Reply by three_jeeps ●January 23, 20232023-01-23
On Monday, January 23, 2023 at 5:51:08 AM UTC-5, upsid...@downunder.com wrote:

> On Sun, 22 Jan 2023 16:29:08 -0800 (PST), Three Jeeps 
> <jjhu...@gmail.com> wrote: 
> 
> >For devices that are suppose to last for quite a long time, putting any light emitting devices in series is really stupid - for one of the reasons you point out.
> Due to the temperature coefficient LEDs need to be driven by a 
> constant current source, not by a constant voltage source. 
> 
> If you want to put multiple LEDs in parallel and feed them with a 
> constant voltage, you need to put individual series resistors for each 
> LED, this will limit the individual LED currents. 
> 
> Putting multiple LEDs in series, a single constant current source is 
> enough, like a single series resistor.

Right, I know/understand that.  Different design approaches and those extra resistors amount to perhaps an extra $0.10 which probably adds $2.00+ to the cost of the final product.  Yea gotta produce cheap, cheap, cheap and dupe the unsuspecting public. 

I had a colleague many years ago (late 70's early 80;s) who worked at Zenith Corp designing cks for tv's and other electronic devices.  His assignments typically consisted of:  here is a circuit for a subsection of a TV...reduce parts count.  Sometimes he was given the assignment of developing a new circuit, if his circuit added between $0.04 to 0.05 USD, he went through a 'design review' and in most cases was told to do it over again with no cost increase.   He figures the money he saved went into paying the people that 'handcrafted' the sets....(there is a joke there if you remember those commercials...)
Reply by ●January 23, 20232023-01-23
On Sun, 22 Jan 2023 16:29:08 -0800 (PST), Three Jeeps
<jjhudak4@gmail.com> wrote:


>For devices that are suppose to last for quite a long time, putting any light emitting devices in series is really stupid - for one of the reasons you point out. 


Due to the temperature coefficient LEDs need to be driven by a
constant current source, not by a constant voltage source.

If you want to put multiple LEDs in parallel and feed them with a
constant voltage, you need to put individual series resistors for each
LED, this will limit the individual LED currents.

Putting multiple LEDs in series, a single constant current source is
enough, like a single series resistor.
Reply by Martin Brown ●January 23, 20232023-01-23
On 23/01/2023 00:29, Three Jeeps wrote:

> On Thursday, January 19, 2023 at 10:37:33 AM UTC-5, Martin Brown
> wrote:
>> On 19/01/2023 15:11, albert wrote:
>>> In article <nnd$4d9a769b$61464ae6@e846562bf142425e>, Sjouke Burry
>>> <burrynu...@ppllaanneett.nnll> wrote:
>>>> On 26.12.22 18:16, Ricky wrote:
>>>>> I know it costs more to make a more efficient LED bulb for
>>>>> room
>>>> lighting. Is there also a tradeoff between efficiency and
>>>> operating life? I can't think of a mechanism, but I'm not so
>>>> familiar with LED light bulb design.
>>>>> 
>>>> Lots of light, high chip temp, shorter chip life.
>>> 
>>> This can be offset by operating the leds vastly below capacity. 
>>> E.g. I have a flash light costing 3.5 euro with 37 leds. I
>>> estimate that the leds have an effectively infinite life span. 
>>> Unlike light bulbs you can diminish the current and have
>>> approximately proportional light.
>> The catch is that if they are all in series with a current source
>> or worse rectified mains then the first one to fail takes the
>> entire chain out so MTBF is about 1/N th of the N components in the
>> chain. I have seen some where there were ~60 white leds in series.
>> 
>> Traffic lights seem to have about 4 chains that are independent so
>> you don't get nice even illumination if one fails but they don't
>> just stop completely one day like the old filament bulbs did.
> 
> For devices that are suppose to last for quite a long time, putting
> any light emitting devices in series is really stupid - for one of
> the reasons you point out.  Same issue for the (LED or incandescent)
> Christmas lights.


The old filament ones would be guaranteed not to work out of the box 
every year and require at a minimum tightening all the bulbs in their 
sockets and more likely a binary chop search to find the failed one. 
They also had full mains voltage across the break. Later versions had a 
conductive breakdown glass so that if one bulb failed it would provide a 
current path but no voltage drop so the rest stay lit but brighter. 
There was a fuse lamp to prevent runaway failure if several blew.

