I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?

On Friday, 23 December 2016 16:24:56 UTC, ss wrote:
I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?

Yes, but dimmer.


NT

On 23/12/2016 17:57, wrote:
On Friday, 23 December 2016 16:24:56 UTC, ss wrote:
I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?

Yes, but dimmer.


NT

ok, thanks

I would suspect they will in most cases, but obviously one might expect them
to be a bit dimmer.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

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"ss" wrote in message
news
I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?

On Fri, 23 Dec 2016 16:24:43 +0000, ss wrote:

I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?

I've at least a dozen torches and push-switch lights that are running on
NiMH and they are pretty good. With luck, the lower voltage will prolong the
LEDs' lives.
One torch can bee seen shining on a pale object about 100 yds away - enough
for most prposes.
The Oral-B toothbrush goes for about 5 weeks on a pair of Eneloop Pros, but
I change the cells every month, just as a routine.
--
Peter.
The gods will stay away
whilst religions hold sway

Brian Gaff wrote

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.

If they have been properly designed so they run the leds at full
intensity even when the alkaline has dropped to below 1V, they
wont be any dimmer with nickel metal hydride rechargeable.


"ss" wrote in message
news
I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?

On Sat, 24 Dec 2016 10:01:48 +0000, Brian Gaff wrote:

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.
Brian

Obviously? Why obviously? Most small LEDs turn on at less than one volt
forward voltage and it's the current through them rather than the voltage
across them that is the predominant consideration WRT brightness.
Consequently they may well run less brightly when powered by the non
alkaline cells, but that's due to the difference in the cells' inherent
characteristic internal *resistances* rather than their terminal voltages.

Cursitor Doom wrote:
On Sat, 24 Dec 2016 10:01:48 +0000, Brian Gaff wrote:

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.
Brian

Obviously? Why obviously? Most small LEDs turn on at less than one volt
forward voltage and it's the current through them rather than the voltage
across them that is the predominant consideration WRT brightness.
Consequently they may well run less brightly when powered by the non
alkaline cells, but that's due to the difference in the cells' inherent
characteristic internal *resistances* rather than their terminal voltages.

Hmm. I sort of know what you're saying, but:- It's the voltage across
the LED that will determine the current going through it.

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a
NiMh one.

What I *think* you're saying is that the alkaline cell may well have
a higher internal resistance so that at (say) a current drain of 100mA
its output voltage is *less* that that of the NiMh cell at the same
current.

--
Chris Green
·

On Sat, 24 Dec 2016 22:01:20 +0000, Chris Green wrote:

Hmm. I sort of know what you're saying, but:- It's the voltage across
the LED that will determine the current going through it.

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a NiMh
one.

What I *think* you're saying is that the alkaline cell may well have a
higher internal resistance so that at (say) a current drain of 100mA its
output voltage is *less* that that of the NiMh cell at the same current.

You're really not going to achieve anything useful here by focusing on
the voltage drop across the device which is a function of the diode's
characteristic *barrier height* as opposed to the applied voltage. An
avalanche effect occurs - a sudden rapid increase in current - at an
applied voltage well below the output of either type of cell (could be as
little as 0.6V) so *current* is the dominant criterion we must consider.

On 24/12/16 23:26, Cursitor Doom wrote:
On Sat, 24 Dec 2016 10:01:48 +0000, Brian Gaff wrote:

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.
Brian

Obviously? Why obviously? Most small LEDs turn on at less than one volt
forward voltage

No, they don't.

RED is 1.4v and green is more. Cant remember what blue is. (looks it up)
Oh. 3-4V or more.

Because of the exponential nature of the curve, almost no current will
flow until the turn on threshold is nearly reached.

On 25/12/16 00:34, Cursitor Doom wrote:
On Sat, 24 Dec 2016 22:01:20 +0000, Chris Green wrote:

Hmm. I sort of know what you're saying, but:- It's the voltage across
the LED that will determine the current going through it.

