Date: Fri Mar 12 11:38:48 2010

Author: Dale E. Stille

Subject: Re: LED with LN2



I can go both ways.....color wise that is. I have some oranges that go
to yellow, and some greens that go to yellow. Both are Radio Shack, but
you can't get the orange anymore. However, I believe that these will
work although I haven't tested them yet,
or these maybe

The greens are # 276-304 Radio Shack. As the cooling greatly increases
the current flow to these (enough to crack the case on a couple due to
thermal), I also put a 100 ohm resistor in series.


Adam Beehler wrote:
> That explains it, Dale. At least now I know I was not missing
> something. Thank you. By the way, do your LEDs shift to shorter
> wavelengths when cooled? What LEDs do you use?
> Adam Beehler
> Dale E. Stille wrote:
>> Adam,
>> You need to look closer. My 7A30.10 entry is actually in the Millikan
>> Oil Drop section but is just there for the order. If there was a
>> section in the BIB for this, it would fall between the Millikan Oil
>> drop section and the Compton Effect Section or somewhere between the
>> Compton Section and the Wave Mechanics section. However, since there
>> has been no specific publication on this demo, there is no "official"
>> PIRA BIB number.
>> As to the principle being "photoelectric effect" that is just a
>> carryover from the page we constructed this entry from. Basically,
>> until there is an official explanation for this, I don't know where
>> the hell it goes.........
>> All in the bookkeeping,
>> Dale
>> Adam Beehler wrote:
>>> David Maiullo wrote:
>>>> On another note, who does the LED in LN2 demo? Anyone know what its
>>>> PIRA number is? Does it have one? What's everyone's favorite
>>>> explanation for the effect of the color change? Changing the band
>>>> gap? In what way?
>>> I created a setup for this demonstration as well; however, it has not
>>> been done in a classroom as of yet. I am the only one that has ever
>>> done or shown it. Oh well. That is sort of all right since there
>>> seems to be no definitive explanation for the results. Jerry Zani
>>> explained to me, as mentioned by him again in this thread, that the
>>> effect is to have the color of the LED shift inversely with the
>>> temperature change; thus, decreasing the temperature should make the
>>> LED's color shift towards shorter wavelengths (higher frequencies).
>>> My experience is that all of the LEDs I have tried have shifted the
>>> "wrong" way, if they shift at all. I can indeed get most to shift,
>>> but again, the "wrong" way. If Zani's explanation is correct, then I
>>> should not be showing this demo because I am getting the wrong
>>> results. Jerry, do you have a specific type of LED you use? I went
>>> to Radio Shack and bought about 20 different styles and colors of
>>> LEDs and had no luck. How do we know what makes a certain type of
>>> LED work the "right" way. Of course, if we knew this then maybe we
>>> would understand better the real phenomenon at work here. Alas,
>>> where is our scientific journal article that explains this effect
>>> specifically? Arg! Ok, so if the LED is "suppose" to shift to
>>> shorter wavelengths and we are not certain why, then do we know why
>>> some LEDs shift the other way?
>>> On another note, two people have mentioned that they give this
>>> demonstration the PIRA DSC number of 7A30.10. What am I missing? I
>>> see no such section in the bibliography (i.e. 7A30). Dale's web page
>>> says that the principle is the "photoelectric effect." Is that just
>>> a typo, Dale?