Curiously to save wire a lot of the modern LED ones do use long chains 
of LEDS and a common earth. I have a set under my desk from the Village 
Hall awaiting repair at the moment. Half the LEDs on it don't light.


>  A vicious plot to drive the consumers crazy and
> increase profits for the mfg.   I've repaired a few monitors that
> have a LED in series light strip. Sme stupid design.  There are a few
> (2, 3) strips in parallel depending on the size of the monitor but if
> one strip goes out the brightness goes south quickly.


LEDs are pretty reliable compared to filamen bulbs so it isn't all that 
crazy a design. The ones I object to are cheap and nasty Chinese 
rectified mains ones that put ~100 LEDs in series.

-- 
Regards,
Martin Brown
Reply by Lasse Langwadt Christensen ●January 22, 20232023-01-22
mandag den 23. januar 2023 kl. 01.29.12 UTC+1 skrev jjhu...@gmail.com:

> On Thursday, January 19, 2023 at 10:37:33 AM UTC-5, Martin Brown wrote:
> > On 19/01/2023 15:11, albert wrote: 
> > > In article <nnd$4d9a769b$61464ae6@e846562bf142425e>, 
> > > Sjouke Burry <burrynu...@ppllaanneett.nnll> wrote: 
> > >> On 26.12.22 18:16, Ricky wrote: 
> > >>> I know it costs more to make a more efficient LED bulb for room 
> > >> lighting. Is there also a tradeoff between efficiency and operating 
> > >> life? I can't think of a mechanism, but I'm not so familiar with LED 
> > >> light bulb design. 
> > >>> 
> > >> Lots of light, high chip temp, shorter chip life. 
> > > 
> > > This can be offset by operating the leds vastly below capacity. 
> > > E.g. I have a flash light costing 3.5 euro with 37 leds. 
> > > I estimate that the leds have an effectively infinite life span. 
> > > Unlike light bulbs you can diminish the current and have approximately 
> > > proportional light.
> > The catch is that if they are all in series with a current source or 
> > worse rectified mains then the first one to fail takes the entire chain 
> > out so MTBF is about 1/N th of the N components in the chain. I have 
> > seen some where there were ~60 white leds in series. 
> >
> > Traffic lights seem to have about 4 chains that are independent so you 
> > don't get nice even illumination if one fails but they don't just stop 
> > completely one day like the old filament bulbs did. 
> > 
> > -- 
> > Regards, 
> > Martin Brown 
> 
> For devices that are suppose to last for quite a long time, putting any light emitting devices in series is really stupid - for one of the reasons you point out. Same issue for the (LED or incandescent) Christmas lights. A vicious plot to drive the consumers crazy and increase profits for the mfg. I've repaired a few monitors that have a LED in series light strip. Sme stupid design. There are a few (2, 3) strips in parallel depending on the size of the monitor but if one strip goes out the brightness goes south quickly.


if any part of the long filament in a light bulb fails, it goes out and it is scrap ...
Reply by Three Jeeps ●January 22, 20232023-01-22
On Saturday, January 21, 2023 at 6:51:52 AM UTC-5, Martin Brown wrote:

> On 20/01/2023 16:33, Liz Tuddenham wrote: 
> > albert <albert@cherry.(none)> wrote: 
> > 
> > [...] 
> >> The failure modes are dropping from two meters on a concrete flour, 
> >> and the switch. 
> > 
> > ...and leaking batteries.
> Avoid Duracell and you won't have a problem! 
> 
> I prefer Panasonic and Eveready these days - never had on leak. 
> 
> 
> -- 
> Regards, 
> Martin Brown


+1 on avoiding Duracell. I've never seen a battery other than Duracell where both the + and - endcaps separated themselves from the body.   Enloop/Fujitsu or Amazon basic rechargables for the last 5 years for all my devices.  Well there are the flashlights that use 14500.  Never had any of those fail....
Reply by Three Jeeps ●January 22, 20232023-01-22
On Thursday, January 19, 2023 at 10:37:33 AM UTC-5, Martin Brown wrote:

