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How long bright flashing LED last on AA cells?
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Lostgallifreyan
electronics forum Guru Wannabe


Joined: 13 Apr 2006
Posts: 241

PostPosted: Tue Jul 04, 2006 12:17 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Clive Mitchell <bigclive1@ntlworld.com> wrote:
Quote:
In message <12aichk5ihf6509@corp.supernews.com>,
=?UTF-8?B?UGFsaW5kcuKYu21l?= <me9@privacy.net> writes
All that was clear was that he wanted a bright LED to flash and wanted
to power it from, ideally one, but if necessary more, AA NiMH cells -
and was concerned how long it would keep flashing. The logical
inference was that he wanted it to flash for as long as possible.

He know knows that, if he wants, he can keep the LED flashing for
months of a single AA NiMH cell...which I think rather answers his
question. Perhaps. ;)

I'll have a guess at the application.....

They probably wanted to add a flashing LED to a fake camera that could
run for a long time on a battery.

In reality, a short duty cycle blinking LED on a camera immediately says
FAKE! :)



If that's true, it won't deter a thief. Bear with me here, the logic gets
interesting.. >:)

If it won't deter a thief, it's very important that cameras with flashing LED's
on them actually contain lenses and working circuits to gather video evidence
of the events that they might seem to encourage. Therefore it makes sense to
always have something real in there, so in practise, you'd be wrong. :)

In the end it comes down to two types of criminal (occupying various points on
a single line continuum actually). Smart, and dumb. The smart ones will think
this logic through and know that there is no easy guide, a small stub sticking
out the top might be a radio aerial that sends a keep-alive pulse that would
set an alarm off if it was sabotaged to prevent transmission, so a lack of
wires would deter a smart criminal, but not a very stupid one.

So, the LED makes sense, it will deter the smart ones, who will usually have
easier ways to make a dishonest living, and there's not much you can do about
the dumb ones, they're hard to predict. They're usually opportunists though, so
if everything else looks like a deterrent too, they'll leave well alone. I've
had an empty bell-box on a wall over my window for 20 years, and it works, I've
even overheard discussions outside once, and the general tenor was one of
nervous defiance, but the nervousness won out.

If it looks like a duck, how long do you wait to see if it quacks like a duck?
The longer you wait, the more uncertain you get, and uncertainty undermines
resolve, especially of criminals.

And that, ladies and gentlemen, ends my self-amusing rant for the day. >Smile
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ehsjr
electronics forum Guru


Joined: 03 May 2005
Posts: 863

PostPosted: Tue Jul 04, 2006 2:11 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Victor Roberts wrote:
Quote:
On Sat, 01 Jul 2006 19:57:53 +0100, Jaxx <nonono@co.co.co
wrote:


Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?


I'm surprised that so many people have an answer when you
have not told us how much current this LED will draw in your
application.

Did you read the answers? Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?

I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?

Ed
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Victor Roberts
electronics forum beginner


Joined: 20 Jul 2005
Posts: 40

PostPosted: Tue Jul 04, 2006 2:33 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

On Tue, 04 Jul 2006 02:11:29 GMT, ehsjr
<ehsjr@bellatlantic.net> wrote:

Quote:
Victor Roberts wrote:
On Sat, 01 Jul 2006 19:57:53 +0100, Jaxx <nonono@co.co.co
wrote:


Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?


I'm surprised that so many people have an answer when you
have not told us how much current this LED will draw in your
application.

Did you read the answers?

Yes.

Quote:
Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?

All of them - because the OP did not tell us the current.

Quote:
I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?

The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
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Lostgallifreyan
electronics forum Guru Wannabe


Joined: 13 Apr 2006
Posts: 241

PostPosted: Tue Jul 04, 2006 4:02 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Victor Roberts <xxx@lighting-research.com> wrote:
Quote:
On Tue, 04 Jul 2006 02:11:29 GMT, ehsjr
ehsjr@bellatlantic.net> wrote:

Victor Roberts wrote:
On Sat, 01 Jul 2006 19:57:53 +0100, Jaxx <nonono@co.co.co
wrote:


Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?


