LED lights get dimmer over time?

[bob]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably dimmer
over the course of one to two years. Some are so dim they are useless as a
night light.

LEDs are supposed to last a long time. Could this be caused by overdriving
the LEDs? It's very disappointing.

Now I'm thinking of buying LED flood lights from hardware store eqivalent to
60W incandescent blub. Would they also become noticeably dimmer after a year
or two? If so, I'm not buying.

 

[Tim Williams]

LEDs operated at ratings last little longer than electrolytics -- a few
months. Extreme life is only obtained near room temperature, and, you know,
heatsinks are expensive, after all...

Tim

 

[Ecnerwal]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably dimmer
over the course of one to two years. Some are so dim they are useless as a
night light.

LEDs are supposed to last a long time. Could this be caused by overdriving
the LEDs? It's very disappointing.

Did the lights come with a guarantee of light output over time? If not,
that was a clue to lack of quality. If so, get them replaced.

Now I'm thinking of buying LED flood lights from hardware store eqivalent to
60W incandescent blub. Would they also become noticeably dimmer after a year
or two? If so, I'm not buying.

There are a lot of crappy things that are built with LEDs, poorly, and
at very poor lumens per watt, for sale to the uncritical masses that see
LED and look no further. If you avoid those, there's also some good
stuff coming on the market, and some stuff that might at least be worth
giving a sample item a try to see if it's any good yet. But you have to
be able to smell the pure crap and avoid it.

Aging is normal. How bad (or how much) is somewhat influenced by what
you buy. Inadequate cooling and/or overdriving the current will make it
worse, yes.

Two major-brand name not terribly cheap (well, one is actually somewhat
expensive) LEDs I have are guaranteed to produce at least 70% of rated
output at 5 years of age (or 50,000 hours). That would be noticeable,
but not (as I use them anyway) useless. The companies in question will
probably actually be around in 5 years, if the lights fail. Failure is
more likely to be a defective individual unit than a design flaw
affecting all units, if it does occur.

Chinese "night lights" from "company changes name every two weeks to
avoid liability for the junk they make" are a different story. Most are
crap from day one, and they certainly don't improve with age.

Likely the same with "flood lights" if they are house-brand or a name
you've never heard of, and don't have a 5 year or 50,000 hour guarantee.
House brand is better than unheard of if there is a guarantee, since the
hardware chain is likely to be around longer than a chimeric low-quality
company.

IMHO, if you are looking for a "flood light" (particularly an outdoor
one) and want LED, it's better to look at a fixture than a bulb. Both
the cooling and the throw of light are done better with a fixture that's
designed from the ground up as an LED fixture. But if you want an
outdoor fixture for sub-$100, I think all you're going to find at this
time and that price point is junk. Plenty of it, but it's junk.

One simple criteria (you may need to have a calculator handy, as it's
often not presented) is lumens per watt. If you stick to things that are
50 lumens per watt or better, you avoid a lot of the junk without having
to look too closely at it, or know much beyond "how many lumens" divided
by "how many watts"...

 

[Don Y]

Hi Bob,

I have two different sets of white LED night lights, both bought from

I think this is a significant point -----^^^^^^^^^^^^

costco. All of them worked quite well when new, but become noticeably
dimmer over the course of one to two years. Some are so dim they are
useless as a night light.

Most (higher power) incandescent replacement LED lights have
a "depreciation" rating -- how much light output falls over time.
Usually, something like 30% of 50,000 PoHrs. If you are only
running the light "at night" (i.e., to appease young children
sleeping in an otherwise dark house), that's >10 years!

LEDs are supposed to last a long time. Could this be caused by
overdriving the LEDs? It's very disappointing.

Now I'm thinking of buying LED flood lights from hardware store
eqivalent to 60W incandescent blub. Would they also become noticeably
dimmer after a year or two? If so, I'm not buying.