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a NiMh
one.

What I *think* you're saying is that the alkaline cell may well have a
higher internal resistance so that at (say) a current drain of 100mA its
output voltage is *less* that that of the NiMh cell at the same current.

You're really not going to achieve anything useful here by focusing on
the voltage drop across the device which is a function of the diode's
characteristic *barrier height* as opposed to the applied voltage. An
avalanche effect occurs - a sudden rapid increase in current - at an
applied voltage well below the output of either type of cell (could be as
little as 0.6V)

Utter ********.

Almost no current occurs in even an IR LED below 1.2v, and for a blue,
that could be up around 3V+


so *current* is the dominant criterion we must consider.


That bit is correct, but don't expect a blue LED to light up on a single
1.5V battery at all.

Red and amber maybe, but that's about it.

Cursitor Doom wrote:
On Sat, 24 Dec 2016 22:01:20 +0000, Chris Green wrote:

Hmm. I sort of know what you're saying, but:- It's the voltage across
the LED that will determine the current going through it.

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a NiMh
one.

What I *think* you're saying is that the alkaline cell may well have a
higher internal resistance so that at (say) a current drain of 100mA its
output voltage is *less* that that of the NiMh cell at the same current.

You're really not going to achieve anything useful here by focusing on
the voltage drop across the device which is a function of the diode's
characteristic *barrier height* as opposed to the applied voltage. An
avalanche effect occurs - a sudden rapid increase in current - at an
applied voltage well below the output of either type of cell (could be as
little as 0.6V) so *current* is the dominant criterion we must consider.

But it's *still* the voltage across the device that determines the
current going through it. Yes, it's a non-linear device so there is a
'knee' in the current/voltage characteristic but this has no bearing
on the brightness from Alkaline versus NiMh batteries. At a given
voltage the brightness will be the same, if the Alkaline battery puts
a higher voltage across the LED then it will be brighter. The fact
(or not) that the NiMh battery *could* supply more current at a given
voltage makes no difference, the LED will only take the current it
takes at a given voltage.


--
Chris Green
·

On Sun, 25 Dec 2016 20:30:47 +0000, Chris Green wrote:

But it's *still* the voltage across the device that determines the
current going through it. Yes, it's a non-linear device so there is a
'knee' in the current/voltage characteristic but this has no bearing on
the brightness from Alkaline versus NiMh batteries. At a given voltage
the brightness will be the same, if the Alkaline battery puts a higher
voltage across the LED then it will be brighter. The fact (or not) that
the NiMh battery *could* supply more current at a given voltage makes no
difference, the LED will only take the current it takes at a given
voltage.

Yours is a hopeless approach that takes no account of the parameter
spread one encounters with different devices, even those from within the
same batch. This is a common problem we come across all the time in
electronic design. If you have a multimeter with a diode test function,
select a bunch of seemingly identical diodes and test them. You will find
there is a spread of results from maybe 0.65V to say 0.73. Hooking these
up to the same voltage will produce differing brightnesses and quite
possibly destroy those devices with a lower barrier height. OTOH, rigging
up series resistance in accordance with the device's datasheet to limit
the *current* to the same value will guarantee any variation in
brightness between devices to be so small as to be imperceptible and no
devices will be damaged or destroyed. This is the correct approach to
use. Try googling "monte carlo analysis" and you'll soon get the picture.

Cursitor Doom wrote:
On Sun, 25 Dec 2016 20:30:47 +0000, Chris Green wrote:

But it's *still* the voltage across the device that determines the
current going through it. Yes, it's a non-linear device so there is a
'knee' in the current/voltage characteristic but this has no bearing on
the brightness from Alkaline versus NiMh batteries. At a given voltage
the brightness will be the same, if the Alkaline battery puts a higher
voltage across the LED then it will be brighter. The fact (or not) that
the NiMh battery *could* supply more current at a given voltage makes no
difference, the LED will only take the current it takes at a given
voltage.

