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Long-lasting LED!

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grahamrounce
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Posted on Wednesday, 15 July, 2015 - 09:36 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

You can now get party balloons which are lit up from the inside by an LED.
After bursting one, I had a look at the little unit that lights up. It has two LR41's in series and a blue LED. Bending out a pin of the LED to measure the current showed about 14mA.
But it's been going, admittedly losing some brightness, since Friday evening - over 100 hours now, ie 1400mA hours. The capacity of an LR41 is supposed to be 30mA hours!
Is this possible? :-)

(Message edited by GrahamRounce on 15 July, 2015)
(All my sticks seem to have two wrong ends)
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cjay
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Posted on Wednesday, 15 July, 2015 - 01:18 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I know the balloons you have, I've bought lots of them and my experience is similar, they will illuminate the LED albeit at much reduced brightness for many hours longer than the claimed life.

I'd suggest that the current being drawn now has diminished significantly, LEDs can and do illuminate visibly on microamps.
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grahamrounce
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Posted on Wednesday, 15 July, 2015 - 01:30 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Yes, maybe the off time (less than a minute?) while the probes were being attached gave the batteries a chance to recover a little? I'll try it again, leaving the probes attached for a while.
Interesting about the micro-amps. Is the efficency higher at low current?
(All my sticks seem to have two wrong ends)
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grahamrounce
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Posted on Monday, 20 July, 2015 - 10:37 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It's now on 1.7v, 10uA. Still a clearly visible little dot.

So that's 1.7uW. Normal running would be say 3v, 20mA = 60,000uW!

Power consumption is 1/35000 of normal. I must say it looks like more than 1/35000 of the normal brightness, though it's hard to tell really, not knowing the eye's sensitivity to low levels (probably high).
Does anyone happen to know if LED efficiency increases as power and output go down? Interesting.
(All my sticks seem to have two wrong ends)
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cjay
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Posted on Tuesday, 21 July, 2015 - 12:34 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

LEDs aren't linear output, there's a PWM tutorial for PIC devices that explains it but I suspect the datasheets would also show luminous output characteristics vs current consumption.

Those little LEDs are very impressive, interesting colours and shapes too.
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grahamrounce
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Posted on Tuesday, 21 July, 2015 - 08:48 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I think a comparison with PWM might be misleading, as the power/brightness during the "on" part of the cycle is the full whack.
But now you've mentioned it, a difference in efficiency might be shown up by comparing the apparent brightness of an LED on a 1:35000 PWM cycle with that of one running constantly as above?
(All my sticks seem to have two wrong ends)
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armadillo
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Posted on Tuesday, 21 July, 2015 - 11:37 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

"So that's 1.7uW"

Or 17µW even

There's no such thing as gravity..........
The earth sucks!
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grahamrounce
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Posted on Tuesday, 21 July, 2015 - 12:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Whatever. To continue...
(All my sticks seem to have two wrong ends)
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gordon
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Posted on Tuesday, 21 July, 2015 - 11:23 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Not sure about if PWM is used, but the led graphs of light output v current are pretty linear. There might be some variation of this at very low or very high currents. The other factor is the eye response to brightness is logarithmic, so the led current would need to change quite a bit before a big change in brightness is noticed.
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grahamrounce
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Posted on Tuesday, 04 August, 2015 - 01:39 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It's still going! Dim but visible in normal light.



(Message edited by GrahamRounce on 04 August, 2015)
(All my sticks seem to have two wrong ends)
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grahamrounce
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Posted on Thursday, 13 August, 2015 - 09:56 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ditto
(All my sticks seem to have two wrong ends)
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cjay
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Posted on Friday, 14 August, 2015 - 12:03 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

They're mightily impressive.
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grahamrounce
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Posted on Wednesday, 24 February, 2016 - 01:32 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Update: Still visible, as a tiny dim dot in a darkened room, after seven continuous months!
(All my sticks seem to have two wrong ends)
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grahamrounce
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Posted on Saturday, 16 April, 2016 - 06:39 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I knocked it all over a week ago, and just got round to reconnecting yesterday. So the batteries have had a little holiday, and it seems to have done them good! The dim blue dot is visible even if the room's not totally dark, and without having to wait for my eyes to adjust.
Do these batteries recover like that?
The current doesn't register at all on the 100uA range of my 30,000 ohms/volt meter.
(All my sticks seem to have two wrong ends)
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grahamrounce
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Posted on Wednesday, 01 June, 2016 - 09:44 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

...and still going, dim but quite visible!
(All my sticks seem to have two wrong ends)
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bowden_p
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Posted on Wednesday, 01 June, 2016 - 11:44 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Graham,
I believe some LEDs are slightly photo-voltaic - is it this effect that's keeping the light working so long? ( Daylight slightly "charging" the LR41 batteries during daylight hours?)