I'm surprised that so many people have an answer when you
have not told us how much current this LED will draw in your
application.

Did you read the answers?

Yes.

Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?

All of them - because the OP did not tell us the current.

I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?

The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.



Doesn't matter though, there are two ways to go, either demand exact specs from
someone who might not have a clear idea yet, or post a response based on your
own carefully judged assumption. The latter is usually easier that waiting and
second-guessing your response before you've made one, and it gives the OP
something to think about. If the result is confusion and an apparent grasping
at each offered straw in turn, then it is probably wise to demand some kind of
focussed assessment of the original situation. At least this way the OP is not
considered stupid until proven intelligent. :)


My own thoughts on the topic are: you can have a 'super-bright' LED and long
life, but a few things should be managed to do it. Use a lithium battery
preferably, then alkaline, and avoid Nimh types. Use a power converter to
efficiently make use of the entire battery charge. Use a narrow viewing angle
on the LED, so that it projects strongly for only a limited point of view. Use
a clear LED not a coloured plastic. Use a short duty cycle, less than 1% and
pulse length no longer than 50 milliseconds even when the flash period is
longer than 5 seconds, with that period never being longer than 10 seconds
unless you're really going to be staring at that LED for 30 seconds or more
regardless of what it might be doing. These are not hard and fast rules. :)

Lastly, consider a low power laser diode, UNLENSED. These are eye safe at
distances beyond a few inches, (take care NOT to use a microlensed version
though) as they diverge strongly. Their output is highly monochromatic,
specular, very eye-catching, and their conversion of electricity to light is
second to none, so they can make ideal beacons. They're much harder to use
though, easily damaged, and initial power requirements are higher. Also, while
you can make an LED stand much higher currents than their nominal rating, often
tenfold increase, with a laser diode, the pulse rating for a CW diode is
usually less than twofold higher.
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Don Klipstein
electronics forum Guru Wannabe


Joined: 02 May 2005
Posts: 297

PostPosted: Tue Jul 04, 2006 4:03 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

In article <part1of1.1.npyOs#fJ2qhlxA@ue.ph>, Lostgallifreyan wrote:
Quote:
Clive Mitchell <bigclive1@ntlworld.com> wrote:

I'll have a guess at the application.....

They probably wanted to add a flashing LED to a fake camera that could
run for a long time on a battery.

In reality, a short duty cycle blinking LED on a camera immediately says
FAKE! :)

If that's true, it won't deter a thief. Bear with me here, the logic gets
interesting.. >:)

If it won't deter a thief, it's very important that cameras with flashing
LEDs on them actually contain lenses and working circuits to gather video
evidence of the events that they might seem to encourage. Therefore it
makes sense to always have something real in there, so in practise, you'd
be wrong. Smile

I have some ideas...

1. If this is to be used in the home, power the LED from a wall wart.
And maybe power the LED through two steering diodes coming together - one
from the wall wart and the other from a backup battery.
For that matter, get the cheapest actual security camera you can find
from a hobbyist/surplus catalog - even if it's incompatible with anything
practical.
Or further for that matter, find some little professional looking case
and fit some cheap webcam into it and you have a fake security camera that
may actually be made to work in some way as a real one! Put a red LED on
the case...

2. I have an idea for the red LED - make it glow continuously like those
on real cameras that have LEDs do. Get a GaAlAsP red LED, peak
wavelength 660 nm, 3000 mcd (with a usual beam width of 15 degrees but
sometimes claimed more), such as Radio Shack 276-307. Red LEDs of
same/similar chemistry and efficiency are Agilent HLMP-8103 and HLMP-C124.
Get some fine sandpaper and sand down the tip by about a millimeter,
then restore the "bullet" shape but about a millimeter shorter and with
the tip very slightly more blunt, then get some really fine sandpaper and
get the LED good and evenly frosted. After that, you have a super high
efficiency diffused wide angle red LED that works well and reliably at 1
milliamp, and may be bright enough at half a milliamp. It will glow with
a color close enough to that of lower efficiency red LEDs.