Yours is a hopeless approach that takes no account of the parameter
spread one encounters with different devices, even those from within the

A hopeless approach to what?

--
Chris Green
·

On Sun, 25 Dec 2016 21:26:19 +0000, Chris Green wrote:

A hopeless approach to what?

A hopeless approach to understanding and predicting the behaviour of
these devices at a fundamental level. With much of electronics it
wouldn't matter, but with diodes and bipolar junction transistors you
really have to consider them from the current perspective, not voltage.

On 26/12/16 00:21, Cursitor Doom wrote:
On Sun, 25 Dec 2016 21:26:19 +0000, Chris Green wrote:

A hopeless approach to what?

A hopeless approach to understanding and predicting the behaviour of
these devices at a fundamental level. With much of electronics it
wouldn't matter, but with diodes and bipolar junction transistors you
really have to consider them from the current perspective, not voltage.

I am beiginning to wonder if tesco have put something in the Xmas sherry.

The number of post claiming outrageously erronous horse**** to be
perfectly true and valid has increased dramatically over the last few days.

Cursitor Doom wrote:
On Sun, 25 Dec 2016 21:26:19 +0000, Chris Green wrote:

A hopeless approach to what?

A hopeless approach to understanding and predicting the behaviour of
these devices at a fundamental level. With much of electronics it
wouldn't matter, but with diodes and bipolar junction transistors you
really have to consider them from the current perspective, not voltage.

That isn't what was being discussed. What originally made me comment
was the idea that somehow (because of its greater current capability)
a NiMh battery would push more current through the LED. I was just
pointing out that for a particular LED the current through the LED
will be the same for a given voltage across the LED, it makes no
difference what current the voltage source is capable of.

I agree that junction transistors and LEDs are 'current' devices, but
that wasn't particularly relevant to my original comment.

--
Chris Green
·

On Sunday, 25 December 2016 20:57:35 UTC, Cursitor Doom wrote:
On Sun, 25 Dec 2016 20:30:47 +0000, Chris Green wrote:

But it's *still* the voltage across the device that determines the
current going through it. Yes, it's a non-linear device so there is a
'knee' in the current/voltage characteristic

yup

but this has no bearing on
the brightness from Alkaline versus NiMh batteries.

of course it has!

At a given voltage
the brightness will be the same, if the Alkaline battery puts a higher
voltage across the LED then it will be brighter. The fact (or not) that
the NiMh battery *could* supply more current at a given voltage makes no
difference, the LED will only take the current it takes at a given
voltage.

That's not really how LEDs work

Yours is a hopeless approach that takes no account of the parameter
spread one encounters with different devices, even those from within the
same batch. This is a common problem we come across all the time in
electronic design. If you have a multimeter with a diode test function,
select a bunch of seemingly identical diodes and test them. You will find
there is a spread of results from maybe 0.65V to say 0.73.

I've done that.
36x Silicon diodes at 0.86mA: 0.540v - 1.350v
3x Germanium diodes: 0.326v 0.329v 0.336v.

Hooking these
up to the same voltage will produce differing brightnesses and quite
possibly destroy those devices with a lower barrier height.

Connecting silicon diodes to anything does not produce any brightness.

OTOH, rigging
up series resistance in accordance with the device's datasheet to limit
the *current* to the same value will guarantee any variation in
brightness between devices to be so small as to be imperceptible

nonsense

and no
devices will be damaged or destroyed. This is the correct approach to
use. Try googling "monte carlo analysis" and you'll soon get the picture.

LEDs are not the same thing as rectifing diodes. LED Vf is about 1.6v - 4v. The LED christmas lights I've used on NiMH instead of alkaline presumably have inbuilt resistance, and all the colours worked fine on both battery types.


