LED 'lifetime'?
Pete
I'm curious about the "Important" warning message I found on a wind-up
LED torch (flashlight) I just got for Christmas. It says:
"IMPORTANT: To extend the life of the LEDs allow 20 seconds between
turning ON & OFF. Do not turn ON & OFF repeatedly."
Hunh...? I can't imagine what effect that would have on LEDs. There's
no turn-on surge like an incandescent would have. How could the life
be shortened?
I searched the web for that message, and find a number of apparently
quite different and independent products with the same warning -- all,
interestingly from UK suppliers! (Though my unit is made in China.)
Could this be some kind of weirdly spreading myth?
-- Pete --
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Zootal
"Pete" <neve...@GOODEVEca.net> wrote in message
news:duCdnQ7zT7I9A6TW...@lmi.net...
>
> I'm curious about the "Important" warning message I found on a wind-up
> LED torch (flashlight) I just got for Christmas. It says:
>
> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
> turning ON & OFF. Do not turn ON & OFF repeatedly."
>
> Hunh...? I can't imagine what effect that would have on LEDs. There's
> no turn-on surge like an incandescent would have. How could the life
> be shortened?
>
> I searched the web for that message, and find a number of apparently
> quite different and independent products with the same warning -- all,
> interestingly from UK suppliers! (Though my unit is made in China.)
> Could this be some kind of weirdly spreading myth?
>
> -- Pete --
>
If the LEDs are driven hard enough, then cycling them on and off could cause
thermal stress which shortens the life of the LED. That is a pretty piss
poor design, but welcome to the world of plastic made in China piece of cr*p
mass merchandizing (eg Wal-Mart, etc.). I would not expect a good quality
LED flashlight to have this limitation. It's also entirely possible that the
message is just a canned message that doesn't necessarily apply.
I have a windup LED flashlight, but it doesn't have that warning on it. That
doesn't mean it won't burn out the LEDs, it might be that they didn't know
this a few years ago when I bought it. It says "Megabrite" on the top, but
doesn't state country of origin. It works OK, but the battery it comes with
is so small to be almost worthless. When I get a roundtuit, I'm going to
replace it with a couple of regular AA NiMH batteries in a holder so the
batteries can be removed and charged.
I've seen lasers that had a life rated in the number of power cycles, not
how many hours it operated. If you turned it on and left it on, it would run
for a million years. If you power cycle it every five minutes, it would be
dead in a week.
Jasen Betts
>
> I'm curious about the "Important" warning message I found on a wind-up
> LED torch (flashlight) I just got for Christmas. It says:
>
> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
> turning ON & OFF. Do not turn ON & OFF repeatedly."
>
> Hunh...? I can't imagine what effect that would have on LEDs. There's
> no turn-on surge like an incandescent would have. How could the life
> be shortened?
internal resistance and surface charge effect from the supercap?
switcher that comes on with a surge?
--- news://freenews.netfront.net/ - complaints: ne...@netfront.net ---
John Fields
wrote:
>
>I'm curious about the "Important" warning message I found on a wind-up
>LED torch (flashlight) I just got for Christmas. It says:
>
> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
> turning ON & OFF. Do not turn ON & OFF repeatedly."
>
>Hunh...? I can't imagine what effect that would have on LEDs. There's
>no turn-on surge like an incandescent would have. How could the life
>be shortened?
---
Since they want you to wait 20 seconds between turn-on and turn-off,
there will, ostensibly, be no turn-on surge from the supply and, since
LED's don't exhibit the same VI characteristics as incandescents, no
turn-on current spike through the LED.
What they're talking about is a _turn-off_ surge, so I suspect that 20
second wait will allow the thing to do whatever it needs to in order to
do a soft turn-off.
---
>I searched the web for that message, and find a number of apparently
>quite different and independent products with the same warning -- all,
>interestingly from UK suppliers! (Though my unit is made in China.)
>Could this be some kind of weirdly spreading myth?
---
I doubt it.
More than likely it's that the same (cheap) design has found its way
into many related products.
JF
Pete
Zootal <use...@spam.zootal.nospam.com> wrote:
>
>"Pete" <neve...@GOODEVEca.net> wrote in message
>news:duCdnQ7zT7I9A6TW...@lmi.net...
