LEDs and Persistent Phosphors...

[Fred Bloggs]

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

 

[Phil Hobbs]

Fred Bloggs <bloggs.fredbloggs.fred@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of
physics and chemistry involved. I\'m not sure where they\'re getting AC LED
operation promises greater efficiency, reliability, and cost savings,
than the DC operation, but people in the industry have reached this
conclusion. AC operation has the drawback of flicker, fluctuating
intensity, which is now recognized as a health hazard, so it must be
reduced/eliminated. Was just scoping out a small mains powered bulb, and
it definitely exhibited an afterglow of a full 45 seconds after power was
removed, not uniform across a bulb population, but close enough. It is
definitely using persistent phosphors. Needless to say one would need a
laboratory grade high sensitivity instrument to detect any flicker.

That’s a huge non sequitur. Optical crapola from switchers driving LEDs
and fluorescents is a plague.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Cheers

Phil Hobbs

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

 

[Piglet]

On 12/09/2023 12:58, Fred Bloggs wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Did you switch off at the AC mains or interrupt the feed directly to the
LEDs - in other words is the afterglow from phosphors or internal
capacitor discharge or maybe even both?

piglet

 

[John Larkin]

On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Another terrifying health hazard!

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around
5 ns resolution.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker
will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.

 

[Jan Panteltje]

On a sunny day (Tue, 12 Sep 2023 07:05:48 -0700) it happened John Larkin
<jjlarkin@highlandtechnology.com> wrote in
<78r0git8l1kh3kt9qafrsvd82i0vkv3k8j@4ax.com>:

On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where
they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in
the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now
recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely
exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is
definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect
any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Another terrifying health hazard!

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around
5 ns resolution.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker
will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.

I think my monitor has a LED backlight, it changes brightness all the time
when working.
Same for my laptop.
But I did switch off the auto brightness feature in the laptop,
annoying changing all the time.
And my room LED lighting is in fact PWM controlled:
https://panteltje.nl/panteltje/pic/ethernet_color_pic/

Some LED lights have no converter chip but run directly from AC,
https://panteltje.nl/pub/LED_light_circuit_diagram_IMG_6925.JPG
the capacitor on the left limits the current
So any current spike will cause a flash.. and kill the LED as in my case.
So avoid that type.
https://panteltje.nl/pub/LED_light_fix_IMG_6918.JPG

 

[Fred Bloggs]

On Tuesday, September 12, 2023 at 9:15:05 AM UTC-4, Piglet wrote:

On 12/09/2023 12:58, Fred Bloggs wrote:
A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in the industry have reached this conclusion.. AC operation has the drawback of flicker, fluctuating intensity, which is now recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979
Did you switch off at the AC mains or interrupt the feed directly to the
LEDs - in other words is the afterglow from phosphors or internal
capacitor discharge or maybe even both?

Turned off the mains with a standard mains toggle switch. The bulb is one those miniature candelabra types, clear, E26 base, no simulated flame or anything like that, GE or something. Hard to imagine it has anything like a storage cap in it. The afterglow was white for about 10 seconds, then turned color to cherry red for remaining 35 seconds.

piglet

 

[Fred Bloggs]

On Tuesday, September 12, 2023 at 10:06:06 AM UTC-4, John Larkin wrote:

On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979
Another terrifying health hazard!

Powers that be could be transmitting power line signals used to control you..

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around
5 ns resolution.

There are landscape pebbles, look like ordinary pebbles, treated with something that is charged by sunlight during the daytime and then emit light in the dark. Used for lighting pathways at night, or aquariums. Same technology is used in paving stones for same purpose. They\'re not real expensive, but definitely not cheap for the application.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker
will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.

There\'s some human optical-brain reaction referred to as \'vibration\'- creates a sensation of more or less blinding vibration in your visual perception.. Looking at a starkly contrasting gingham pattern in ordinary light level, the vibration makes it appear blindingly bright, so much so that you need to turn away or put on sunglasses.

 

[Fred Bloggs]

On Tuesday, September 12, 2023 at 11:12:14 AM UTC-4, Jan Panteltje wrote:

On a sunny day (Tue, 12 Sep 2023 07:05:48 -0700) it happened John Larkin
jjla...@highlandtechnology.com> wrote in
78r0git8l1kh3kt9q...@4ax.com>:
On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where
they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in
the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now
recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely
exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is
definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect
any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Another terrifying health hazard!