If you really want to go all out, get an InGaN green LED (nominal
wavelength usually 525 to 530 nm) of the common 5 mm "bullet" style and
give it the sandpaper treatment described above. Then give it half a
milliamp or maybe a quarter of a milliamp. Most Nichia 5 mm green ones
and those trying to compete with them (ETG, and others) should at half a
milliamp have a brightness that I consider "fully that of a usual green
LED indicator light". Furthermore, the wavelength of these tends to shift
a little inversely with current, and at half a milliamp the color is
likely to be about that of LEDs with nominal wavelength in the 550's nm,
maybe close to 560 - a yellowish shade of green likely to look enough like
a usual 565 nm green LED indicator lamp to look like a usual indicator LED
to most criminals.

A pack of (4) AA alkaline cells with a 6.8K resistor should power such a
green LED reasonably well 24/7 for at least half a year.

If you want an LED to falsely indicate presence of a security system in
an automobile, don't worry about conserving every milliamp since the
battery has self-discharge in the 10's of milliamps. You can afford a few
milliamps to protect a car.

- Don Klipstein (don@misty.com)
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Palindr☻me
electronics forum addict


Joined: 10 May 2005
Posts: 76

PostPosted: Tue Jul 04, 2006 8:30 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Victor Roberts wrote:
Quote:
On Tue, 04 Jul 2006 02:11:29 GMT, ehsjr
ehsjr@bellatlantic.net> wrote:


Victor Roberts wrote:

On Sat, 01 Jul 2006 19:57:53 +0100, Jaxx <nonono@co.co.co
wrote:



Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?


I'm surprised that so many people have an answer when you
have not told us how much current this LED will draw in your
application.

Did you read the answers?


Yes.


Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?


All of them - because the OP did not tell us the current.


I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?


The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.


IME,YMMV, almost all OPs contain insufficent information to be certain
of the requirement.

Now in many cases, where safety and/or the law is involved, all a
respondent can do is to ask for more information. AS an example, when
someone asks about domestic electrical wiring and how to do something -
it cannot be answered without knowing where they are and what
regulations apply. So, if uncertain, the only response can be "Where are
you?"

With posts where safety and/or law aren't immediately involved,
responding to everything with "insufficient information, please clarify"
makes sense but is a tad boring - treating the information as clues to a
puzzle is more fun..It is never possible to eliminate the "ass" in
assumptions - but no harm is done. Putting the clues together correctly
can be a bit like doing the Times crossword..

I would imagine that most posters here enjoy solving puzzles and trying
to produce the answer that they think the OP would have got, had he
given enough information to be certain...

--
Sue
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nospam
electronics forum addict


Joined: 14 Feb 2005
Posts: 86

PostPosted: Tue Jul 04, 2006 9:24 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Lostgallifreyan <no-one@nowhere.net> wrote:

Quote:
The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.

Doesn't matter though, there are two ways to go, either demand exact specs from
someone who might not have a clear idea yet, or post a response based on your
own carefully judged assumption. The latter is usually easier that waiting and
second-guessing your response before you've made one, and it gives the OP
something to think about.

A third and the easiest way to go is ignore dumb questions like "I have an
application for some string, what length do I need?".

Dumb questions like this often generate long threads of, frankly, dumb
answers.

The OP remains notable by his absence. If the OP can't be bothered to ask
properly why do so many feel inclined to answer?

Perhaps it is because letting the reader choose the question allows them to
pick one they have an answer for.
--
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Clive Mitchell
electronics forum beginner


Joined: 25 Mar 2005
Posts: 18

PostPosted: Tue Jul 04, 2006 9:34 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

In message <slrneajq4f.3tc.don@manx.misty.com>, Don Klipstein
<don@manx.misty.com> writes
Quote:
If you really want to go all out, get an InGaN green LED (nominal
wavelength usually 525 to 530 nm) of the common 5 mm "bullet" style and
give it the sandpaper treatment described above. Then give it half a
milliamp or maybe a quarter of a milliamp. Most Nichia 5 mm green ones
and those trying to compete with them (ETG, and others) should at half
a milliamp have a brightness that I consider "fully that of a usual
green LED indicator light". Furthermore, the wavelength of these tends
to shift a little inversely with current, and at half a milliamp the
color is likely to be about that of LEDs with nominal wavelength in the
550's nm, maybe close to 560 - a yellowish shade of green likely to
look enough like a usual 565 nm green LED indicator lamp to look like a
usual indicator LED to most criminals.

