connect the two LEDs in series and use a smaller resistor.

Well, since we're talking about an emergency light source, the key-word
is RELIABILITY, not efficiency!

>Answer of sorts to the question above:  the forward drop across the LED
>is too great.  About 2 volts for green.  Revise the question:  How
>about 3 alkaline cells and 2 LEDs.  Should be a better match to the
>problem, at a 50% weight penalty.

Same here.  Who needs another 50% probability of battery failure???

And yes, I'm glad we seem to have the  green/red  issue resolved...
-- 
Neal Sedell