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around
5 ns resolution.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker
will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.
I think my monitor has a LED backlight, it changes brightness all the time
when working.
Same for my laptop.
But I did switch off the auto brightness feature in the laptop,
annoying changing all the time.
And my room LED lighting is in fact PWM controlled:
https://panteltje.nl/panteltje/pic/ethernet_color_pic/

Some of these high end light fixtures that program intensity and color temperature of the light source are ridiculously expensive.

Some LED lights have no converter chip but run directly from AC,
https://panteltje.nl/pub/LED_light_circuit_diagram_IMG_6925.JPG
the capacitor on the left limits the current
So any current spike will cause a flash.. and kill the LED as in my case.
So avoid that type.
https://panteltje.nl/pub/LED_light_fix_IMG_6918.JPG

Except for the susceptibility to being destroyed, that looks like a pretty good circuit.

 

[Fred Bloggs]

On Tuesday, September 12, 2023 at 11:12:14 AM UTC-4, Jan Panteltje wrote:

On a sunny day (Tue, 12 Sep 2023 07:05:48 -0700) it happened John Larkin
jjla...@highlandtechnology.com> wrote in
78r0git8l1kh3kt9q...@4ax.com>:
On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where
they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in
the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now
recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely
exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is
definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect
any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Another terrifying health hazard!

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around
5 ns resolution.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker
will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.
I think my monitor has a LED backlight, it changes brightness all the time
when working.
Same for my laptop.
But I did switch off the auto brightness feature in the laptop,
annoying changing all the time.
And my room LED lighting is in fact PWM controlled:
https://panteltje.nl/panteltje/pic/ethernet_color_pic/

Some LED lights have no converter chip but run directly from AC,
https://panteltje.nl/pub/LED_light_circuit_diagram_IMG_6925.JPG
the capacitor on the left limits the current
So any current spike will cause a flash.. and kill the LED as in my case.
So avoid that type.
https://panteltje.nl/pub/LED_light_fix_IMG_6918.JPG

This Chinese special looks a little more robust:

https://ledask.com/ezoimgfmt/www.ourpcb.com/wp-content/uploads/2021/08/QQ%E6%88%AA%E5%9B%BE20210819113943.jpg

Almost incoherent write-up here:

https://ledask.com/led-bulb-circuit/

No wonder their crummy bulbs flicker.

 

[John Larkin]

On Tue, 12 Sep 2023 08:54:55 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Tuesday, September 12, 2023 at 10:06:06?AM UTC-4, John Larkin wrote:
On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot of physics and chemistry involved. I\'m not sure where they\'re getting AC LED operation promises greater efficiency, reliability, and cost savings, than the DC operation, but people in the industry have reached this conclusion. AC operation has the drawback of flicker, fluctuating intensity, which is now recognized as a health hazard, so it must be reduced/eliminated. Was just scoping out a small mains powered bulb, and it definitely exhibited an afterglow of a full 45 seconds after power was removed, not uniform across a bulb population, but close enough. It is definitely using persistent phosphors. Needless to say one would need a laboratory grade high sensitivity instrument to detect any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979
Another terrifying health hazard!

Powers that be could be transmitting power line signals used to control you.


It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around
5 ns resolution.

There are landscape pebbles, look like ordinary pebbles, treated with something that is charged by sunlight during the daytime and then emit light in the dark. Used for lighting pathways at night, or aquariums. Same technology is used in paving stones for same purpose. They\'re not real expensive, but definitely not cheap for the application.

Strontium aluminate is fabulous, way way better than the old zinc
sulfide stuff.

 

[Jan Panteltje]

On a sunny day (Tue, 12 Sep 2023 09:42:06 -0700 (PDT)) it happened Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote in
<22db2f57-f72d-4cfb-a208-8d6d7aa7d055n@googlegroups.com>:

On Tuesday, September 12, 2023 at 11:12:14 AM UTC-4, Jan Panteltje =
wrote:
On a sunny day (Tue, 12 Sep 2023 07:05:48 -0700) it happened John Larkin=

jjla...@highlandtechnology.com> wrote in
78r0git8l1kh3kt9q...@4ax.com>:
On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot =
of physics and chemistry involved. I\'m not sure where
they\'re getting AC LED operation promises greater efficiency, reliabili=
ty, and cost savings, than the DC operation, but people in
the industry have reached this conclusion. AC operation has the drawbac=
k of flicker, fluctuating intensity, which is now
recognized as a health hazard, so it must be reduced/eliminated. Was ju=
st scoping out a small mains powered bulb, and it definitely
exhibited an afterglow of a full 45 seconds after power was removed, no=
t uniform across a bulb population, but close enough. It is
definitely using persistent phosphors. Needless to say one would need a=
laboratory grade high sensitivity instrument to detect
any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Another terrifying health hazard!

