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What current is drawn by LED mains night light?

P

Peter

Jan 1, 1970
0
How much current is drawn by an LED night light which runs off the
mains?

BTW what sort of circuit is used for a LED to run off the mains. Is
it just a drop down resistor and a rectifier?
 
J

Joerg

Jan 1, 1970
0
J

Jon Kirwan

Jan 1, 1970
0

The author there makes an interesting comment.

"... after only three months, the light gradually faded until it was
virtually useless. This has happened to me several times before with
other lights I have tried and results from the use of cheap inferior
white LEDs, which have phosphors that quickly fade."

I had no idea people were using phosphors that would be significantly
damaged by blue LED emissions. I am trying to understand exactly how
that would happen, besides. So I guess the author must mean that the
phosphors are simply chemically unstable to begin with.

Does anyone happen to know precisely which phosphor material is being
used in these "cheap inferior white LEDs," as the author wrote? I'd
like to know.

Jon
 
M

Martin Brown

Jan 1, 1970
0
Jon said:
The author there makes an interesting comment.

"... after only three months, the light gradually faded until it was
virtually useless. This has happened to me several times before with
other lights I have tried and results from the use of cheap inferior
white LEDs, which have phosphors that quickly fade."

I suppose it depends how cheap and nasty your white LED supplier is. I
have had a white LED based night light running for best part of 5 years
and the amazing thing is that the minimum current required for a dark
adapted eye to see by is around 10uA. So in principle you could just run
a night lite off a capacitive divider and rectifier with a suitable
choke/resistor in series to protect the diode from any nasty transients
that come down the line. Power used by that at 3mW would be hard for a
normal mains electricity meter to detect.

Mine uses a 9v rechargable that lasts about a year in its standby state
- it will run as a torch if switched on. But it is never quite off which
makes the torch a lot easier to find if the power drops after dark.
I had no idea people were using phosphors that would be significantly
damaged by blue LED emissions. I am trying to understand exactly how
that would happen, besides. So I guess the author must mean that the
phosphors are simply chemically unstable to begin with.

Does anyone happen to know precisely which phosphor material is being
used in these "cheap inferior white LEDs," as the author wrote? I'd
like to know.

It is a surprising claim. I expect there are some yellow organic dyes or
pigments like rubrene that do degrade fairly quickly under the influence
of blue to near UV light. But I'd be very surprised if the normal
inorganic phosphors of white LEDs ever failed in that way.

Question now is which brands of white LED are using unstable phosphors
(if any).

Regards,
Martin Brown
 
J

Joerg

Jan 1, 1970
0
Jan said:
I have one, it says 1W.
Pretty bright though, it says 'Deco LED', and is made by Philips,
maybe not really a night light.


No, I think it could be some switcher.


Hold an AM radio next to it, then you'll know.

[...]
 
J

Joerg

Jan 1, 1970
0
Jon said:
The author there makes an interesting comment.

"... after only three months, the light gradually faded until it was
virtually useless. This has happened to me several times before with
other lights I have tried and results from the use of cheap inferior
white LEDs, which have phosphors that quickly fade."

I had no idea people were using phosphors that would be significantly
damaged by blue LED emissions. I am trying to understand exactly how
that would happen, besides. So I guess the author must mean that the
phosphors are simply chemically unstable to begin with.

Does anyone happen to know precisely which phosphor material is being
used in these "cheap inferior white LEDs," as the author wrote? I'd
like to know.

John Larkin once said that everything electronic that emits something
such as light doesn't live forever. On every project I was involved in
with serious LEDs on there lifetime was one of the agenda items to discuss.

I assume it's like with CFL. Our first round died within the year, well
short of their 10x light bulb claims. So I gave up on this technology
for many years. Then I tried again, this time Philips Marathon. They
seem to last forever.
 
R

Rich Grise

Jan 1, 1970
0
I assume it's like with CFL. Our first round died within the year, well
short of their 10x light bulb claims. So I gave up on this technology
for many years. Then I tried again, this time Philips Marathon. They
seem to last forever.

I saw one of those whiny "green" shows on "edjamacational" TeeVee, and
they said, "Don't throw incandescents in the trash. The glass takes
hundreds of years to break down."

What a bunch of idiots. Glass is ALREADY DIRT!!

Cheers!
Rich
 
J

Joerg

Jan 1, 1970
0
John said:
They should still emit a bunch of blue.


I bought a bunch of cool blue led night lights, a year or so ago, and
set one aside as a reference to check against once in a while. No
visible diff so far. Must have got lucky.

Blue for a night light? Yuck.

Neons usually last a few years. ELs fade and do other weird things.

We still use the little incandescent ones. They last several years and
have a nice spectrum.

If they're left on all the time, they last a lot more than if they're
cycled. 7 watts isn't a lot of power to leave on.

I think they have 14W or so. But they are way too bright as a night
light. Also, these don't seem to mind cycling and their brightness is
usable right after turn-on (except in winter). The CFL flood light
outdoors, different thing. Easily takes a minute to get from near-IR to
white. Or several minutes in winter.
 
