Q: how find specific LED

mpm <mpmillard@aol.com> wrote in
news:709bd8ff-c4d4-4f73-98ec-3fd2a85b95b3@googlegroups.com:

On Wednesday, March 18, 2020 at 10:30:00 AM UTC-4, Rick C wrote:

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the
current limiting.

Maybe "scanning" would have been a better term.
One section of the design has (8) LED's. Instead of having them
all on at once, I scan through them real fast so that only one is
on at a time. Thus, 1/8th the power.

But, I could also blink them. Instead of being constantly "on"
(to the eye), I guess I could flash them too, but that's going to
be confusing to the user, and probably violates the product specs.

Their nature is to 'fully' conduct once 'on'. However, their
nature is to also self destruct if the current is too high because
there is an internal drop and thus 'working voltage'.

Pulse width modulation is used because that way the diode can be
switched on and emit in its ideal operating range, and yet provide
the user with a reduced light output by cycling it on and off and
using 'duty cycle' to govern the resultant "level" of output on the
lumens side. The waveform matters. Turn on, but turn back off
before it has a chance to get to full on brightness, AND space out
segments of that method. So short on pulses with adjustable wait
space. At that point the short legnth on pulse can have its width
adjusted wider. And thus one has multiple points in a circuit in
which to affect an adjustable output. Most flashlights have fixed
modes which have such set points pre set. It looks like "half
brightness" until you use it on your bike at night and the street
lamp syncs in and out with its flashes.

Trying to do that with flat DC control on a device which like to
conduct real good when on? Not nearly as easy and a lot of blown
units later and the entire planet moved to PWM modes.

But fully current limited, and you should be able to get good life
out of it. Read its spec, and uhhh... follow it.

 

mpm <mpmillard@aol.com> wrote in
news:709bd8ff-c4d4-4f73-98ec-3fd2a85b95b3@googlegroups.com:

Maybe "scanning" would have been a better term.
One section of the design has (8) LED's. Instead of having them
all on at once, I scan through them real fast so that only one is
on at a time. Thus, 1/8th the power.

1/8 the light as well.

All 8 on is bright.

All 8 sequenced is one on with 8 times the shelf life, but still only
one on at any given moment, and they have no afterglow, so...

Ever see a cosmology guy on Youtube talking about the stars?

His show is called "What Da Math"

It is funny he says it so fast you can;t hear it all.

 

mpm <mpmillard@aol.com> wrote in
news:4735dea4-5039-4a5f-926e-0fec8be42375@googlegroups.com:

On Wednesday, March 18, 2020 at 11:37:23 AM UTC-4,
upsid...@downunder.com wrote:

Since you are talking about latching relays, it sounds like
sometimes some high power will flow through your device. Why not
steal some power from that circuit to power the ON indicators ?

OK, Now you're just getting medieval on it.

I didn't mention it, but our LDO that powers that part of the
circuit gets close enough to its max I-out limit that we avoid
throwing all the relays at once. Even with latching relays, that
keeps peak coil current demands low enough to squeak by / justify,
etc...

This particular build is a pain in the ass.

Use an opto-coupler to have a "monitor switch" on the coil without
loading, and run a little LED bus down through the gang of optos and
relays and source the tiny amount of power it would need for the
LEDs...

Out of thin air! Yeah... that's it. It really can't be that
much. Fire 'em directly. Microamps, man... really.

Have the relay firing charge up a cap or supercap diode isolated
from the coil that then fires the LED and has persistence that does
not require additional power for a given period.

Now THAT sounds pretty cool, IF you do not have too high a repeat
rate. You said latching, so... latching LEDs!

 

[Rick C]

On Wednesday, March 18, 2020 at 4:49:03 PM UTC-4, David Brown wrote:

On 18/03/2020 17:36, Rick C wrote:
On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown
wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C
wrote:
I'm not sure why you say that. Many car tail lights blink
the LEDs rather than dim the current between tail light and
brake light modes. I know this for a fact because I can see
it when I turn my eyes. I find it very distracting and
annoying.

