Hello,
We are running a study to test the light output degradation of various LED. They are essentially 5mm (T13/4) LEDs. The test condition is that they are cycled (200ms ON and 1s OFF) and their light output is measured using an integrating sphere every 100,000 cycles. We noticed that all the UV LEDs are moving up at some point in power and then they will follow a regular degradation. The increase can be 10%.
We know degradation in 5mm packaged UV LED is mainly due to yellowing of the epoxy under UV light but we don't understand this big steps in output power.
Any ideas on what might be the cause?
Thank you,
P.
Any kind of light will degrade over time as the filament thins out. Bulbs which have burned for years have usually done so by being left on. Turning a bulb off then on again hastens wear. As to using more power, do you have a deposit on the contacts of the LED which is using power by heating up?
Thank you for your answer. I am not sure I described correctly the effect we are seeing. This is not the actual consumption power that will increase but the total light output of the LED as measured in the integrating sphere. I don't know the details about the internal structure of the LED/chip/contacts. We are buying them off the shelf from UV LED suppliers.
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QUOTE (patricialc+Feb 23 2007, 01:22 AM)
Hello,
We are running a study to test the light output degradation of various LED. They are essentially 5mm (T13/4) LEDs. The test condition is that they are cycled (200ms ON and 1s OFF) and their light output is measured using an integrating sphere every 100,000 cycles. We noticed that all the UV LEDs are moving up at some point in power and then they will follow a regular degradation. The increase can be 10%.
We know degradation in 5mm packaged UV LED is mainly due to yellowing of the epoxy under UV light but we don't understand this big steps in output power.
Any ideas on what might be the cause?
Thank you,
P.
The quality of any diode is degraded by all the applicable variables including normal diffusion over time. How can you keep a good quality electron hole junction interface and think it will last forever? Keeping it cool will help but it is still subject to entropy, as is everthing else. The diode interface may get better, then worse than it was as it was fabricated, but it will ultimately degrade. [QUOTE] Wbw
We are running a study to test the light output degradation of various LED. They are essentially 5mm (T13/4) LEDs. The test condition is that they are cycled (200ms ON and 1s OFF) and their light output is measured using an integrating sphere every 100,000 cycles. We noticed that all the UV LEDs are moving up at some point in power and then they will follow a regular degradation. The increase can be 10%.
We know degradation in 5mm packaged UV LED is mainly due to yellowing of the epoxy under UV light but we don't understand this big steps in output power.
Any ideas on what might be the cause?
Thank you,
P.
The quality of any diode is degraded by all the applicable variables including normal diffusion over time. How can you keep a good quality electron hole junction interface and think it will last forever? Keeping it cool will help but it is still subject to entropy, as is everthing else. The diode interface may get better, then worse than it was as it was fabricated, but it will ultimately degrade. [QUOTE] Wbw
Dropped an eye: The technology of UV Led is just horrible. Examples, though I ignore if today's fabrications resembles yesterday's research:
http://www.wat.edu.pl/review/optor/10(4)287.pdf
http://www.mrs.org/s_mrs/bin.asp?CID=2561&...48&DOC=FILE.PDF
So basically this is full of unhealthy technological processes, and as any light emitter, Leds must be operated at tremendous current densities - lasers are even worse. Nothing surprising that they drift in time; A temporary improvement is less expected but possible.
I doubt cycling shortens the life of a UV Led; It is said to have little effect on a visible Led. Did you try? You can shorten your experiment by a factor of 6 if it doesn't have any effect.
Temperature on the other hand must have a brutal effect, so cycling may in fact ease the life of your Leds. And "on" current is probably the first or second factor in life expectancy.
http://www.wat.edu.pl/review/optor/10(4)287.pdf
http://www.mrs.org/s_mrs/bin.asp?CID=2561&...48&DOC=FILE.PDF
So basically this is full of unhealthy technological processes, and as any light emitter, Leds must be operated at tremendous current densities - lasers are even worse. Nothing surprising that they drift in time; A temporary improvement is less expected but possible.
I doubt cycling shortens the life of a UV Led; It is said to have little effect on a visible Led. Did you try? You can shorten your experiment by a factor of 6 if it doesn't have any effect.
Temperature on the other hand must have a brutal effect, so cycling may in fact ease the life of your Leds. And "on" current is probably the first or second factor in life expectancy.
QUOTE (Enthalpy+Jul 3 2007, 12:39 AM)
Dropped an eye: The technology of UV Led is just horrible. Examples, though I ignore if today's fabrications resembles yesterday's research:
http://www.wat.edu.pl/review/optor/10(4)287.pdf
http://www.mrs.org/s_mrs/bin.asp?CID=2561&...48&DOC=FILE.PDF
So basically this is full of unhealthy technological processes, and as any light emitter, Leds must be operated at tremendous current densities - lasers are even worse. Nothing surprising that they drift in time; A temporary improvement is less expected but possible.
I doubt cycling shortens the life of a UV Led; It is said to have little effect on a visible Led. Did you try? You can shorten your experiment by a factor of 6 if it doesn't have any effect.
Temperature on the other hand must have a brutal effect, so cycling may in fact ease the life of your Leds. And "on" current is probably the first or second factor in life expectancy.
ENTHALPY:
Concur with your comment. I note also that back biasing to prebreakdown leads to even more interesting results, including the Josephson junction UHF effect. I don't know whether that was improved enough to get into the UHF range that it had, without its destruction. I was discouraged that as soon as "we" found any new devices it was given the "outsource treatment", so I left that field and worked in the reverse. Maimon and the maser, and BUbe and Lax with the laser, are examples, but nothing to match that of the 1992 plus donations. WBW
http://www.wat.edu.pl/review/optor/10(4)287.pdf
http://www.mrs.org/s_mrs/bin.asp?CID=2561&...48&DOC=FILE.PDF
So basically this is full of unhealthy technological processes, and as any light emitter, Leds must be operated at tremendous current densities - lasers are even worse. Nothing surprising that they drift in time; A temporary improvement is less expected but possible.
I doubt cycling shortens the life of a UV Led; It is said to have little effect on a visible Led. Did you try? You can shorten your experiment by a factor of 6 if it doesn't have any effect.
Temperature on the other hand must have a brutal effect, so cycling may in fact ease the life of your Leds. And "on" current is probably the first or second factor in life expectancy.
ENTHALPY:
Concur with your comment. I note also that back biasing to prebreakdown leads to even more interesting results, including the Josephson junction UHF effect. I don't know whether that was improved enough to get into the UHF range that it had, without its destruction. I was discouraged that as soon as "we" found any new devices it was given the "outsource treatment", so I left that field and worked in the reverse. Maimon and the maser, and BUbe and Lax with the laser, are examples, but nothing to match that of the 1992 plus donations. WBW
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