LEDs life time?

A

Aleksandar Stancic

Guest
Hi everybody!

I'm using a LITE-ON LED diode LTL307EE.

Tha datasheet says:
Absolute maximum ratings at Ta=25C:
Continuous Forward Current = 30mA

Does that mean that the LED will not lose it's brightness
even after years and years of work (at 25C)?

Thank you!
 
On Tue, 31 Aug 2004 19:27:24 +0200, the renowned "Aleksandar Stancic"
<astancic@EUnet.yu> wrote:

Hi everybody!

I'm using a LITE-ON LED diode LTL307EE.

Tha datasheet says:
Absolute maximum ratings at Ta=25C:
Continuous Forward Current = 30mA

Does that mean that the LED will not lose it's brightness
even after years and years of work (at 25C)?
Click to expand...
No, it means that they don't guarantee it will last a second at 31mA
and 25°C ambient. It says nothing about the life at the abs. max.
current, but one may guess it will be a fair bit less than it would be
at, say, 10mA and 20°C.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
In article <ch2cuf$ac4$1@news.beotel.net>, Aleksandar Stancic wrote:
Hi everybody!

I'm using a LITE-ON LED diode LTL307EE.

Tha datasheet says:
Absolute maximum ratings at Ta=25C:
Continuous Forward Current = 30mA

Does that mean that the LED will not lose it's brightness
even after years and years of work (at 25C)?
Click to expand...
Look up thermal resistance data for your LED or a similar one.

Many LEDs have thermal resistance of approx. 250 degrees C per watt, in
terms of temperature rise of the junction above the temperature 5 mm
outside the case on the lead that the chip is mounted on.

For really good life expectancy (at least half the original light output
after 100,000 operating hours) I advise having the junction not exceed 85
degrees C (some may tolerate a little more like 100 degrees C), maybe also
do not exceed 20 mA or not by much.
Keep in mind that violet and UV LEDs have shorter life expectancy, and
ones with phosphors (white, pink, purple, and Nichia's yellow) also have
shorter life expectancy at "full power".

- Don Klipstein (don@misty.com)
 
On Tue, 31 Aug 2004 19:27:24 +0200 "Aleksandar Stancic"
<astancic@EUnet.yu> wrote:

Hi everybody!

I'm using a LITE-ON LED diode LTL307EE.

Tha datasheet says:
Absolute maximum ratings at Ta=25C:
Continuous Forward Current = 30mA

Does that mean that the LED will not lose it's brightness
even after years and years of work (at 25C)?
Click to expand...
No, that just means that you should be able to put this much current
thru it without its dying rather quickly.

In general, LEDs which are run continuously at their max current
rating lose about half of their light output in one year of operation.
I assume that the rate of loss is much less if they are worked well
below their max.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------
 
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote in
message news:10jtkptd5k9red3@corp.supernews.com...
"Aleksandar Stancic" <astancic@EUnet.yu> wrote in message
news:chl1bg$qia$1@news.beotel.net...
Hi everybody!

I'm using a LITE-ON LED diode LTL307EE.

Tha datasheet says:
Absolute maximum ratings at Ta=25C:
Continuous Forward Current = 30mA

Does that mean that the LED will not lose it's brightness
even after years and years of work (at 25C)?

Thank you!

OT Snipped

I've been running some cheap Hong Kong white LEDs at 25 and 20 mA.
After two months or about 1500 hrs at 25mA, the first two dimmed to
where they were barely visible. The second two, running at 20 mA, have
already dimmed after about the same time, but not dimmed as badly.
Since this is just an eyeball guesstimation, I can't give any accurate
measurement. But it's sufficient to say that running these LEDs at near
their rated maximum will cause them to dim much sooner than the usual
"100 thousand hours" lifetime that everyone seems to use for white LEDs.

Along with these two, I've had another pair of good quality Nichia white
LEDs, and they are still going strong. I imagine they've dimmed
somewhat, but I can't tell with my eyeballs. The same pair has been in
series with the first and second two cheapo LEDs the whole four months
or about 3000 hours. The room temp this summer has been unusually mild,
between 72 to 82 deg F.
Click to expand...
Take some readings of the actual light emitted, so the test can mean something
besides THEY GET DIMMER.

Your do have a meter calibrated in Lumens or MCP, don't you?
 
"Clarence" <No@No.Com> wrote in message
news:hSH%c.17567$ou5.8493@newssvr29.news.prodigy.com...
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com
wrote in
message news:10jtkptd5k9red3@corp.supernews.com...

"Aleksandar Stancic" <astancic@EUnet.yu> wrote in message
news:chl1bg$qia$1@news.beotel.net...
Hi everybody!

I'm using a LITE-ON LED diode LTL307EE.

Tha datasheet says:
Absolute maximum ratings at Ta=25C:
Continuous Forward Current = 30mA

Does that mean that the LED will not lose it's brightness
even after years and years of work (at 25C)?

Thank you!

OT Snipped

I've been running some cheap Hong Kong white LEDs at 25 and 20 mA.
After two months or about 1500 hrs at 25mA, the first two dimmed to
where they were barely visible. The second two, running at 20 mA,
have
already dimmed after about the same time, but not dimmed as badly.
Since this is just an eyeball guesstimation, I can't give any
accurate
measurement. But it's sufficient to say that running these LEDs at
near
their rated maximum will cause them to dim much sooner than the
usual
"100 thousand hours" lifetime that everyone seems to use for white
LEDs.

Along with these two, I've had another pair of good quality Nichia
white
LEDs, and they are still going strong. I imagine they've dimmed
somewhat, but I can't tell with my eyeballs. The same pair has been
in
series with the first and second two cheapo LEDs the whole four
months
or about 3000 hours. The room temp this summer has been unusually
mild,
between 72 to 82 deg F.

Take some readings of the actual light emitted, so the test can mean
something
besides THEY GET DIMMER.

Your do have a meter calibrated in Lumens or MCP, don't you?
Click to expand...
No, I don't have one and I don't need one. You were told that it was a
subjective test. If you don't like the resuts, don't read them and go
do your own tests.

The facts are obvious. If you buy cheap LEDs, you get what you pay for.
 
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