I was demonstrating the efficiency of Gallium Nitride green LEDs to a
friend yesterday. I plugged it in to a simple tester that runs the LED
at either 75uA or 20mA and showed him it lit at 75uA. I was surprised
myself when I saw the beam actually move across his face as I pointed it
at him.

Given the distance most people are from a camera I would say that filing
it down is not required.

A set of four or more AA Alkalines with a suitable resistor (39K?)
should theoretically keep the Gallium Nitride green LED glowing at 75uA
for about three years.

--
Clive Mitchell
http://www.bigclive.com
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William P.N. Smith
electronics forum addict


Joined: 02 Nov 2005
Posts: 80

PostPosted: Tue Jul 04, 2006 12:50 pm    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Lostgallifreyan <no-one@nowhere.net> wrote:
Quote:
If it looks like a duck, how long do you wait to see if it quacks like a duck?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94030
works remarkably well, it senses motion and scans while flashing a
light.
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William P.N. Smith
electronics forum addict


Joined: 02 Nov 2005
Posts: 80

PostPosted: Tue Jul 04, 2006 1:22 pm    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

nospam <nospam@please.invalid> wrote:
Quote:
A third and the easiest way to go is ignore dumb questions like "I have an
application for some string, what length do I need?".

Thank you for your input.
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William P.N. Smith
electronics forum addict


Joined: 02 Nov 2005
Posts: 80

PostPosted: Tue Jul 04, 2006 1:24 pm    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Lostgallifreyan <no-one@nowhere.net> wrote:
Quote:
Doesn't matter though, there are two ways to go, either demand exact specs from
someone who might not have a clear idea yet, or post a response based on your
own carefully judged assumption.

Yeah, what "Lost" said.

Quote:
Lastly, consider a low power laser diode, UNLENSED. These are eye safe at
distances beyond a few inches, (take care NOT to use a microlensed version
though) as they diverge strongly. Their output is highly monochromatic,
specular, very eye-catching, and their conversion of electricity to light is
second to none, so they can make ideal beacons.

This sounds interesting, do you have any sources?

Thanks!

[I think the discussion engendered by this particular "How long a
piece of string?" query has been useful and enlightening [sic].]
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Bob
electronics forum beginner


Joined: 30 Oct 2005
Posts: 17

PostPosted: Tue Jul 04, 2006 1:30 pm    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

"Victor Roberts" <xxx@lighting-research.com> wrote in message
news:lnkja2pfnu2btq9e6pqd5dm94q4h2imdc3@4ax.com...
Quote:
On Tue, 04 Jul 2006 02:11:29 GMT, ehsjr
ehsjr@bellatlantic.net> wrote:
On Sat, 01 Jul 2006 19:57:53 +0100, Jaxx <nonono@co.co.co
wrote:


Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?

Did you read the answers?

Yes.

Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?

All of them - because the OP did not tell us the current.

I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?

The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.

--
Vic Roberts

The OP did not provide enough information. In fact, he asked how long an LED
would last - He did not ask how long the cells powering the LED would last.

He did not specify duty cycle. His interpretation of "flashing" could range
from 1/2 second on, 1/2 second off (think traffic signal on flash), which
would likely average 10 ma (20 ma LED / 50% duty cycle) + power consumption
of whatever you are driving it with , down to sub millisecond pulses every
10 seconds, which could result in the cell(s) lasting for their self
discharge life.

He did not say what he would be flashing it with. He could be using a relay
with a capacitor to provide a time constant, which would likely make for a
very short battery life, or, with enough cells in series, and no current
limiting for the LED, could answer the question as to how long the LED would
last (not very long), or he could be using an LM3903.

He could be talking about something like this
http://www.lc-led.com/View/itemNumber/144 Even reading the datasheet for
that device does not provide enough information where you could provide an
accurate answer to either interpretation of the OP's question.