I'm working on a rather large project right now where I will
have to blink the LED's in order to meet the power budget. If
that were all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the
current limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an
impression of higher brightness to the human eye than you'd get
with regulating the current. I haven't confirmed this in detail,
but I have heard somewhere that a 20% duty cycle at, say, 200 Hz
gives the equivalent apparent brightness of 100% duty cycle with
half the current.

So no reference???

I might try to find one if I get the chance. But it is certainly a
common technique.


I screwed up a board design using resistors that were too small and
the LEDs were quite bright. I dimmed them by duty cycle modulating
at about 20%. I think it was faster than 200 Hz, but still... I
would find this a hard concept to believe unless there is a reference
somewhere. I can't think of a mechanism in the eye that would
provide for perceived brightness being the same on a duty cycled
light but only if the flash rate were in some specific, small range.

The retina cells react stronger to a change in light intensity. So the
initial part of the flash causes a stronger reaction than later parts.
Thus the blinking looks brighter. But if the blinking is too fast, the
cells don't have the time to "reset" between on-times, reducing the
effect. The effect is biggest with slower blinking (though the higher
level processing in the brain, which emphasises changes and movement,
has a bigger contribution for very slow blinking - that's why bike
lights often blink, as I'm sure you know). But below about 100 Hz and
you can see the flickering if you move your eyes, and that gets annoying.


In fact, as contrary information, the tail lights of autos are often
dimmed exactly this way, but pulsing them. I find it immensely
irritating when I see a dozen tail lights as I move swing my view
across the road in front of me. I expect this flash rate is
somewhere around 100-1000 Hz and is being done specifically to dim
the lights.


Of course you dim them that way - it is the simplest and most efficient
method. You just have to reduce the duty cycle more than you would
otherwise expect from a simple linear calculation.

So the more I think about it, the less I am inclined to believe there
is any such effect making a blinking LED appear relatively brighter
than a solidly on LED at the same power levels. In fact, there
should be some effect, even if small, reducing the relative
brightness at high current levels.

Do you have any references other than "I have heard somewhere"?


Real life practice.

I can't claim to have done any measurements or scientific comparisons,
however.

That's what I thought. Your explanation is really just hand waving. I've never seen any indication the perception of brightness is affected in any way by blinking at rates that can't be seen such as >100 Hz.

--

Rick C.

+- Get 2,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[mpm]

On Wednesday, March 18, 2020 at 10:30:00 AM UTC-4, Rick C wrote:

> How does blinking the LED reduce power consumption compared to reducing the current? Seems to me it is a constant power/energy situation when taking into account the power/energy in the current limiting.

Maybe "scanning" would have been a better term.
One section of the design has (8) LED's. Instead of having them all on at once, I scan through them real fast so that only one is on at a time. Thus, 1/8th the power.

But, I could also blink them. Instead of being constantly "on" (to the eye), I guess I could flash them too, but that's going to be confusing to the user, and probably violates the product specs.

 

[mpm]

On Wednesday, March 18, 2020 at 7:03:56 PM UTC-4, mpm wrote:

Unrelated to this thread, but maybe touching on your comments about automotive LED taillights, have you ever noticed that traffic lights sometimes have multiple LED's out at once?

It got me wondering whether the designers had enough forethought when they designed the circuit board to make sure that if one or more of the LED driving circuits fail, you don't end up with a valid-looking visible traffic light:

For example, a green, round "Go" light, that unintentionally morphs into a right or left turn arrow, if any of the LED drivers fail. Yikes!!

Thankfully, all the ones I've ever seen do this (a population probably less than 20), the "missing" LED's were scattered about.

 

[mpm]

On Wednesday, March 18, 2020 at 11:37:23 AM UTC-4, upsid...@downunder.com wrote:

Since you are talking about latching relays, it sounds like sometimes
some high power will flow through your device. Why not steal some
power from that circuit to power the ON indicators ?

OK, Now you're just getting medieval on it.