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around=

5 ns resolution.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker=

will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.
I think my monitor has a LED backlight, it changes brightness all the tim=
e
when working.
Same for my laptop.
But I did switch off the auto brightness feature in the laptop,
annoying changing all the time.
And my room LED lighting is in fact PWM controlled:
https://panteltje.nl/panteltje/pic/ethernet_color_pic/

Some LED lights have no converter chip but run directly from AC,
https://panteltje.nl/pub/LED_light_circuit_diagram_IMG_6925.JPG
the capacitor on the left limits the current
So any current spike will cause a flash.. and kill the LED as in my case.=

So avoid that type.
https://panteltje.nl/pub/LED_light_fix_IMG_6918.JPG

This Chinese special looks a little more robust:

https://ledask.com/ezoimgfmt/www.ourpcb.com/wp-content/uploads/2021/08/QQ%E6%88%AA%E5%9B%BE20210819113943.jpg

Yes, adding the electrolytics and R2 R3 should remove most mains surges.
My model from China had none....

Almost incoherent write-up here:

https://ledask.com/led-bulb-circuit/

Yes

No wonder their crummy bulbs flicker.

 

[Jan Panteltje]

On a sunny day (Tue, 12 Sep 2023 09:00:16 -0700 (PDT)) it happened Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote in
<ffc7e88d-e230-412b-bdc7-deed60850abcn@googlegroups.com>:

On Tuesday, September 12, 2023 at 11:12:14 AM UTC-4, Jan Panteltje =
wrote:
On a sunny day (Tue, 12 Sep 2023 07:05:48 -0700) it happened John Larkin=

jjla...@highlandtechnology.com> wrote in
78r0git8l1kh3kt9q...@4ax.com>:
On Tue, 12 Sep 2023 04:58:12 -0700 (PDT), Fred Bloggs
bloggs.fred...@gmail.com> wrote:

A LED is not just a light emitting semi junction, there is quite a lot =
of physics and chemistry involved. I\'m not sure where
they\'re getting AC LED operation promises greater efficiency, reliabili=
ty, and cost savings, than the DC operation, but people in
the industry have reached this conclusion. AC operation has the drawbac=
k of flicker, fluctuating intensity, which is now
recognized as a health hazard, so it must be reduced/eliminated. Was ju=
st scoping out a small mains powered bulb, and it definitely
exhibited an afterglow of a full 45 seconds after power was removed, no=
t uniform across a bulb population, but close enough. It is
definitely using persistent phosphors. Needless to say one would need a=
laboratory grade high sensitivity instrument to detect
any flicker.

Lots of background info here:

https://pubs.acs.org/doi/pdf/10.1021/acsphotonics.8b00979

Another terrifying health hazard!

It\'s easy enough to get a photodiode and a scope and see light
waveforms. Do you have an oscilloscope?

I bought a few jugs of various color glow-in-the-dark paints from
Amazon, and pulsed them with a UV LED and scoped the optical
waveforms. They appeared to be zero-delay, zero persistance, to around=

5 ns resolution.

I have seen a small afterglow from fluorescent tubes.

The warm-white LED spot lamp just above my desk here has zero visible
afterglow.

Never sit under an Aspen tree on breezy, sunny days. The light flicker=

will kill you. Avoid all rapid eye movements, ditto sure death.
Campfires flicker and are lethal too.
I think my monitor has a LED backlight, it changes brightness all the tim=
e
when working.
Same for my laptop.
But I did switch off the auto brightness feature in the laptop,
annoying changing all the time.
And my room LED lighting is in fact PWM controlled:
https://panteltje.nl/panteltje/pic/ethernet_color_pic/

Some of these high end light fixtures that program intensity and color temp=
erature of the light source are ridiculously expensive.


Some LED lights have no converter chip but run directly from AC,
https://panteltje.nl/pub/LED_light_circuit_diagram_IMG_6925.JPG
the capacitor on the left limits the current
So any current spike will cause a flash.. and kill the LED as in my case.=

So avoid that type.
https://panteltje.nl/pub/LED_light_fix_IMG_6918.JPG

Except for the susceptibility to being destroyed, that looks like a pretty =
good circuit.

Yes it was, for a few weeks, until the mains surge..
I had 2, the other one went the same way.
Were cheap ones from ebay.
Mains was full of spikes where I lived then, bit better here.