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How LEDs Work Answered

Right, so i know that LEDs work when a electron meets a hole and drops into a lower energy state. This releases energy in the form of a photon.
After a few experiments for college i can show that as current increases light output increases i'm assuming this is because more current = more electrons = more energy released = more photons = more light output. Correct?

Another of the experiments i did was to investigate the heat around the led and the light out. It turns out that as the heat goes up, lumen output goes down.
Now the question, why (in a physical sense) does this happen?
Do the holes become less? why?

Thanks ppl

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drummer ian
drummer ian

13 years ago

any ideas? i am also confused why the efficiency curves off at around 300mA, is this because there are too many electrons or something?

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Lftndbt
Lftndbt

13 years ago

Hmmm...
Steve has just confused me lil'...
The way phrased your post is also slightly confusing me....
You clearly say you have investigated that "it turns out that as the heat goes up, lumen output goes down."
Like steve said there are several variables, that may be missing here. Your post unfortunatley does not expand enough for me to give a confident answer....
Heat goes up? As in length of operation time, increasing heat vs time functioning....
Or as in instantanious operation, of variable voltage to the LeD and to what extent?
Yes there is definatley a point where if you overload a LeD, the heat will continue to rise without Lumen responce but at the Led's max level?
I will assume that you are referring to a constant at a variable range. If you are then that would be very interesting, because I was not under that impression...

Please elaborate if you don't mind...
Cheers....

Nice post....

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drummer ian
drummer ian

Reply 13 years ago

Sorry, had to be a quick post and i can't have explained very well, the way i set the experiment up was to have a hair dryer to heat the surrounding air of the LED, i measured this with 2 temperature probes. I used a lux meter to measure the LEDs output at different temperatures and was wondering if there is a scientific explanation as to why the results were that lumens drop when the LED is in a higher heated environment?

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Lftndbt
Lftndbt

Reply 13 years ago

Ok, that makes alot more sense.... We still need to know if it was a constant decline or not... But i'll assume it is... Buggered if I know.... Unless your talking extreme heats I can't see why there would be a gradually decrease in lumens vs heat increase... It's sounds like your talking extreme's.... What was the overall lux decrease vs lumen... I can't imagine there would be a significant difference in lumen output.... Do you still have any results on hand?

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drummer ian
drummer ian

Reply 13 years ago

i have the results, they were only across a small range of heats like 40 degrees c to about room temp, there was a deffinate decline in lumens though as the led got hotter. i'm just wondering why this is? surely the electrons have more energy when hot = more light !?

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steven07
steven07

Reply 13 years ago

Oh i think was going along the wrong track . I was thinking that he when he set the led to a lower voltage more heat was observed than when he set it to a higher voltage because comparitivly more lower wavelength light may be produced since the only lower transition's are possible at lower energy's, depending on the emission spetra of the target.

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Lftndbt
Lftndbt

Reply 13 years ago

Am I going nuts or did steven07 post dissapear... or is it just damn net stuffing.. up?? That was weird

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steven07
steven07

Reply 13 years ago

i deleted it because i wasn't answering the question

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steven07
steven07

13 years ago

I have a quick practical explanation. you know how when you heat up a conductor the resistance increases? you heat up the LED and the led's resistance increases. there , did i solve it ? or have i overlooked something