I didn't mention it, but our LDO that powers that part of the circuit gets close enough to its max I-out limit that we avoid throwing all the relays at once. Even with latching relays, that keeps peak coil current demands low enough to squeak by / justify, etc...

This particular build is a pain in the ass.

 

[piglet]

On 18/03/2020 4:36 pm, Rick C wrote:

On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the
LEDs rather than dim the current between tail light and brake
light modes. I know this for a fact because I can see it when I
turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have
to blink the LED's in order to meet the power budget. If that were
all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the current
limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an impression
of higher brightness to the human eye than you'd get with regulating the
current. I haven't confirmed this in detail, but I have heard somewhere
that a 20% duty cycle at, say, 200 Hz gives the equivalent apparent
brightness of 100% duty cycle with half the current.

So no reference???

I screwed up a board design using resistors that were too small and the LEDs were quite bright. I dimmed them by duty cycle modulating at about 20%. I think it was faster than 200 Hz, but still... I would find this a hard concept to believe unless there is a reference somewhere. I can't think of a mechanism in the eye that would provide for perceived brightness being the same on a duty cycled light but only if the flash rate were in some specific, small range.

In fact, as contrary information, the tail lights of autos are often dimmed exactly this way, but pulsing them. I find it immensely irritating when I see a dozen tail lights as I move swing my view across the road in front of me. I expect this flash rate is somewhere around 100-1000 Hz and is being done specifically to dim the lights.

So the more I think about it, the less I am inclined to believe there is any such effect making a blinking LED appear relatively brighter than a solidly on LED at the same power levels. In fact, there should be some effect, even if small, reducing the relative brightness at high current levels.

Do you have any references other than "I have heard somewhere"?

I too remember seeing that and found it in the HP Optoelectronics
Applications Manual from 1977 ISBN 0-07-028606-X in section 2.3.4

The key fact is that LED intensity is actually slightly supra-linear
with forward current. Exponent varies from 1.1 to 1.4 depending on LED -
but 40+ years on that may have changed a lot?

piglet

 

[mpm]

On Wednesday, March 18, 2020 at 7:30:25 PM UTC-4, DecadentLinux...@decadence.org wrote:

mpm wrote in
news:709bd8ff-c4d4-4f73-98ec-3fd2a85b95b3@googlegroups.com:

Maybe "scanning" would have been a better term.
One section of the design has (8) LED's. Instead of having them
all on at once, I scan through them real fast so that only one is
on at a time. Thus, 1/8th the power.


1/8 the light as well.

Yes, it is a little bit dimmer, but not objectionably so.

 

[Rick C]

On Thursday, March 19, 2020 at 5:45:32 AM UTC-4, piglet wrote:

On 18/03/2020 4:36 pm, Rick C wrote:
On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the
LEDs rather than dim the current between tail light and brake
light modes. I know this for a fact because I can see it when I
turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have
to blink the LED's in order to meet the power budget. If that were
all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the current
limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an impression
of higher brightness to the human eye than you'd get with regulating the
current. I haven't confirmed this in detail, but I have heard somewhere
that a 20% duty cycle at, say, 200 Hz gives the equivalent apparent
brightness of 100% duty cycle with half the current.

So no reference???

I screwed up a board design using resistors that were too small and the LEDs were quite bright. I dimmed them by duty cycle modulating at about 20%. I think it was faster than 200 Hz, but still... I would find this a hard concept to believe unless there is a reference somewhere. I can't think of a mechanism in the eye that would provide for perceived brightness being the same on a duty cycled light but only if the flash rate were in some specific, small range.

In fact, as contrary information, the tail lights of autos are often dimmed exactly this way, but pulsing them. I find it immensely irritating when I see a dozen tail lights as I move swing my view across the road in front of me. I expect this flash rate is somewhere around 100-1000 Hz and is being done specifically to dim the lights.

So the more I think about it, the less I am inclined to believe there is any such effect making a blinking LED appear relatively brighter than a solidly on LED at the same power levels. In fact, there should be some effect, even if small, reducing the relative brightness at high current levels.