J

Jon Kirwan

Jan 1, 1970
0
John Larkin once said that everything electronic that emits something
such as light doesn't live forever. On every project I was involved in
with serious LEDs on there lifetime was one of the agenda items to discuss.

I assume it's like with CFL. Our first round died within the year, well
short of their 10x light bulb claims. So I gave up on this technology
for many years. Then I tried again, this time Philips Marathon. They
seem to last forever.

Well, I didn't want to be as vague as all that. I work with rare
earth phosphors, regularly. And they are pretty hardy materials,
fired usually at highish temperatures and not prone to changing
structure by the fly-speck energies found in near-400nm photon. I
mean, this is only 3eV or so. Most I've worked with are fine at 5eV
almost forever.

I find Martin's response just about exactly how I feel about it. There
are organic/laser dyes that do degrade. But these aren't what I
thought they were using in white LEDs. As he points out in what I
consider to be broad agreement with me, rare earth ceramic/inorganic
phosphors pretty much just work all day long.

I think the LED itself can indeed fail. But not the phosphor. That's
hard for me to imagine, right now. In the case you talk about with
CFLs, I've opened up just about every CFL that has ever failed in my
home and taken a close look -- dismantling every single part, in fact.
There is a particular brand I find to have very dangerous designs (it
is sold at Costco) and those burn up for just about every imaginable
reason. I've had capacitors explode and burn, transistors literally
blow their sides out, inductors which overheated and caught fire, etc.
I think they under-design the entire thing. It's all at risk. On the
other hand, as you say, the Marathon units are much better designed.
hehe. In fact, they also use a more complex method to actually attach
the circuit board between the screw end and the bulb that makes it
harder for me to gain access, too. But when they fail, it seems to be
that the parts do NOT burn up. (I've only had two fail so far from
them and I think both cases related to the fluorescent bulb itself --
but NOT the failure of its phosphor material.)

Jon
 
J

Jon Kirwan

Jan 1, 1970
0
Jan said:
I have one, it says 1W.
Pretty bright though, it says 'Deco LED', and is made by Philips,
maybe not really a night light.


No, I think it could be some switcher.

Hold an AM radio next to it, then you'll know.

[...]

Now that's how I used to "listen" to my software operating on the
Altair 8800! Wonderful way to detect loops, etc.

Jon
 
J

Joerg

Jan 1, 1970
0
Jon said:
Well, I didn't want to be as vague as all that. I work with rare
earth phosphors, regularly. And they are pretty hardy materials,
fired usually at highish temperatures and not prone to changing
structure by the fly-speck energies found in near-400nm photon. I
mean, this is only 3eV or so. Most I've worked with are fine at 5eV
almost forever.

I find Martin's response just about exactly how I feel about it. There
are organic/laser dyes that do degrade. But these aren't what I
thought they were using in white LEDs. As he points out in what I
consider to be broad agreement with me, rare earth ceramic/inorganic
phosphors pretty much just work all day long.

I think the LED itself can indeed fail. But not the phosphor. That's
hard for me to imagine, right now. In the case you talk about with
CFLs, I've opened up just about every CFL that has ever failed in my
home and taken a close look -- dismantling every single part, in fact.
There is a particular brand I find to have very dangerous designs (it
is sold at Costco) and those burn up for just about every imaginable
reason. I've had capacitors explode and burn, transistors literally
blow their sides out, inductors which overheated and caught fire, etc.
I think they under-design the entire thing. It's all at risk. On the
other hand, as you say, the Marathon units are much better designed.


I actually bought those at Costco, at the time when a utility/state
subsidy made them irresistably cheap. A Dollar a piece.

hehe. In fact, they also use a more complex method to actually attach
the circuit board between the screw end and the bulb that makes it
harder for me to gain access, too. But when they fail, it seems to be
that the parts do NOT burn up. (I've only had two fail so far from
them and I think both cases related to the fluorescent bulb itself --
but NOT the failure of its phosphor material.)

The ones from the previous run failed rather quietly. Sometimes I also
suspected the electronics but some had a distinctively blackened
fluorescent coil. Those were the ones that didn't fail point-blank but
would have a harder and harder time to start, or would only start on
warmer days.
 
J

Joerg

Jan 1, 1970
0
Jon said:
Jan said:
On a sunny day (Wed, 23 Sep 2009 21:06:53 +0100) it happened Peter
<[email protected]>:

How much current is drawn by an LED night light which runs off the
mains?
I have one, it says 1W.
Pretty bright though, it says 'Deco LED', and is made by Philips,
maybe not really a night light.

BTW what sort of circuit is used for a LED to run off the mains. Is
it just a drop down resistor and a rectifier?
No, I think it could be some switcher.
Hold an AM radio next to it, then you'll know.

[...]

Now that's how I used to "listen" to my software operating on the
Altair 8800! Wonderful way to detect loops, etc.