> On 19/01/2023 15:11, albert wrote: 
> > In article <nnd$4d9a769b$61464ae6@e846562bf142425e>, 
> > Sjouke Burry <burrynu...@ppllaanneett.nnll> wrote: 
> >> On 26.12.22 18:16, Ricky wrote: 
> >>> I know it costs more to make a more efficient LED bulb for room 
> >> lighting. Is there also a tradeoff between efficiency and operating 
> >> life? I can't think of a mechanism, but I'm not so familiar with LED 
> >> light bulb design. 
> >>> 
> >> Lots of light, high chip temp, shorter chip life. 
> > 
> > This can be offset by operating the leds vastly below capacity. 
> > E.g. I have a flash light costing 3.5 euro with 37 leds. 
> > I estimate that the leds have an effectively infinite life span. 
> > Unlike light bulbs you can diminish the current and have approximately 
> > proportional light.
> The catch is that if they are all in series with a current source or 
> worse rectified mains then the first one to fail takes the entire chain 
> out so MTBF is about 1/N th of the N components in the chain. I have 
> seen some where there were ~60 white leds in series. 
> 
> Traffic lights seem to have about 4 chains that are independent so you 
> don't get nice even illumination if one fails but they don't just stop 
> completely one day like the old filament bulbs did. 
> 
> -- 
> Regards, 
> Martin Brown


For devices that are suppose to last for quite a long time, putting any light emitting devices in series is really stupid - for one of the reasons you point out.  Same issue for the (LED or incandescent) Christmas lights.  A vicious plot to drive the consumers crazy and increase profits for the mfg.   I've repaired a few monitors that have a LED in series light strip. Sme stupid design.  There are a few (2, 3) strips in parallel depending on the size of the monitor but if one strip goes out the brightness goes south quickly.
Reply by Phil Hobbs ●January 22, 20232023-01-22
Martin Brown wrote:

> On 21/01/2023 22:33, Phil Hobbs wrote:
>> Martin Brown wrote:
>>> On 20/01/2023 22:18, Phil Hobbs wrote:
>>>> upsidedown@downunder.com wrote:
>>>>> On Thu, 19 Jan 2023 16:11:35 +0100, albert@cherry.(none) (albert)
>>>>> wrote:
>>>>>
>>>>>> In article <nnd$4d9a769b$61464ae6@e846562bf142425e>,
>>>>>> Sjouke Burry&nbsp; <burrynulnulfour@ppllaanneett.nnll> wrote:
>>>>>>> On 26.12.22 18:16, Ricky wrote:
>>>>>>>> I know it costs more to make a more efficient LED bulb for room
>>>>>>> lighting.&nbsp; Is there also a tradeoff between efficiency and operating
>>>>>>> life?&nbsp; I can't think of a mechanism, but I'm not so familiar with 
>>>>>>> LED
>>>>>>> light bulb design.
>>>>>>>>
>>>>>>> Lots of light, high chip temp, shorter chip life.
>>>>>>
>>>>>> This can be offset by operating the leds vastly below capacity.
>>>>>> E.g. I have a flash light costing 3.5 euro with 37 leds.
>>>>>> I estimate that the leds have an effectively infinite life span.
>>>>>> Unlike light bulbs you can diminish the current and have 
>>>>>> approximately
>>>>>> proportional light.
>>>>>>
>>>>>> Groetjes Albert
>>>>>
>>>>>
>>>>> The problem with 'white' LEDs is the degradation of the phosphor with
>>>>> high currents. Running the LED at Imax and the light output will drop
>>>>> significantly after a few hundred or a thousand hours. Running at
>>>>> Imax/2 or even Imax/3 and the light output may be strong after claimed
>>>>> 30000 hours. The efficiency (in lm/W) is also&nbsp; better for the lower
>>>>> current.
>>>>>
>>>>> Reputable LED manufacturers specify the light characteristics well
>>>>> below maximum allowed Imax current, often at Imax/2 or Imax/3 so with
>>>>> IMax=1 A, the characteristics are specified at 350 mA.
>>>>>
>>>>> Of course, this requires two or three times the number of LEDs to get
>>>>> the same light output and hence the lamp is more expensive, but this
>>>>> extends the usable life time with more than 3 times, thus being more
>>>>> economical in the long run.
>>>>
>>>> If the phosphor were responsible, you'd expect the light output to 
>>>> get bluer and bluer as the lamp aged, which I don't think it does.
>>>
>>> I think it is the organic binder or glue that holds it all together 
>>> that degrades to become darker with free carbon in it under the 
>>> influence of such a high light flux.
>>
>> Still you'd expect a fairly large colour shift, which I don't think is 
>> observed.
> 
> It is the blue LED to phosphor interface degrading under the flux of 
> blue photons so I'd expect comparatively little colour shift if the 
> intensity of blue light reaching the phosphor is reduced by being 
> absorbed by carbon black particles before it gets there.
> 
> Organic materials don't really get on with shorter wavelengths.
> 


