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usernam
Joined: 09 Mar 2004
Posts: 693
Helped: 129
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 15 Jan 2005 17:38 LED questions |
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What are the diode materials currently used for LED's of various colours?
Why does the light output of some LED's decrease significantly with use?
Thnx
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Alex_TSU
Joined: 19 Dec 2004
Posts: 19
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| 16 Jan 2005 1:02 Re: LED questions |
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| Various combinations of Ga-As-P & some other materials with wide carrier zone (1,5-2 V) are used mostly. The light emission capability of these LEDs runs down significantly with time when used in full current load mode. The special laser LEDs can lose approx. 50% & more of their prior emission with time causing different problems & faults in the equipment.
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usernam
Joined: 09 Mar 2004
Posts: 693
Helped: 129
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| 16 Jan 2005 10:43 Re: LED questions |
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The conduction band gap width in silicon is 1.1eV. So how is it that 1.5-2eV is enuf to produce visible light.
And also my other question is why do the LED's lose their emission capacity?
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EEHardware
Joined: 01 Apr 2004
Posts: 111
Helped: 1
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| 18 Jan 2005 3:43 LED questions |
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| Maybe,you can download something about this from internet or vendor's spec.
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masai_mara
Joined: 13 Aug 2004
Posts: 118
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| 18 Jan 2005 9:11 Re: LED questions |
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| usernam wrote: |
The conduction band gap width in silicon is 1.1eV. So how is it that 1.5-2eV is enuf to produce visible light.
And also my other question is why do the LED's lose their emission capacity? |
The photo emission is not only related to the band gap but also the impurities present. The impurities added to the pure sil/ge cause intermediate energy bands and unstable band gaps to be established in the lattice. and during an applied emf these higher diffuse energy bands are repeatedly occupied by elctrons and due to instability they decay back to the stable orbital causing photo emission. Bu I dont know why they loose their emission with time, theoritically they dont have to, unless they are contaminated.
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 18 Jan 2005 9:52 Re: LED questions |
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| usernam wrote: |
| Why does the light output of some LED's decrease significantly with use? |
Other guys said what materials, I am saying why they loose their ability to emit light after certain time. They eventually will lit less.
In thermodynamics have you heard of disorder phenomena , entropy in LED, state changes? That's what causes it.
Does it helps?
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usernam
Joined: 09 Mar 2004
Posts: 693
Helped: 129
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| 18 Jan 2005 10:15 Re: LED questions |
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| djalli wrote: |
Other guys said what materials, I am saying why they loose their ability to emit light after certain time. They eventually will lit less.
In thermodynamics have you heard of disorder phenomena , entropy in LED, state changes? That's what causes it.
Does it helps? |
Are you saying that maybe the material deteriorates with time?
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trigger74
Joined: 18 Jan 2005
Posts: 69
Helped: 4
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| 18 Jan 2005 10:29 LED questions |
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| I think the decrease in LED brightness is mainly caused by over current passes through it. It makes the materials aging faster......
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Engineer_Bob
Joined: 13 Jan 2005
Posts: 38
Helped: 6
Location: UK
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| 18 Jan 2005 10:53 Re: LED questions |
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I used to work for a company that used LED’s that had to have a stable intensity. The dimming effect that you get with LED’s caused problems.
The company got around this by running the LED’s for several weeks before they were used.
I know the LED’s do lose their brightness over time, and as I understand it this loss is most significant in the LED’s early life.
What I don’t know is why?
Djalli I had a look for disorder phenomena, didn’t really find anything, would you be kind enough to expand a little on your post?
Kind Regards Engineer Bob
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usernam
Joined: 09 Mar 2004
Posts: 693
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| 18 Jan 2005 13:29 Re: LED questions |
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| Engineer_Bob wrote: |
I know the LED’s do lose their brightness over time, and as I understand it this loss is most significant in the LED’s early life.
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I was under the impression that the loss in brightness occurs after a significant amount of run time (about 50,000 hours).
As to disorder phenomena all I could gather was that due to the past thermal history of a material the lattice structures undergoes some change which can effect the properties of the material.
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konqueror
Joined: 27 Nov 2004
Posts: 93
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| 19 Jan 2005 5:33 LED questions |
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as far as i know GaN is used for blue, GaPN is used for green GaAs is for infra red . Decrease in LED brightness is due to the Non radiative processes overtaking the radiative processes due to flow of current and deformation of lattice.
u can find this and much more in book by Saleh and Teech
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