Aging LEDs - does their output drop after turn-on?LED circuit with 17 parallel diodesUse of LED driven over-current in a strobe lampconnect LEDs to USB keyboard – but they turn off after a secondUniformly illuminate an array of LEDs: how to get the most homogeneous output?Will connecting two batteries in parallel increase current drawn in simple led circuit?Why are 'modern' high-efficiency LEDs easier to damage than 'old' LEDs?Temperature conpensated LED DriveCurrent Source Output Does Not Become 0LED Intensity variation with Temperature (At constant Forward Current)?Why a damaged LED was acting like a weird memory cell?
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Aging LEDs - does their output drop after turn-on?
LED circuit with 17 parallel diodesUse of LED driven over-current in a strobe lampconnect LEDs to USB keyboard – but they turn off after a secondUniformly illuminate an array of LEDs: how to get the most homogeneous output?Will connecting two batteries in parallel increase current drawn in simple led circuit?Why are 'modern' high-efficiency LEDs easier to damage than 'old' LEDs?Temperature conpensated LED DriveCurrent Source Output Does Not Become 0LED Intensity variation with Temperature (At constant Forward Current)?Why a damaged LED was acting like a weird memory cell?
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$begingroup$
Old LEDs tend to have a lower optical ouput than new ones for the same current.
However, are there any other things associated with an old LED? Specifically, does the output remain constant with constant current at constant external temperature over small time intervals eg hours?
led
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
$endgroup$
add a comment |
$begingroup$
Old LEDs tend to have a lower optical ouput than new ones for the same current.
However, are there any other things associated with an old LED? Specifically, does the output remain constant with constant current at constant external temperature over small time intervals eg hours?
led
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
$endgroup$
1
$begingroup$
good question +1
$endgroup$
– Neil_UK
9 hours ago
$begingroup$
Yes it does. What makes you think otherwise???
$endgroup$
– Kripacharya
9 hours ago
$begingroup$
Do you mean old LEDs of the same design as new ones?
$endgroup$
– HandyHowie
9 hours ago
$begingroup$
@HandyHowie Yes - same design, old v new
$endgroup$
– Dirk Bruere
9 hours ago
add a comment |
$begingroup$
Old LEDs tend to have a lower optical ouput than new ones for the same current.
However, are there any other things associated with an old LED? Specifically, does the output remain constant with constant current at constant external temperature over small time intervals eg hours?
led
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
$endgroup$
Old LEDs tend to have a lower optical ouput than new ones for the same current.
However, are there any other things associated with an old LED? Specifically, does the output remain constant with constant current at constant external temperature over small time intervals eg hours?
led
led
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
asked 9 hours ago
Dirk BruereDirk Bruere
6,4475 gold badges33 silver badges71 bronze badges
6,4475 gold badges33 silver badges71 bronze badges
1
$begingroup$
good question +1
$endgroup$
– Neil_UK
9 hours ago
$begingroup$
Yes it does. What makes you think otherwise???
$endgroup$
– Kripacharya
9 hours ago
$begingroup$
Do you mean old LEDs of the same design as new ones?
$endgroup$
– HandyHowie
9 hours ago
$begingroup$
@HandyHowie Yes - same design, old v new
$endgroup$
– Dirk Bruere
9 hours ago
add a comment |
1
$begingroup$
good question +1
$endgroup$
– Neil_UK
9 hours ago
$begingroup$
Yes it does. What makes you think otherwise???
$endgroup$
– Kripacharya
9 hours ago
$begingroup$
Do you mean old LEDs of the same design as new ones?
$endgroup$
– HandyHowie
9 hours ago
$begingroup$
@HandyHowie Yes - same design, old v new
$endgroup$
– Dirk Bruere
9 hours ago
1
1
$begingroup$
good question +1
$endgroup$
– Neil_UK
9 hours ago
$begingroup$
good question +1
$endgroup$
– Neil_UK
9 hours ago
$begingroup$
Yes it does. What makes you think otherwise???
$endgroup$
– Kripacharya
9 hours ago
$begingroup$
Yes it does. What makes you think otherwise???
$endgroup$
– Kripacharya
9 hours ago
$begingroup$
Do you mean old LEDs of the same design as new ones?
$endgroup$
– HandyHowie
9 hours ago
$begingroup$
Do you mean old LEDs of the same design as new ones?
$endgroup$
– HandyHowie
9 hours ago
$begingroup$
@HandyHowie Yes - same design, old v new
$endgroup$
– Dirk Bruere
9 hours ago
$begingroup$
@HandyHowie Yes - same design, old v new
$endgroup$
– Dirk Bruere
9 hours ago
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
There are a lot of papers on LED aging (some on optocoupler aging, where the LED is by far the dominant factor), and it seems to be significant for IR to UV wavelengths, and accelerated by temperature. There are also papers on the optical "noise" from LEDs. The above-linked paper shows a very nice graph of 1/f noise down to 1Hz BW, extrapolation is risky though.
I believe that variations in Vf with time would tend to imply that constant current will yield a more stable optical output.
Last I looked in detail at this, many of the papers were looking at ways to reduce the aging effects so it's reasonable to conclude that they've probably been getting better, at least from reputable manufacturers. I believe there can be a large difference in LED aging between manufacturers, based on the optocoupler aging information I looked at some years ago, with the top-tier Japanese sources well ahead at the time.