NT

wrote:
At a given voltage
the brightness will be the same, if the Alkaline battery puts a higher
voltage across the LED then it will be brighter. The fact (or not) that
the NiMh battery *could* supply more current at a given voltage makes no
difference, the LED will only take the current it takes at a given
voltage.

That's not really how LEDs work

??

--
Chris Green
·

In article ,
Chris Green wrote:
But it's *still* the voltage across the device that determines the
current going through it. Yes, it's a non-linear device so there is a
'knee' in the current/voltage characteristic but this has no bearing
on the brightness from Alkaline versus NiMh batteries. At a given
voltage the brightness will be the same, if the Alkaline battery puts
a higher voltage across the LED then it will be brighter. The fact
(or not) that the NiMh battery *could* supply more current at a given
voltage makes no difference, the LED will only take the current it
takes at a given voltage.

Surely a decent torch would have electronics which drove the LED at
constant current? Easy enough to do these days. So would give a consistent
brightness until the battery was exhausted?

--
*'Progress' and 'Change' are not synonyms.

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 26 Dec 2016 14:40:53 +0000, Dave Plowman (News) wrote:

Surely a decent torch would have electronics which drove the LED at
constant current? Easy enough to do these days. So would give a
consistent brightness until the battery was exhausted?

Yes, in theory. But that regulation doesn't come for free. And it will be
linear regulation not switching so even less efficient. There are losses
involved so the batteries wouldn't last as long as with the "Chinese
Method" of basically just hooking them all up in parallel to a voltage
source and hoping for the best.

On Mon, 26 Dec 2016 14:25:05 +0000, Chris Green wrote:

wrote:
At a given voltage the brightness will be the same, if the Alkaline
battery puts a higher voltage across the LED then it will be
brighter. The fact (or not) that the NiMh battery *could* supply
more current at a given voltage makes no difference, the LED will
only take the current it takes at a given voltage.

That's not really how LEDs work

??

Tabitha has got her quoting mixed up by the look of it; I for one
couldn't make head nor tail of it.

On Monday, 26 December 2016 16:16:28 UTC, Cursitor Doom wrote:
On Mon, 26 Dec 2016 14:25:05 +0000, Chris Green wrote:

tabbypurr wrote:
At a given voltage the brightness will be the same, if the Alkaline
battery puts a higher voltage across the LED then it will be
brighter. The fact (or not) that the NiMh battery *could* supply
more current at a given voltage makes no difference, the LED will
only take the current it takes at a given voltage.

That's not really how LEDs work

??

Tabitha has got her quoting mixed up by the look of it;

nope

I for one
couldn't make head nor tail of it.

no surprise.

On 24/12/2016 22:01, Chris Green wrote:
Cursitor Doom wrote:
On Sat, 24 Dec 2016 10:01:48 +0000, Brian Gaff wrote:

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.
Brian

Obviously? Why obviously? Most small LEDs turn on at less than one volt
forward voltage and it's the current through them rather than the voltage
across them that is the predominant consideration WRT brightness.

Depends what you mean by "turn on".
White LEDs at 5uA typically drop around 2.4v and the die is just visibly
glowing at that. Dark adapted you might see a glimmer at much lower
currents with the latest crop of high efficiency LEDs.

There are quantum limitations on the terminal voltage having to be
1.25v to actually emit a blue photon! Usually I find at least 2v.

Consequently they may well run less brightly when powered by the non
alkaline cells, but that's due to the difference in the cells' inherent
characteristic internal *resistances* rather than their terminal voltages.

Hmm. I sort of know what you're saying, but:- It's the voltage across
the LED that will determine the current going through it.

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a
NiMh one.

But a lot of modern led torches now use a voltage to current converter
chip that takes the battery voltage from a single cell and converts it
to an approximately constant current drive. Outdoor solar powered
nightlights use a similar method to drive their LEDs too.

The result is that the LED will be just as bright but for a shorter
period of time since the device cuts off to protect the battery from
corrosion induced leakage at some minimum terminal voltage.