Depends on where you are located and the sorts of ambient temperatures
in which they will be operated. Heat is the killer, as always.
I have some 7W LED lamps that I've NOT used simply because of the
color temperature. The "lamps" are roughly the size of BR30's
but, instead of "glass", it's just a huge chunk of aluminum
(heat sink).

 

[hamilton]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably
dimmer over the course of one to two years. Some are so dim they are
useless as a night light.

LEDs are supposed to last a long time. Could this be caused by
overdriving the LEDs? It's very disappointing.

Now I'm thinking of buying LED flood lights from hardware store
eqivalent to 60W incandescent blub. Would they also become noticeably
dimmer after a year or two? If so, I'm not buying.

If you have an IR temp measurement device, check the temp of each unit.

LEDs degrade over time at higher heat, not light output.

But, light output is based on the amount of current thru the LED.

Temp can tell you indirectly the amount of heat being generated.

Let us know what you find.

 

[Martin Brown]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably
dimmer over the course of one to two years. Some are so dim they are
useless as a night light.

LEDs are supposed to last a long time. Could this be caused by
overdriving the LEDs? It's very disappointing.

Usually caused by poor thermal management. Particularly bad with lamps
that are "designed" (ie seriously compromised) to fit into existing lamp
fittings. What waste heat there is from an LED device ends up mostly as
heat. Filament bulbs can at least radiate a fair proportion of their
waste heat away in the near infrared and are much more tolerant of being
very hot than semiconductors.

Now I'm thinking of buying LED flood lights from hardware store
eqivalent to 60W incandescent blub. Would they also become noticeably
dimmer after a year or two? If so, I'm not buying.

Quite likely unless the heat sinking is done properly.

 

[Adrian Tuddenham]

[...]

... What waste heat there is from an LED device ends up mostly as
heat.

Can't argue with that!

 

[miso]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably
dimmer over the course of one to two years. Some are so dim they are
useless as a night light.

LEDs are supposed to last a long time. Could this be caused by
overdriving the LEDs? It's very disappointing.

Now I'm thinking of buying LED flood lights from hardware store
eqivalent to 60W incandescent blub. Would they also become noticeably
dimmer after a year or two? If so, I'm not buying.

The cheap ass ones I got from Fry's (two for a buck) have lasted for years.

However, I bought some "Lights of America" at Costco. They didn't make
it more than 6 months. Costco refunded my money.

For floods, the person who suggested getting a fixture with the LED
installed is probably on the right track. I think putting all the step
down and regulation into something the size of an Edison socket is
asking too much.

 

[Syd Rumpo]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably
dimmer over the course of one to two years. Some are so dim they are
useless as a night light.

<snip>

I wonder. Do these use batteries?

Just because they plug in to the mains doesn't mean they actually use
mains power.

Cynically yours,

 

[[email protected]]

I have two different sets of white LED night lights, both bought from
costco. All of them worked quite well when new, but become noticeably dimmer
over the course of one to two years. Some are so dim they are useless as a
night light.

LEDs are supposed to last a long time. Could this be caused by overdriving
the LEDs? It's very disappointing.

They are not overdriven, they just operate at the absolute maximum
constant ratings .

Thus, these LEDs run very hot, close to the maximum junction
temperatures, which for any electronics in general drops the lifetime
to one half for every 10°C of increased temperature.

"White" LEDs are actually blue LEDs with a fluorescent material that
converts some blue light to red and some yellow. Unfortunately due to
the hot temperatures and the intense blue radiation, the performance
of the material is deteriorated, causing a fast drop especially on
red/yellow radiation and hence total radiation. The blue might even be
more dominant, thus increasing the colour temperature as the device
gets older, perhaps after a few thousand hours.

In general, the light output from a LED drops at high junction
temperatures. In addition, the efficiency [lm/W] at high currents
(even momentarily at +25°C junction temperatures) also drops
significantly at high currents. Check for any reputable manufacturer,
such as Cree or Philips that specify the operational characteristics
at 1/2 or 1/3 of the maximum current and publish derating tables for
other temperatures and currents.