We did that on programmable pocket calculators. When the warbling and
chirping changed to an even buzz that meant the routine had finished :)
 
O

oopere

Jan 1, 1970
0
linnix said:
I am not saying this is the proper way to do it. Don't sue me if
someone get shocked. A single 100K resistor will light up an LED at
10mA. LED is a diode.

Better(*) two LEDs in antiparallel. Reverse voltage in the 'off' state
fries a single LED.

(*) Of course, there are even better ways :)

Pere
 
M

Martin Brown

Jan 1, 1970
0
John said:
They should still emit a bunch of blue.

Blue looks subjectively a lot dimmer to the eye even though the photon
energy is higher. But having said that I suspect what causes the LEDs in
this circuit to fade is damage inflicted by fast mains transients and
inductive spikes on the mains.

Compared to incandescent filament bulbs they are fabulously reliable -
and in many modern display applications have excellent collimation built
in. Signs on motorways that are highly visible from a long way off but
do not dazzle nearby drivers are one major application.
I bought a bunch of cool blue led night lights, a year or so ago, and
set one aside as a reference to check against once in a while. No
visible diff so far. Must have got lucky.

Neons usually last a few years. ELs fade and do other weird things.

I can't recall ever seeing a neon indicator that has failed without
being smashed. I have some lying around from decades ago that still
work. Laser tubes seem to expire more easily.
If they're left on all the time, they last a lot more than if they're
cycled. 7 watts isn't a lot of power to leave on.

Depends how many lots of 7W you have left on.

Regards,
Martin Brown
 
R

Rich Grise

Jan 1, 1970
0
Speaking of fading lights, I have a Totaline automatic switchover thermostat
in my home. IIRC, it uses an EL backlit display but it no longer
backlights. It used to be quite bright; the backlighting was very visible
even with room lights on. Now, after about 5 years, the backlighting is
totally gone. I can still read the display, but the room lights have to be
on.
Wondering... would an LED restore the backlighting? Where would it need to
be positioned... directly behind the display or to the side?

The optimum, of course, would be to replace the EL with OEM, if it can
still be had. As far as using an LED, that depends on a lot of factors,
like how much room you have, form factor, and so on.

Good Luck!
Rich
 
J

Joerg

Jan 1, 1970
0
Jan said:
I just held the scope probe next to it.
I cannot uniquely identify any switcher RF, lots of other RF though.
Some sawtooth like waveform of few kHz near the the bulb... mV
So tried the radio, MW 580 kHz or so.
Indeed when switching on there is a strong noise, for about half a second,
then a sort of white noise stays, much whiter then the other interference crap.
Switcher?

Maybe a "loose cannon" switcher? One old trick is (or in some markets
was) to dither its frequency so you can fly under the EMC radar screens,
get away with much in shields and ferrites.
 
E

E

Jan 1, 1970
0
Jon Kirwan said:
The author there makes an interesting comment.

"... after only three months, the light gradually faded until it was
virtually useless. This has happened to me several times before with
other lights I have tried and results from the use of cheap inferior
white LEDs, which have phosphors that quickly fade."

I had no idea people were using phosphors that would be significantly
damaged by blue LED emissions. I am trying to understand exactly how
that would happen, besides. So I guess the author must mean that the
phosphors are simply chemically unstable to begin with.

Does anyone happen to know precisely which phosphor material is being
used in these "cheap inferior white LEDs," as the author wrote? I'd
like to know.

Jon



There is a thread on CPF where someone dissected and photographed
failed chinese led under microscope. Photos show that phospors (or epoxy)
apparently turns black near die

Link:
http://www.candlepowerforums.com/vb/showthread.php?t=128801
Lots of nice microscope photos. Look especially at pages 1 and 6 onwards.

-ek
 
D

Don Klipstein

Jan 1, 1970
0
Well, I didn't want to be as vague as all that. I work with rare
earth phosphors, regularly. And they are pretty hardy materials,
fired usually at highish temperatures and not prone to changing
structure by the fly-speck energies found in near-400nm photon. I
mean, this is only 3eV or so. Most I've worked with are fine at 5eV
almost forever.

I find Martin's response just about exactly how I feel about it. There
are organic/laser dyes that do degrade. But these aren't what I
thought they were using in white LEDs. As he points out in what I
consider to be broad agreement with me, rare earth ceramic/inorganic
phosphors pretty much just work all day long.

I think the LED itself can indeed fail. But not the phosphor. That's
hard for me to imagine, right now.

<SNIP failures other than of phosphors>

Believe me, the inorganic phosphors do degrade in LEDs from photons of
energies 3 eV or a bit less.

Part of the problem may be contamination from other ingredients in the
LED.

Light intensity of tens of watts per square centimeter, a couple orders
of magnitude more intense than in fluorescent lamps (where phosphor life
is usually only 10,000's of hours also), is almost certainly part of
this issue.

- Don Klipstein ([email protected])
 
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