What I *think* you're saying is that the alkaline cell may well have
a higher internal resistance so that at (say) a current drain of 100mA
its output voltage is *less* that that of the NiMh cell at the same
current.

That internal resistance might matter if the LED was drawing several
amps like a torch with a bright filament bulb does.

--
Regards,
Martin Brown

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a
NiMh one.

Who on earth wrote this nonsense? The attributions have all gone to hell
in a handbasket in this thread ISTM.
You do *not* "fix" the current through an LED by applying a fixed voltage
across it FFS. Haven't any of you thick ****s heard of thermal runaway?
Google it FFS. Physics 101.

On Sun, 25 Dec 2016 05:44:07 +0200, The Natural Philosopher wrote:

You're really not going to achieve anything useful here by focusing on
the voltage drop across the device which is a function of the diode's
characteristic *barrier height* as opposed to the applied voltage. An
avalanche effect occurs - a sudden rapid increase in current - at an
applied voltage well below the output of either type of cell (could be
as little as 0.6V)

Utter ********.

Still ****ed from xmas, NP?

Almost no current occurs in even an IR LED below 1.2v, and for a blue,
that could be up around 3V+

If you'd been sober enough to read and understand the thread properly you
would realise I'm referencing small signal diodes here (0.55-0.72V BH)
for the sake of simplicity in making this comparison - NOT coloured LEDs
(exact same principle but an easier range of values to deal with).

Cursitor Doom wrote:

If there is 1.35 volts across the LED that fixes the current going
through it, the LED doesn't know whether it's an alkaline cell or a
NiMh one.

Who on earth wrote this nonsense? The attributions have all gone to hell
in a handbasket in this thread ISTM.
You do *not* "fix" the current through an LED by applying a fixed voltage
across it FFS. Haven't any of you thick ****s heard of thermal runaway?
Google it FFS. Physics 101.

I wasn't suggesting that one provides a constant voltage source across
the LED. I was just saying that *if* the voltage was 1.35 volts when
the thing was running then it makes no difference if the supply is
from an alkaline cell or a NiMh one. The original 'issue' we were
discussing was how the type of cell might (or might not) affect the
brightness.

--
Chris Green
·

On Wed, 28 Dec 2016 11:23:11 +0000, Chris Green wrote:

I wasn't suggesting that one provides a constant voltage source across
the LED. I was just saying that *if* the voltage was 1.35 volts when
the thing was running then it makes no difference if the supply is from
an alkaline cell or a NiMh one. The original 'issue' we were discussing
was how the type of cell might (or might not) affect the brightness.

I can't recall if it was you or someone else who asserted that a constant
voltage across an LED gives rise to a constant current through it.
Diodes, including LEDs, DO obey Ohms law, of course, but are NOT linear
loads like resistors. The barrier height of these components is
temperature dependent. When you apply a voltage to a diode, the resulting
current generates a heating effect which lowers the barrier height
causing more current to flow which causes more heating and so on. It's a
vicious circle which often leads to the eventual destruction of the
device as it generates more heat than it can dissipate. This can be
avoided by using a current-limiting resistor in series with the LED
calculated to provide the specified forward current the manufacturer
recommends. That's the quick and dirty way of doing it, and it works well
enough in most circumstances, but the proper way to supply LEDs, though,
is from a properly regulated current source.
Hope that's finally cleared that up!

On 12/26/2016 6:09 PM, Martin Brown wrote:
On 24/12/2016 22:01, Chris Green wrote:
Cursitor Doom wrote:
On Sat, 24 Dec 2016 10:01:48 +0000, Brian Gaff wrote:

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.
Brian

Obviously? Why obviously? Most small LEDs turn on at less than one volt
forward voltage and it's the current through them rather than the
voltage
across them that is the predominant consideration WRT brightness.