I don't know whether you have the light stored in a light-proof box when not being checked?

Just a thought, Paul.
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grahamrounce
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Posted on Monday, 22 August, 2016 - 03:28 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Paul - I'm a little late catching up on this, but after your post I checked that a (different) LED produced some current in the light, which it indeed did.
Then I put the setup in a usually-dark cupboard with an upturned opaque container over it. I looked last night, and it's still glowing dimly..
(All my sticks seem to have two wrong ends)
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grahamrounce
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Posted on Saturday, 24 September, 2016 - 12:55 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

A year and two months on: Still as dim, still as visible!



(Message edited by GrahamRounce on 24 September, 2016)
(All my sticks seem to have two wrong ends)
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bowden_p
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Posted on Thursday, 27 October, 2016 - 04:07 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Graham,
Your LED observation experiment seems quite puzzling to me. I can't understand why the battery appears to be holding up enough voltage to output any current for so long. I would have thought that it would have gone completely zero volts by now.

My initial thought of some photo-voltaic input is discounted, so is it possible that you are in an RF "hot-spot", perhaps from a mobile phone mast, TV repeater or similar? The RF energy keeping the LED circuitry alive. I wonder what happens if you replace the battery with a germanium point contact diode?

On a parallel line, I was chatting with a friend recently. He has fitted LED mains bulbs throughout his house, and had a problem with a chandelier, having 3 bulbs. When he turned the chandelier off, it didn't completely go out, but remained bright enough for long enough to attract a complaint from his wife.

On investigation there was no problem with the mains circuit or switch. He contacted the manufacturer who advised him to replace one of the bulbs with a standard incandescent bulb, which "fixed" the problem, albeit now at extra running cost. Single bulb light fittings with the LED bulbs didn't show this "feature" when switched off, but promptly turned off.

Just shows that LEDs and electronics can behave very oddly at times !

With regards, Paul.
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741
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Posted on Thursday, 27 October, 2016 - 09:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Paul - I can see an LED 'bulb' might retain some charge in its circuitry sufficient to keep the LEDs glowing - but with multiple bulbs (3 in your example), I'd have guessed something like charge trebled, but load trebled - so no difference between a single and a chandelier.

What then is it about multiple parallel LED fittings that gives this effect? Presumably the LED bulbs are in parallel?
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grahamrounce
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Posted on Friday, 28 October, 2016 - 01:33 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Still glowing very dimly.
Fyi, a pic of the sophisticated experimental arrangement, and one of the nornally-dark cupboard. It's under the upside-down hot chocolate container.
I included the microwave, just in case, but it's only been in that cupboard since the photoelectrical suggestion.
As far as I know, there aren't any rf sources nearby, though I'll have a look at the roofs of the flats opposite.
I'm inclined to just think that the led must be highly efficient at very low emission levels, though it's hard to check as the current is too low for my multimeter and in any case I've no idea how to measure such a tiny light level!
Anyone want to invest in an LED balloon to see for themselves?
g
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grahamrounce
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Posted on Friday, 28 October, 2016 - 01:43 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Trying again with the pics
The arrangementThe cupboard
g
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gizo
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Posted on Friday, 28 October, 2016 - 03:06 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Has that alligator lead always been there?
Looks like a pretty big inductor.....
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grahamrounce
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Posted on Friday, 28 October, 2016 - 09:34 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Well, very true! I'll minimise the whole thing and report back. Still interesting, I suppose, if it is that. The LED will do the rectifying of mains hum? The next step: without the battery!
g
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bowden_p
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Posted on Friday, 28 October, 2016 - 12:42 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi 741,
I'll inquire as to whether the chandelier needed any re-wiring, but I don't think it did. The LED bulbs are usually sold as straight replacements of the old incandescent or CFL bulbs, although many don't work with dimmers.