Do you have any references other than "I have heard somewhere"?


I too remember seeing that and found it in the HP Optoelectronics
Applications Manual from 1977 ISBN 0-07-028606-X in section 2.3.4

The key fact is that LED intensity is actually slightly supra-linear
with forward current. Exponent varies from 1.1 to 1.4 depending on LED -
but 40+ years on that may have changed a lot?

piglet

I can't find an accessible copy. Mostly this is in paper form.

Thanks anyway.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[mpm]

On Thursday, March 19, 2020 at 12:33:17 PM UTC-4, Rick C wrote:

On Thursday, March 19, 2020 at 5:45:32 AM UTC-4, piglet wrote:
On 18/03/2020 4:36 pm, Rick C wrote:
On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the
LEDs rather than dim the current between tail light and brake
light modes. I know this for a fact because I can see it when I
turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have
to blink the LED's in order to meet the power budget. If that were
all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the current
limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an impression
of higher brightness to the human eye than you'd get with regulating the
current. I haven't confirmed this in detail, but I have heard somewhere
that a 20% duty cycle at, say, 200 Hz gives the equivalent apparent
brightness of 100% duty cycle with half the current.

So no reference???

I screwed up a board design using resistors that were too small and the LEDs were quite bright. I dimmed them by duty cycle modulating at about 20%. I think it was faster than 200 Hz, but still... I would find this a hard concept to believe unless there is a reference somewhere. I can't think of a mechanism in the eye that would provide for perceived brightness being the same on a duty cycled light but only if the flash rate were in some specific, small range.

In fact, as contrary information, the tail lights of autos are often dimmed exactly this way, but pulsing them. I find it immensely irritating when I see a dozen tail lights as I move swing my view across the road in front of me. I expect this flash rate is somewhere around 100-1000 Hz and is being done specifically to dim the lights.

So the more I think about it, the less I am inclined to believe there is any such effect making a blinking LED appear relatively brighter than a solidly on LED at the same power levels. In fact, there should be some effect, even if small, reducing the relative brightness at high current levels.

Do you have any references other than "I have heard somewhere"?


I too remember seeing that and found it in the HP Optoelectronics
Applications Manual from 1977 ISBN 0-07-028606-X in section 2.3.4

The key fact is that LED intensity is actually slightly supra-linear
with forward current. Exponent varies from 1.1 to 1.4 depending on LED -
but 40+ years on that may have changed a lot?

piglet

I can't find an accessible copy. Mostly this is in paper form.

Thanks anyway.

You can find it on Scribd. (www.scribd.com), which is subscription based, but well worth the money.

Link: https://www.scribd.com/search?content_type=documents&page=1&query=HP%20Optoelectronics%20&language=1

The section 2.3.4 essentially claims that the human eye is a time averaging detector, and that the time average luminous intensity is what matters - and it may not match the area under the curve specified in the datasheet. (but will be typically close).

 

[Rick C]

On Thursday, March 19, 2020 at 8:44:14 PM UTC-4, mpm wrote:

On Thursday, March 19, 2020 at 12:33:17 PM UTC-4, Rick C wrote:
On Thursday, March 19, 2020 at 5:45:32 AM UTC-4, piglet wrote:
On 18/03/2020 4:36 pm, Rick C wrote:
On Wednesday, March 18, 2020 at 11:41:16 AM UTC-4, David Brown wrote:
On 18/03/2020 15:29, Rick C wrote:
On Wednesday, March 18, 2020 at 7:52:57 AM UTC-4, mpm wrote:
On Wednesday, March 18, 2020 at 2:26:19 AM UTC-4, Rick C wrote:
I'm not sure why you say that. Many car tail lights blink the
LEDs rather than dim the current between tail light and brake
light modes. I know this for a fact because I can see it when I
turn my eyes. I find it very distracting and annoying.

I'm working on a rather large project right now where I will have
to blink the LED's in order to meet the power budget. If that were
all I had to do, then OK.

How does blinking the LED reduce power consumption compared to
reducing the current? Seems to me it is a constant power/energy
situation when taking into account the power/energy in the current
limiting.