>>
>> I'm curious about the "Important" warning message I found on a wind-up
>> LED torch (flashlight) I just got for Christmas. It says:
>>
>> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
>> turning ON & OFF. Do not turn ON & OFF repeatedly."
>>
>> Hunh...? I can't imagine what effect that would have on LEDs. There's
>> no turn-on surge like an incandescent would have. How could the life
>> be shortened?
>
>thermal stress which shortens the life of the LED.
if you gave it time to heat up.
> [.......] I would not expect a good quality
Pete
Jasen Betts <ja...@xnet.co.nz> wrote:
>On 2009-12-29, Pete <neve...@GOODEVEca.net> wrote:
>>
>> I'm curious about the "Important" warning message I found on a wind-up
>> LED torch (flashlight) I just got for Christmas. It says:
>>
>> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
>> turning ON & OFF. Do not turn ON & OFF repeatedly."
>>
Possible, I suppose. I'd have thought they'd say "battery", but maybe
they thought that was too complicated... (:-/)
>
>switcher that comes on with a surge?
Pete
John Fields <jfi...@austininstruments.com> wrote:
>>
>> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
>> turning ON & OFF. Do not turn ON & OFF repeatedly."
>
>
>second wait will allow the thing to do whatever it needs to in order to
>do a soft turn-off.
thermal shock as another poster suggested but otherwise I can't see
what a sudden current cut-off could do.
>---
>
>>Could this be some kind of weirdly spreading myth?
>
>
>More than likely it's that the same (cheap) design has found its way
>into many related products.
torch to a 'super bright" 30-LED wand. And, as I said, all advertised
by UK sales outlets. None in the US that I can find.
John Fields
wrote:
>In article <vevmj5hcoigs0iqn2...@4ax.com>,
>John Fields <jfi...@austininstruments.com> wrote:
>>>
>>> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
>>> turning ON & OFF. Do not turn ON & OFF repeatedly."
>>
>>
>>What they're talking about is a _turn-off_ surge, so I suspect that 20
>>second wait will allow the thing to do whatever it needs to in order to
>>do a soft turn-off.
>Turn *off* surge?? Where would that happen? I suppose there could be
>thermal shock as another poster suggested but otherwise I can't see
>what a sudden current cut-off could do.
---
L dI
E = ------
dt
---
>>>Could this be some kind of weirdly spreading myth?
>>
>>I doubt it.
>>
>>More than likely it's that the same (cheap) design has found its way
>>into many related products.
> Strange, though, that it covers such a range -- from my little 2-LED
>torch to a 'super bright" 30-LED wand.
---
Scaling of the same bad design, probably.
Take one apart and post what you find in it?
---
>And, as I said, all advertised
>by UK sales outlets. None in the US that I can find.
---
OK
JF
Pete
John Fields <jfi...@austininstruments.com> wrote:
>On Wed, 30 Dec 2009 14:28:58 -0600, neve...@GOODEVEca.net (Pete)
>wrote:
>
>>In article <vevmj5hcoigs0iqn2...@4ax.com>,
>>John Fields <jfi...@austininstruments.com> wrote:
>>>What they're talking about is a _turn-off_ surge, so I suspect that 20
>>>second wait will allow the thing to do whatever it needs to in order to
>>>do a soft turn-off.
>>Turn *off* surge?? Where would that happen? I suppose there could be
>>thermal shock as another poster suggested but otherwise I can't see
>>what a sudden current cut-off could do.
>
>---
> L dI
>E = ------
> dt
in such a circuit, and any stray should be minuscule. (It's not even
dependent on being a 'wind-up' unit -- the others I see advertised are
all battery driven.)
>---
>
>Take one apart and post what you find in it?
Maybe eventually (:-)) but I don't really want to offend the present
giver that soon! I may try to write the supplier and see if they can
refer me to a useful source. [Some hope...]
Anyway, thanks everyone for the suggestions.