I'm not at all sure that charring is the mechanism, though.  Usually 
polymer binders turn a dirty yellow, not grey.

Cheers

Phil Hobbs

-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
Reply by Martin Brown ●January 22, 20232023-01-22
On 21/01/2023 22:33, Phil Hobbs wrote:

> Martin Brown wrote:
>> On 20/01/2023 22:18, Phil Hobbs wrote:
>>> upsidedown@downunder.com wrote:
>>>> On Thu, 19 Jan 2023 16:11:35 +0100, albert@cherry.(none) (albert)
>>>> wrote:
>>>>
>>>>> In article <nnd$4d9a769b$61464ae6@e846562bf142425e>,
>>>>> Sjouke Burry&nbsp; <burrynulnulfour@ppllaanneett.nnll> wrote:
>>>>>> On 26.12.22 18:16, Ricky wrote:
>>>>>>> I know it costs more to make a more efficient LED bulb for room
>>>>>> lighting.&nbsp; Is there also a tradeoff between efficiency and operating
>>>>>> life?&nbsp; I can't think of a mechanism, but I'm not so familiar with LED
>>>>>> light bulb design.
>>>>>>>
>>>>>> Lots of light, high chip temp, shorter chip life.
>>>>>
>>>>> This can be offset by operating the leds vastly below capacity.
>>>>> E.g. I have a flash light costing 3.5 euro with 37 leds.
>>>>> I estimate that the leds have an effectively infinite life span.
>>>>> Unlike light bulbs you can diminish the current and have approximately
>>>>> proportional light.
>>>>>
>>>>> Groetjes Albert
>>>>
>>>>
>>>> The problem with 'white' LEDs is the degradation of the phosphor with
>>>> high currents. Running the LED at Imax and the light output will drop
>>>> significantly after a few hundred or a thousand hours. Running at
>>>> Imax/2 or even Imax/3 and the light output may be strong after claimed
>>>> 30000 hours. The efficiency (in lm/W) is also&nbsp; better for the lower
>>>> current.
>>>>
>>>> Reputable LED manufacturers specify the light characteristics well
>>>> below maximum allowed Imax current, often at Imax/2 or Imax/3 so with
>>>> IMax=1 A, the characteristics are specified at 350 mA.
>>>>
>>>> Of course, this requires two or three times the number of LEDs to get
>>>> the same light output and hence the lamp is more expensive, but this
>>>> extends the usable life time with more than 3 times, thus being more
>>>> economical in the long run.
>>>
>>> If the phosphor were responsible, you'd expect the light output to 
>>> get bluer and bluer as the lamp aged, which I don't think it does.
>>
>> I think it is the organic binder or glue that holds it all together 
>> that degrades to become darker with free carbon in it under the 
>> influence of such a high light flux.
> 
> Still you'd expect a fairly large colour shift, which I don't think is 
> observed.


It is the blue LED to phosphor interface degrading under the flux of 
blue photons so I'd expect comparatively little colour shift if the 
intensity of blue light reaching the phosphor is reduced by being 
absorbed by carbon black particles before it gets there.

Organic materials don't really get on with shorter wavelengths.