Depends what you mean by "turn on".
White LEDs at 5uA typically drop around 2.4v and the die is just visibly
glowing at that. Dark adapted you might see a glimmer at much lower
currents with the latest crop of high efficiency LEDs.

There are quantum limitations on the terminal voltage having to be
1.25v to actually emit a blue photon! Usually I find at least 2v.


I'm a bit confused here. It's been ages since I looked at any quantum
theory and ICBA to do it now, but Martin is normally pretty fussy about
getting the science right, so I'd be surprised if he is wrong here.

I have a little Cree torch here which produces pretty white light. It
has a yellow die, presumably a phosphor triggered by short wavelengths.
It also runs on a single AA cell, including an Eneloop.

Doesn't that mean there must be a voltage multiplier circuit? In which
case the type of battery or its voltage is irrelevent.

On Thu, 29 Dec 2016 16:28:17 +0000, newshound wrote:

Doesn't that mean there must be a voltage multiplier circuit? In which
case the type of battery or its voltage is irrelevent.

The most elementary and cheapest form of voltage multiplier is a ladder-
like network of capacitors and diodes. Can you see anything like that
inside the torch?

newshound wrote:

Doesn't that mean there must be a voltage multiplier circuit? In which
case the type of battery or its voltage is irrelevent.

I think that's quite likely though I don't really know. As you say,
if there's electronics between the battery/cell and the LED then
anything *might* happen with different cell technologies.

--
Chris Green
·

On Thu, 29 Dec 2016 18:16:17 +0000, Gunther Heiko Hagen wrote:

On Thu, 29 Dec 2016 16:28:17 +0000, newshound wrote:

Doesn't that mean there must be a voltage multiplier circuit? In which
case the type of battery or its voltage is irrelevent.

The most elementary and cheapest form of voltage multiplier is a ladder-
like network of capacitors and diodes. Can you see anything like that
inside the torch?

Better look for some sort of oscillator as well; those multipliers won't
run straight off a battery.

On 30/12/16 01:21, Chris wrote:
On Thu, 29 Dec 2016 18:16:17 +0000, Gunther Heiko Hagen wrote:

On Thu, 29 Dec 2016 16:28:17 +0000, newshound wrote:

Doesn't that mean there must be a voltage multiplier circuit? In which
case the type of battery or its voltage is irrelevent.

The most elementary and cheapest form of voltage multiplier is a ladder-
like network of capacitors and diodes. Can you see anything like that
inside the torch?

Better look for some sort of oscillator as well; those multipliers won't
run straight off a battery.

And once you have an oscillator, its a toss up as to which is cheaper -
a chain of diodes and capacitors or a little bit of wound ferrite.

Gunther Heiko Hagen wrote
newshound wrote

Doesn't that mean there must be a voltage multiplier circuit?
In which case the type of battery or its voltage is irrelevent.

The most elementary and cheapest form of voltage multiplier
is a ladder-like network of capacitors and diodes.

Its very far from clear that it is the cheapest anymore.

Can you see anything like that inside the torch?

Bet there is an ic in there.

On Sat, 24 Dec 2016 21:26:15 -0000, Cursitor Doom wrote:

On Sat, 24 Dec 2016 10:01:48 +0000, Brian Gaff wrote:

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.
Brian

Obviously? Why obviously? Most small LEDs turn on at less than one volt

Wrong. More than a volt.

--
TESTICULATING
Waving your arms around and talking ********.

Yes it depends very much on the mode of operation of course.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Rod Speed" wrote in message
...
Brian Gaff wrote

I would suspect they will in most cases, but obviously one might expect
them to be a bit dimmer.

If they have been properly designed so they run the leds at full
intensity even when the alkaline has dropped to below 1V, they
wont be any dimmer with nickel metal hydride rechargeable.


"ss" wrote in message
news
I have a sep of LEDs (xmas lights) Original batteries were Alkaline 1.5V.
Are the LEDs likely to run from 1.2V nickel metal hydride rechargeables?