John Fields
wrote:
>In article <3ounj55128hptu8eo...@4ax.com>,
>John Fields <jfi...@austininstruments.com> wrote:
>>On Wed, 30 Dec 2009 14:28:58 -0600, neve...@GOODEVEca.net (Pete)
>>wrote:
>>
>>>In article <vevmj5hcoigs0iqn2...@4ax.com>,
>>>John Fields <jfi...@austininstruments.com> wrote:
>>>>What they're talking about is a _turn-off_ surge, so I suspect that 20
>>>>second wait will allow the thing to do whatever it needs to in order to
>>>>do a soft turn-off.
>>>Turn *off* surge?? Where would that happen? I suppose there could be
>>>thermal shock as another poster suggested but otherwise I can't see
>>>what a sudden current cut-off could do.
>>
>>---
>> L dI
>>E = ------
>> dt
>Yabbut... inductance? Where? Can't see any possible need for that
>in such a circuit,
---
Not trying to be confrontational, but until you take one apart or
otherwise find out definitively how the thing works, your inability to
see why an inductance might be used is unimportant.
In a wind-up or a shake one, what do you think is generating the
electricity to drive the LEDs?
---
>and any stray should be minuscule. (It's not even
>dependent on being a 'wind-up' unit -- the others I see advertised are
>all battery driven.)
---
Then I suspect that what might be happening is that, because of the
design, the miniscule inductance is generating a spike higher than the
reverse voltage of 7 volts or so allowed across the LED(s).
---
>>Take one apart and post what you find in it?
>
>Maybe eventually (:-)) but I don't really want to offend the present
>giver that soon! I may try to write the supplier and see if they can
>refer me to a useful source. [Some hope...]
---
So buy one and take it apart...
JF
John Fields
<use...@spam.zootal.nospam.com> wrote:
>I've seen lasers that had a life rated in the number of power cycles, not
>how many hours it operated. If you turned it on and left it on, it would run
>for a million years. If you power cycle it every five minutes, it would be
>dead in a week.
---
Kinda like airplane tires...
AIUI, they're rated in "landings"
JF
ian field
"Pete" <neve...@GOODEVEca.net> wrote in message
news:duCdnQ7zT7I9A6TW...@lmi.net...
>
> LED torch (flashlight) I just got for Christmas. It says:
>
> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
> turning ON & OFF. Do not turn ON & OFF repeatedly."
>
> Hunh...? I can't imagine what effect that would have on LEDs. There's
> no turn-on surge like an incandescent would have. How could the life
> be shortened?
>
> I searched the web for that message, and find a number of apparently
> quite different and independent products with the same warning -- all,
> interestingly from UK suppliers! (Though my unit is made in China.)
> Could this be some kind of weirdly spreading myth?
The same thing on gadgets from the Lidl chain of stores (mostly made in
Germany) its nothing unusual to find senseless warnings like not to cover
ventilation grilles on products that don't have any and electric shock
warnings on battery powered gadgets that run on 18V or less, that's just 2 I
can think of off hand!
mister_...@the-newzgroups.com
If you ask me, it's there so that if you're flashlite quits working,
they can refuse to give a replacement or refund by stating that you
turned it on and off improperly. In other words, an excuse to screw
the customer.
Brian Gregory [UK]
news:duCdnQ7zT7I9A6TW...@lmi.net...
>
> LED torch (flashlight) I just got for Christmas. It says:
>
> "IMPORTANT: To extend the life of the LEDs allow 20 seconds between
> turning ON & OFF. Do not turn ON & OFF repeatedly."
>
> Hunh...? I can't imagine what effect that would have on LEDs. There's
> no turn-on surge like an incandescent would have. How could the life
> be shortened?
>
> I searched the web for that message, and find a number of apparently
> quite different and independent products with the same warning -- all,
> interestingly from UK suppliers! (Though my unit is made in China.)
> Could this be some kind of weirdly spreading myth?
A well designed LED torch has a DC-DC converter driving the LED(s) so that
you can use most of the energy in the batteries without the LEDs dimming too
much.
If you just use a series resistor you either have the LED dimming a lot
before the batteries are dead or you end up wasting a lot of energy in the
resistor, or both.
So it could be a requirement of the DC-DC converter rather than the LEDs.
However it still seems rather odd.
--
Brian Gregory. (In the UK)
n...@bgdsv.co.uk
To email me remove the letter vee.