To build a highly efficient (up to 100 lm/W) light source that will
produce nearly the same amount of light (lumens) for years, one should
take "3 W" white LEDs (rated for 1000 mA max) and run them at 350 mA
(1 W). This significantly reduces aging, while simultaneously helps
heat management (smaller Rth(j-c)) Since the LED is now operating at a
higher efficiency, for the same amount of light output, less electric
input is required, generating less heat.

Thus:
* cheap 1 W lamps are made of "1 W" LEDs operating at 1 W
* expensive 1 W lamps might be made of "3 W" LEDs operated at 1 W

 

[[email protected]]

Now I'm thinking of buying LED flood lights from hardware store eqivalent to
60W incandescent blub. Would they also become noticeably dimmer after a year
or two? If so, I'm not buying.

An ordinary 60 W bulb will produce 700-750 lm and depending of CRI and
colour temperature needed, assuming 80-110 lm/W efficiency (possible
only well below maximum current), this would require 6-9 W input into
the LED array.

In order to produce the same light output for years, 6-9 LEDs each
claiming to be "3 W" but actually operated at 1 W would be required.

 

[[email protected]]

For LED degradation,
use of Arrhenius
is often erroneous.

Further, these devices have failure mechanisms that have nothing to do
with defect propagation in the die.

I agree with you that these phenomenons are going to be an issue after
100 000 hours at reasonable junction temperatures, but the drop in
blue/red conversion efficiency at 10 000 h might make the LED useless
in a few months.

 

[Martin Brown]

[email protected] wrote in


white LEDs depend on PHOSPHORS to create the "white" light from blue/UV
emissions of the semiconductor. that is why white LEDs appear yellow when
off,you're seeing the phosphors.

Phosphors eventually wear out.
the harder you drive them,the sooner they wear out.

The inorganic phosphors are generally pretty robust. It is cooking the
chip and the epoxy nearest the chip going brown that wrecks output. eg.

http://www.led-professional.com/tec...egradation-of-phosphor-converted-white-leds-1

Reports on accelerated ageing tests.

 

[miso]

This could have consequences in the LCD backlight market. We were all
given the impression that CCFT was bad technology and LED backlighting
is forever. Also to be considered is the "war" between plasma TV and
backlit LCD.

Thus far, anything white LED based that I bought that has failed has
been powered by the mains. I haven't had any LED flashlights fail. The
LED devices on that mains that failed did so in a binary fashion (no
freakin' light), not dim. I think we would be doing good to have the
Chinese LED light drivers last long enough to wear out the LEDs themselves.

 

[[email protected]]

Thus far, anything white LED based that I bought that has failed has
been powered by the mains. I haven't had any LED flashlights fail. The
LED devices on that mains that failed did so in a binary fashion (no
freakin' light), not dim. I think we would be doing good to have the
Chinese LED light drivers last long enough to wear out the LEDs themselves.

Did you open the failed LED lamp ?

Sounds that only a current limiting capacitor was used. This works OK
for a pure 50/60 Hz sine wave mains voltage. Any mains voltage peaks
(containing high harmonics) will pass the capacitor easily and a large
current peak will flow through the LEDs, killing it, if no additional
protection is used.

 

[miso]

Did you open the failed LED lamp ?

Sounds that only a current limiting capacitor was used. This works OK
for a pure 50/60 Hz sine wave mains voltage. Any mains voltage peaks
(containing high harmonics) will pass the capacitor easily and a large
current peak will flow through the LEDs, killing it, if no additional
protection is used.

I look like a bar bouncer. I just went in and requested a refund for the
crap they sold me, hauling in the dead product. I didn't have to get too
mean since there was a recall on the product. ;-)

There is an advantage to buying locally. You can get ugly in their face
if need be.