Blinking an LED fast ( > 100 Hz) but not too fast can give an impression
of higher brightness to the human eye than you'd get with regulating the
current. I haven't confirmed this in detail, but I have heard somewhere
that a 20% duty cycle at, say, 200 Hz gives the equivalent apparent
brightness of 100% duty cycle with half the current.

So no reference???

I screwed up a board design using resistors that were too small and the LEDs were quite bright. I dimmed them by duty cycle modulating at about 20%. I think it was faster than 200 Hz, but still... I would find this a hard concept to believe unless there is a reference somewhere. I can't think of a mechanism in the eye that would provide for perceived brightness being the same on a duty cycled light but only if the flash rate were in some specific, small range.

In fact, as contrary information, the tail lights of autos are often dimmed exactly this way, but pulsing them. I find it immensely irritating when I see a dozen tail lights as I move swing my view across the road in front of me. I expect this flash rate is somewhere around 100-1000 Hz and is being done specifically to dim the lights.

So the more I think about it, the less I am inclined to believe there is any such effect making a blinking LED appear relatively brighter than a solidly on LED at the same power levels. In fact, there should be some effect, even if small, reducing the relative brightness at high current levels.

Do you have any references other than "I have heard somewhere"?


I too remember seeing that and found it in the HP Optoelectronics
Applications Manual from 1977 ISBN 0-07-028606-X in section 2.3.4

The key fact is that LED intensity is actually slightly supra-linear
with forward current. Exponent varies from 1.1 to 1.4 depending on LED -
but 40+ years on that may have changed a lot?

piglet

I can't find an accessible copy. Mostly this is in paper form.

Thanks anyway.


You can find it on Scribd. (www.scribd.com), which is subscription based, but well worth the money.

Link: https://www.scribd.com/search?content_type=documents&page=1&query=HP%20Optoelectronics%20&language=1

Can't read that of course.

> The section 2.3.4 essentially claims that the human eye is a time averaging detector, and that the time average luminous intensity is what matters - and it may not match the area under the curve specified in the datasheet. (but will be typically close).

Not sure what you mean by "may not match...", but if "the human eye is a time averaging detector" then running the LED at 8 times the brightness for 1/8 the time will accomplish nothing in terms of saving power and in fact will waste some small power in the control mechanism.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

 

[Jasen Betts]

On 2020-03-18, mpm <mpmillard@aol.com> wrote:

On Wednesday, March 18, 2020 at 10:30:00 AM UTC-4, Rick C wrote:

How does blinking the LED reduce power consumption compared to reducing the current? Seems to me it is a constant power/energy situation when taking into account the power/energy in the current limiting.

Maybe "scanning" would have been a better term.
One section of the design has (8) LED's. Instead of having them all on at once, I scan through them real fast so that only one is on at a time. Thus, 1/8th the power.

use inductors instead of resistors, that will get you increased
brightness at the same supply current, but it's probably cheaper to use
high-effiency LEDs in most cases


--
Jasen.

 

[Jasen Betts]

On 2020-03-18, DecadentLinuxUserNumeroUno@decadence.org <DecadentLinuxUserNumeroUno@decadence.org> wrote:

mpm <mpmillard@aol.com> wrote in
news:4735dea4-5039-4a5f-926e-0fec8be42375@googlegroups.com:

On Wednesday, March 18, 2020 at 11:37:23 AM UTC-4,
upsid...@downunder.com wrote:

Since you are talking about latching relays, it sounds like
sometimes some high power will flow through your device. Why not
steal some power from that circuit to power the ON indicators ?

OK, Now you're just getting medieval on it.

I didn't mention it, but our LDO that powers that part of the
circuit gets close enough to its max I-out limit that we avoid
throwing all the relays at once. Even with latching relays, that
keeps peak coil current demands low enough to squeak by / justify,
etc...

This particular build is a pain in the ass.


Use an opto-coupler to have a "monitor switch" on the coil without
loading, and run a little LED bus down through the gang of optos and
relays and source the tiny amount of power it would need for the
LEDs...