With regards, Paul.
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bowden_p
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Posted on Friday, 28 October, 2016 - 02:46 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Graham,
Is that a mains powered clock/radio on top of the microwave ? Does it have a transformer in it? Perhaps it is coupling to the coiled lead, as gizo implies!
With regards, Paul.
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grahamrounce
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Posted on Friday, 28 October, 2016 - 04:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Paul - No, as a matter of fact it's the 'GrannyGram', derived from the PEE wav player of a while back. It runs off a 12v adapter.
g
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rob_guyer
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Posted on Friday, 28 October, 2016 - 11:47 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

An idle thought. If the residual light is from mains EMI , a few seconds of video captured by a digital camera fitted with macro focus might show stroboscopic effects?
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grahamrounce
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Posted on Saturday, 29 October, 2016 - 08:17 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Oh well, it was a thought... In the pic:
Left: Battery excluded - no glow :-)
Right: Alternate setup - no glow
The variable speed motor with a slotted disc attached, to try and see if the led is going on and off, is in the queue.
g
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grahamrounce
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Posted on Saturday, 29 October, 2016 - 08:23 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

2 variations
g
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grahamrounce
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Posted on Saturday, 26 November, 2016 - 10:47 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Fyi, still very dimly glowing.
g
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grahamrounce
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Posted on Saturday, 07 January, 2017 - 07:49 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Fyi, it's still going strong. Well, not exactly strong, but visible in the dark.
g
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741
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Posted on Saturday, 07 January, 2017 - 10:44 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Bearing in mind what cjay said LEDs can and do illuminate visibly on microamps, then I guess this longevity makes some sense.

Also: The LED has some nominal forward votage, but like all diodes it's not a well defined thing. It's maybe that tiny voltage range, eg 2.1...2.101 or whatever, at which the exponential curve of I/V (smooth all the way to zero V, zero A) goes through a range of currents which make the LED change from "barely visible in daylight" to "clearly visible".

Incidentally: What is the battery voltage with the LED attached?
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grahamrounce
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Posted on Wednesday, 11 January, 2017 - 03:36 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi, @741: It's 2.26v
g
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741
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Posted on Wednesday, 11 January, 2017 - 04:05 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Graham -

So, each cell is only 0.37 below nominal. It'd be interesting to monitor that voltage over time.

(Out of interest: Is there a resistor somewhere in the circuit?)


The other thing that may be worth trying is to rig up an op-amp follower, and gradually raise the level up from 2.6V.

Note how the brightness varies, and at what voltage/brightness you see any sign of 'detectable current' on your meter.

I bet it could be a pretty healthy glow at 0.5mA.
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grahamrounce
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Posted on Wednesday, 11 January, 2017 - 06:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi. No, no resistor, just the two cells and the led.
I'd really like to measure the current somehow. I saw somewhere on the inet someone suggesting a digital multimeter on the volts range inserted series-wise in the circuit. Assuming a megohm for the resistance, you can work out the current, but I haven't tried it yet.
Being able to measure the light output would also be good, to try and guess the relative efficiency, but I've no idea how!
Thanks,
g
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gordon
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Posted on Wednesday, 11 January, 2017 - 08:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

This link might be of interest. Seems that you can still see a blue led with a few tens of nano amps flowing.

http://nerdralph.blogspot.co.uk/2016/01/led-low-power-limbo-light-below-1ua.html
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741
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Posted on Thursday, 12 January, 2017 - 10:03 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Can you use the normal op-amp way of measuring current?

I=Vout/Ro.

Likely I've over-simplified this: The current is so low it may be something more sophisticated is needed.

I Measure
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grahamrounce
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Posted on Thursday, 12 January, 2017 - 10:25 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@Gordon: Yes, very interesting! Some people are more zealous in their investigations..!
g
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grahamrounce
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Posted on Thursday, 12 January, 2017 - 10:35 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

@Gordon: Yes, very interesting! Some people are more zealous in their investigations..!

Using the digital multimeter method above (effectively inserting a 1M resistor) the volts showed as 36mV, giving the current as 36nA.
g
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grahamrounce
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Posted on Thursday, 12 January, 2017 - 10:48 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

A 30mAH battery would supply 36nA for about 95 years! I'll have to pass the experiment on to my grandchildren. Or, perhaps as much interest as possible has been gleaned, so I can put it all in the bin at last :-)
g
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twintub
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Posted on Friday, 13 January, 2017 - 12:12 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

1M?
DMMs are usually 10M aren't they?
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grahamrounce
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Posted on Friday, 13 January, 2017 - 02:41 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

It's an L4950 DMM from Am-Tech. I can't find the specs anywhere (anyone?), but I did a test of the 200mV range with a moving coil MM measuring resistance. It read 1M with the leads one way round, and 0 the other way! So I took it as 1M, like in the original suggestion.
g

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