-- 
Regards,
Martin Brown
Reply by Phil Hobbs ●January 21, 20232023-01-21
Martin Brown wrote:

> On 20/01/2023 22:18, Phil Hobbs wrote:
>> upsidedown@downunder.com wrote:
>>> On Thu, 19 Jan 2023 16:11:35 +0100, albert@cherry.(none) (albert)
>>> wrote:
>>>
>>>> In article <nnd$4d9a769b$61464ae6@e846562bf142425e>,
>>>> Sjouke Burry&nbsp; <burrynulnulfour@ppllaanneett.nnll> wrote:
>>>>> On 26.12.22 18:16, Ricky wrote:
>>>>>> I know it costs more to make a more efficient LED bulb for room
>>>>> lighting.&nbsp; Is there also a tradeoff between efficiency and operating
>>>>> life?&nbsp; I can't think of a mechanism, but I'm not so familiar with LED
>>>>> light bulb design.
>>>>>>
>>>>> Lots of light, high chip temp, shorter chip life.
>>>>
>>>> This can be offset by operating the leds vastly below capacity.
>>>> E.g. I have a flash light costing 3.5 euro with 37 leds.
>>>> I estimate that the leds have an effectively infinite life span.
>>>> Unlike light bulbs you can diminish the current and have approximately
>>>> proportional light.
>>>>
>>>> Groetjes Albert
>>>
>>>
>>> The problem with 'white' LEDs is the degradation of the phosphor with
>>> high currents. Running the LED at Imax and the light output will drop
>>> significantly after a few hundred or a thousand hours. Running at
>>> Imax/2 or even Imax/3 and the light output may be strong after claimed
>>> 30000 hours. The efficiency (in lm/W) is also&nbsp; better for the lower
>>> current.
>>>
>>> Reputable LED manufacturers specify the light characteristics well
>>> below maximum allowed Imax current, often at Imax/2 or Imax/3 so with
>>> IMax=1 A, the characteristics are specified at 350 mA.
>>>
>>> Of course, this requires two or three times the number of LEDs to get
>>> the same light output and hence the lamp is more expensive, but this
>>> extends the usable life time with more than 3 times, thus being more
>>> economical in the long run.
>>
>> If the phosphor were responsible, you'd expect the light output to get 
>> bluer and bluer as the lamp aged, which I don't think it does.
> 
> I think it is the organic binder or glue that holds it all together that 
> degrades to become darker with free carbon in it under the influence of 
> such a high light flux.


Still you'd expect a fairly large colour shift, which I don't think is 
observed.


>>
>> The phosphor/fluor is inorganic, so it doesn't degrade the way organic 
>> dyes do.
> 
> Moisture ingress appears to be the main mechanism by which the high 
> intensity ones degrade in the wild. The harder you run them the worse it 
> gets with differential thermal expansion. eg.
> 
> https://www.nature.com/articles/srep24052


Interesting, thanks.

Cheers

Phil Hobbs



-- 
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
Reply by John Larkin ●January 21, 20232023-01-21
On Sat, 21 Jan 2023 11:51:41 +0000, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:


>On 20/01/2023 14:05, albert wrote:
>> In article <tqbo3l$1rk6$1@gioia.aioe.org>,
>> Martin Brown  <'''newspam'''@nonad.co.uk> wrote:
>>> On 19/01/2023 15:11, albert wrote:
>>>> In article <nnd$4d9a769b$61464ae6@e846562bf142425e>,
>>>> Sjouke Burry  <burrynulnulfour@ppllaanneett.nnll> wrote:
>>>>> On 26.12.22 18:16, Ricky wrote:
>>>>>> I know it costs more to make a more efficient LED bulb for room
>>>>> lighting.  Is there also a tradeoff between efficiency and operating
>>>>> life?  I can't think of a mechanism, but I'm not so familiar with LED
>>>>> light bulb design.
>>>>>>
>>>>> Lots of light, high chip temp, shorter chip life.
>>>>
>>>> This can be offset by operating the leds vastly below capacity.
>>>> E.g. I have a flash light costing 3.5 euro with 37 leds.
>>>> I estimate that the leds have an effectively infinite life span.
>>>> Unlike light bulbs you can diminish the current and have approximately
>>>> proportional light.
>>>
>>> The catch is that if they are all in series with a current source or
>>> worse rectified mains then the first one to fail takes the entire chain
>>> out so MTBF is about 1/N th of the N components in the chain. I have
>>> seen some where there were ~60 white leds in series.
>> 
>> That is true in mains application. A pocket light working from
>> 3 AA's have the leds in parallel. There is a series resistor,
>> possibly to a group of leds.
>




>It is quite rare now to find that 3 AA's & resistor configuration. Most 
>have either a single AA cell or a pair of them and a voltage to current 
>converter that drives the stack (or a single one) at constant current.


The little key-ring LED things often have one cell, one LED, no
resistor.