You could change the wording of the original question to address a different
technology, and have similar questions:

Very approximately how long would a lawn mower engine last?
The power source would be one (or more but how many?) gas cans each with a
capacity of 20 liters?


None of this is meant to put down the original poster. He just did not
provide enough info to answer his question without assuming just about
everything about it.
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Palindr☻me
electronics forum addict


Joined: 10 May 2005
Posts: 76

PostPosted: Tue Jul 04, 2006 2:13 pm    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

Bob wrote:
Quote:
"Victor Roberts" <xxx@lighting-research.com> wrote in message
news:lnkja2pfnu2btq9e6pqd5dm94q4h2imdc3@4ax.com...

On Tue, 04 Jul 2006 02:11:29 GMT, ehsjr
ehsjr@bellatlantic.net> wrote:

On Sat, 01 Jul 2006 19:57:53 +0100, Jaxx <nonono@co.co.co
wrote:



Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?


Did you read the answers?

Yes.


Which one(s) did you find
surprising in view of the fact that the op did not
tell us the current requirement?

All of them - because the OP did not tell us the current.


I saw only 1 answer that would have required knowing
the op's current requirement to support the respondent's
conclusion. So I wonder what I am missing?

The answers that didn't require knowing the OP's current
requirements were probably correct for the assumptions made
by the responder, but not specific to the OP's question.

--
Vic Roberts


The OP did not provide enough information. In fact, he asked how long an LED
would last - He did not ask how long the cells powering the LED would last.

He did not specify duty cycle. His interpretation of "flashing" could range
from 1/2 second on, 1/2 second off (think traffic signal on flash), which
would likely average 10 ma (20 ma LED / 50% duty cycle) + power consumption
of whatever you are driving it with , down to sub millisecond pulses every
10 seconds, which could result in the cell(s) lasting for their self
discharge life.

He did not say what he would be flashing it with. He could be using a relay
with a capacitor to provide a time constant, which would likely make for a
very short battery life, or, with enough cells in series, and no current
limiting for the LED, could answer the question as to how long the LED would
last (not very long), or he could be using an LM3903.

He could be talking about something like this
http://www.lc-led.com/View/itemNumber/144 Even reading the datasheet for
that device does not provide enough information where you could provide an
accurate answer to either interpretation of the OP's question.


You could change the wording of the original question to address a different
technology, and have similar questions:

Very approximately how long would a lawn mower engine last?
The power source would be one (or more but how many?) gas cans each with a
capacity of 20 liters?


None of this is meant to put down the original poster. He just did not
provide enough info to answer his question without assuming just about
everything about it.


Yes but it is fun guess-timating what he had in mind... Incidently,

indefinately - I can never start the bloody thing unless I have someone
to hold the thing down whilst I pull on the cord with both hands...


--
Sue
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JohnR66
electronics forum addict


Joined: 13 Apr 2006
Posts: 61

PostPosted: Wed Jul 05, 2006 1:23 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

"Jaxx" <nonono@co.co.co> wrote in message
news:Xns97F3CB17CDB991F3E91@127.0.0.1...
Quote:
Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?

You asked how long the LED would last. Did you mean whow long the batteries
would last?

The LED can last a second to many years depending on the dropping resistor
or the lack thereof.
John
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Palindr☻me
electronics forum addict


Joined: 10 May 2005
Posts: 76

PostPosted: Wed Jul 05, 2006 6:02 am    Post subject: Re: How long bright flashing LED last on AA cells? Reply with quote

JohnR66 wrote:
Quote:
"Jaxx" <nonono@co.co.co> wrote in message
news:Xns97F3CB17CDB991F3E91@127.0.0.1...

Very approximetely how long would a single super-bright red flashing LED
last?

The power source would be one (or more but how many?) rechargeable NiMH
AA cells each with a capacity of 1000 mAh?


You asked how long the LED would last. Did you mean whow long the batteries
would last?

The LED can last a second to many years depending on the dropping resistor
or the lack thereof.

The OP also didn't indicate the environment. Did he mean at normal room
temperatures?

The LED can last a few seconds to many years, depending on being located
inside the central heating furnace, or outside it...

--
Sue
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