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changing wavelength of led

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greenfarm

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hello all this is my first post. i want to know is there a way to change the wavelength of an led with in the range of the led by ajesting the voltage, temp or something like that. thanks
 

keith1200rs

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Not really. I think wavelength does change slightly with temperature and drive current but not enough to be useful.

Keith
 

greenfarm

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thanks. what im trying to do is take an led that 450 nm and has a range of 440 to 460 nm and make is so the peak is 440 nm. i have not found a led that has a peak of 440 nm if you find one like that it will solve my problem. also i am willing to go as far as to use liquid N2 to change the wavelength. thanks
 

keith1200rs

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Normally for that sort of problem I would find an LED with significant output at 440, even if it is not the peak, and use an interference filter at 440,

Keith

Added after 31 minutes:

By the way, there are LEDs around that peak at 440nm such as from ETG. See etgtech.com

Or coolled.com

Keith
 

greenfarm

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wow thanks. they are the wavelength im looking for, but look really expensive. i just found an led that might work but im not sure if i should believe them that it dose what they say it dose. here take a look http://www.superbrightleds.com/cgi-...ion=DispPage&Page2Disp=/specs/v1015_specs.htm
tell me what you think. i dont need the led to be olny 440 nm you see im using them to grow a plant. chlorophyll A has a max absotion at 440 nm and 660 nm i need a ton of leds so they need to be cheap the ones in the link are kinda still to exspensive. if anyone finds what im looking for and is cheap this would really help thanks.
 

flatulent

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The wavelength is mostly controlled by the doping impurities used to make the semiconducting material.

You can improve your system link in other ways such as using lenses or parabolic reflectors if your link is just one point to another point type.
 

keith1200rs

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If you are just using it to make a plant grow, won't a light bulb do? Do you really need to exclude all other wavelengths? If you do, for some research reason, it may be cheaper to simply use a light bulb and narrowband interference filter. Specialist LEDs can be quite expensive. They are often only made in low volumes for clinical fluoroscopy.

Keith.
 

FvM

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I know, that LED's are often used as cheap spectroscopic sources. Blue LEDs have a typical half power bandwidth of about 60 nm.
Furthermore most (GaN type) have an optical peak wavelength of 430 (or more exactly 428) nm. They are often advertised as 465 nm,
which is the visual centre wavelength due to eye characteristic. They have about 90% of it's peak intensity at 440 nm. But the TC is
only 0.004 nm/K, so there's no chance to mave the peak to 440 nm exactly.
 

jgruszynski

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Not without changing the reliability of the device. For fun we once dunked an LED in LN2 and pumped nearly 10A into it - its bands certainly got bent and its wavelength changed but it didn't survive more than a few minutes even in LN2.

For most LEDs there are two ways wavelength is controlled. The old-school way is by the semiconductor chosen (it's the band gap) which obviously can't be changed once made.

The new-school way is to build a violet or ultraviolent LED and use fluorescent materials either atop the LED die or in the plastic package. This is how most white LEDs are done - strictly it's the same way that fluorescent lights work, just without the mercury UV lamp. Old tricks are often the best tricks.

In the cases where you may have seen LEDs that change color, this is done by back-wiring a pair of LEDs (e.g. red and green) such that flow in one direction turns on the red and in the opposite direction turns on the green. Some games can be played with asymmetric duty cycle pulse biasing to get colors in between red and green. I seem to remember the same trick with an additional blue LED and terminal for RGB but I haven't really looked into those.
 

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