This sounds like a step toward space habitats

LordOfWizards

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#2
Interesting stuff. Thanks Parson!
It is interesting to note that the modern LED light was explained by Einstein. The effect works both ways: Photons hitting a metal surface causes electrons to flow (given a path), and electrons hitting metal at the right energy level produces photons (what occurs in the LED).
From here:
In 1905, Einstein proposed an explanation of the photoelectric effect using a concept first put forward by Max Planck that light waves consist of tiny bundles or packets of energy known as photons or quanta.

Diagram of the maximum kinetic energy as a function of the frequency of light on zinc
The maximum kinetic energy
of an ejected electron is given by

where is the Planck constant and
is the frequency of the incident photon. The term
is the work function which gives the minimum energy required to remove a delocalised electron from the surface of the metal. The work function satisfies
= hf0
where
is the threshold frequency for the metal. The maximum kinetic energy of an ejected electron is then

Kinetic energy is positive, so we must have
for the photoelectric effect to occur.
 

Parson

This world is not my home
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#3
Okay, it is clear that I am not adequately science prepared for all of those equations, but I'm glad to have heard of them.
 

Daysman

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#4
And that's one of Einstein's earliest papers...

Of course, with an LED we're talking about a semiconductor junction, but my undergrad physics is a little faded after 30+ years, so I can't begin to discuss this with any rigor.

Do you have a decent diagram of the blue light transition, @LordOfWizards ?

I can probably handle a diagram...

(the article mentions blue light as the new thing they're playing with)
 
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LordOfWizards

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#5
Hello Daysman, Welcome to the forum. I had to go back into the article to see what you were referring to. The quote I assume is most relevant is
For decades, scientists have known that photosynthesis is optimized within the red band, but plants also need blue lightwaves to prevent stretching and enhance leaf color.
When I searched for "blue light transition" on google, I got a bunch of stuff about how Transition Lenses (the kind that adjust to brightness) block blue light. :rolleyes:

But I suppose implied in the diagram that I posted above is the fact that different metals used in the LED "crossover" at different places along the EM spectrum given the same input current and voltage. So for example in the Wiki article on LEDs here, another quote was:
The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994 and was based on InGaN. In 1995, Alberto Barbieri at the Cardiff UniversityLaboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a "transparent contact" LED using indium tin oxide (ITO) on (AlGaInP/GaAs).
So, I apologize. I don't have a diagram like that. I am an Engineer trained in both electronics and software, but I don't really specialize in many areas of electronics - I make my living writing Apps for iPhones. ;)
 

Daysman

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#6
@LordOfWizards

Thanks for the welcome -- much appreciated.

I didn't expect actual research! Perhaps I should have done, given the detail of your initial post. I merely thought you might have some useful links to hand.

Yes, that is the quote -- maybe it's just me, but it jumped out.

As for 'blue light transition' I can only apologise -- I was just trying to visualise the band gap.

The wiki article was a little dense for me, but I did find my way from there...

By the way, did you notice Asimov, A is one of the references in the photoelectric effect article?

Regards
 

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