The venerable IL300 analog optical isolator uses two LED dice with feedback from a photodiode in order to stabilize the output of the two LEDs, with the implicit assumption that the light output of two similar LEDs operated at essentially the same forward current and under the same ambient temperature conditions will exhibit similar changes with regard to temperature changes and aging.
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
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1 Answer
1
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1 Answer
1
active
oldest
votes
active
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active
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votes
$begingroup$
There are a lot of papers on LED aging (some on optocoupler aging, where the LED is by far the dominant factor), and it seems to be significant for IR to UV wavelengths, and accelerated by temperature. There are also papers on the optical "noise" from LEDs. The above-linked paper shows a very nice graph of 1/f noise down to 1Hz BW, extrapolation is risky though.
I believe that variations in Vf with time would tend to imply that constant current will yield a more stable optical output.
Last I looked in detail at this, many of the papers were looking at ways to reduce the aging effects so it's reasonable to conclude that they've probably been getting better, at least from reputable manufacturers. I believe there can be a large difference in LED aging between manufacturers, based on the optocoupler aging information I looked at some years ago, with the top-tier Japanese sources well ahead at the time.
The venerable IL300 analog optical isolator uses two LED dice with feedback from a photodiode in order to stabilize the output of the two LEDs, with the implicit assumption that the light output of two similar LEDs operated at essentially the same forward current and under the same ambient temperature conditions will exhibit similar changes with regard to temperature changes and aging.
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
$endgroup$
add a comment |
$begingroup$
There are a lot of papers on LED aging (some on optocoupler aging, where the LED is by far the dominant factor), and it seems to be significant for IR to UV wavelengths, and accelerated by temperature. There are also papers on the optical "noise" from LEDs. The above-linked paper shows a very nice graph of 1/f noise down to 1Hz BW, extrapolation is risky though.
I believe that variations in Vf with time would tend to imply that constant current will yield a more stable optical output.
Last I looked in detail at this, many of the papers were looking at ways to reduce the aging effects so it's reasonable to conclude that they've probably been getting better, at least from reputable manufacturers. I believe there can be a large difference in LED aging between manufacturers, based on the optocoupler aging information I looked at some years ago, with the top-tier Japanese sources well ahead at the time.
The venerable IL300 analog optical isolator uses two LED dice with feedback from a photodiode in order to stabilize the output of the two LEDs, with the implicit assumption that the light output of two similar LEDs operated at essentially the same forward current and under the same ambient temperature conditions will exhibit similar changes with regard to temperature changes and aging.
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
$endgroup$
add a comment |
$begingroup$
There are a lot of papers on LED aging (some on optocoupler aging, where the LED is by far the dominant factor), and it seems to be significant for IR to UV wavelengths, and accelerated by temperature. There are also papers on the optical "noise" from LEDs. The above-linked paper shows a very nice graph of 1/f noise down to 1Hz BW, extrapolation is risky though.
I believe that variations in Vf with time would tend to imply that constant current will yield a more stable optical output.
Last I looked in detail at this, many of the papers were looking at ways to reduce the aging effects so it's reasonable to conclude that they've probably been getting better, at least from reputable manufacturers. I believe there can be a large difference in LED aging between manufacturers, based on the optocoupler aging information I looked at some years ago, with the top-tier Japanese sources well ahead at the time.
The venerable IL300 analog optical isolator uses two LED dice with feedback from a photodiode in order to stabilize the output of the two LEDs, with the implicit assumption that the light output of two similar LEDs operated at essentially the same forward current and under the same ambient temperature conditions will exhibit similar changes with regard to temperature changes and aging.
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
$endgroup$
There are a lot of papers on LED aging (some on optocoupler aging, where the LED is by far the dominant factor), and it seems to be significant for IR to UV wavelengths, and accelerated by temperature. There are also papers on the optical "noise" from LEDs. The above-linked paper shows a very nice graph of 1/f noise down to 1Hz BW, extrapolation is risky though.
I believe that variations in Vf with time would tend to imply that constant current will yield a more stable optical output.
Last I looked in detail at this, many of the papers were looking at ways to reduce the aging effects so it's reasonable to conclude that they've probably been getting better, at least from reputable manufacturers. I believe there can be a large difference in LED aging between manufacturers, based on the optocoupler aging information I looked at some years ago, with the top-tier Japanese sources well ahead at the time.
The venerable IL300 analog optical isolator uses two LED dice with feedback from a photodiode in order to stabilize the output of the two LEDs, with the implicit assumption that the light output of two similar LEDs operated at essentially the same forward current and under the same ambient temperature conditions will exhibit similar changes with regard to temperature changes and aging.
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
edited 8 hours ago
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
answered 9 hours ago
Spehro PefhanySpehro Pefhany
219k5 gold badges175 silver badges455 bronze badges
219k5 gold badges175 silver badges455 bronze badges
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1
$begingroup$
good question +1
$endgroup$
– Neil_UK
9 hours ago
$begingroup$
Yes it does. What makes you think otherwise???
$endgroup$
– Kripacharya
9 hours ago
$begingroup$
Do you mean old LEDs of the same design as new ones?
$endgroup$
– HandyHowie
9 hours ago
$begingroup$
@HandyHowie Yes - same design, old v new
$endgroup$
– Dirk Bruere
9 hours ago