Out of thin air! Yeah... that's it. It really can't be that
much. Fire 'em directly. Microamps, man... really.

Have the relay firing charge up a cap or supercap diode isolated
from the coil that then fires the LED and has persistence that does
not require additional power for a given period.

Now THAT sounds pretty cool, IF you do not have too high a repeat
rate. You said latching, so... latching LEDs!

use latching relays with visible state indication, use no LEDs

--
Jasen.

 

Jasen Betts <jasen@xnet.co.nz> wrote in news:r56ahq$s3e$2
@gonzo.revmaps.no-ip.org:

use latching relays with visible state indication, use no LEDs

Well, then go all out and make those emechanical window flags
actaully raise an external 'flag' (lever) on the front panel. One
glance and status is clear to the observer... NOT! LED's on the other
hand, CAN be observed from a distance and status derived.

So, sure... if the operator has to be there at the rack anyway,
mechanical status relays would work, but the design would require
placing them in a row, visible from holes in the front panel. That
rules out any abilty to tell at a glance from a distance.

Best to go back to my opto-coupler triggers, and make an Iot BT
device to send it off to another device. No LED current usage.

 

[mpm]

On Saturday, March 21, 2020 at 8:32:53 PM UTC-4, Jasen Betts wrote:
> use latching relays with visible state indication, use no LEDs

Interesting idea.
I'm not aware of any inexpensive (or otherwise?) small signal -type relays that fit that bill. The max it would save is ~ 700 uA x 8 LED's. Not enough to mess with (yet).

I recovered another 6 mA in the power budget by NOT letting the 5VDC-to-3VDC isolated regulator run full time. It's only needed when it's needed (about 5% duty cycle), and it turns out I can live with the start-up time. So, we'll switch it on with a FET under microprocessor control.

With the present numbers, I think we can avoid some of the more complicated software power-saving routines and be OK. But that isolated supply was really the last of the low-hanging fruit. Further cuts would become noticeable to the end user (but might still be acceptable if it really comes to that.)

Right now, the power budget (simulated) has us at about 29 hours (need 24).
This product will go in for UL approval, so I'm sure they're going to put a stopwatch on it.

 

[Robert Baer]

Robert Baer wrote:

Phil Hobbs wrote:
On 2020-03-11 09:11, George Herold wrote:
On Tuesday, March 10, 2020 at 11:43:23 PM UTC-4, Robert Baer wrote:
I had one red T-1 3/4 (5mm) clear LED that was rather bright at 50uA
and it failed. Have no other than this.

    Mouser online catalog was not helpful, and i seriously doubt
DigiKey
would be better.
    I see specs like 45mcd unknown current, 5000mcd 30mA, 2000mcd 20mA,
high intensity red, etc.

    I got a little desperate, bought various Cree 5mm clear red LEDs
apparently all 500mcd 20mA...but dim as all heck at 50uA.
    One of their standard LEDs was twice as bright as some of their
high
intensity LEDs.
    And i stupidly thought that Cree had brighter LEDs.
    ROHM and Everlight look better, but i need to use 250uA to drive
them
to visually similar intensity WRT my "reference".

    Hell, the LED in the Dollar Tree LED Flashlight and Lantern1-3/4 LE
Combination SKU: 286458 visually equaled the intensity at 25uA (white,
clear, gigantic size).

    Would like red, 5mm, bright at 50uA.

    Ideas?
    Thanks

Digikey's search engine is ~100x better than mouser's.
I'm not sure any place will give you the intensity at such low current.

Is there some reason you can't increase the current?

George H.

IME modern T1-3/4 LEDs usually have a knee at about 10 uA and are
pretty linear above that.  So once the OP figures out what he means by
'reasonably bright', especially the solid angle/brightness tradeoff,
it's reasonable to take the datasheet candela value, multiply by the
ratio

(50 uA - 10 uA knee)/(datasheet current).

Cheers

Phil Hobbs

  Does not explain the WIDE discrepancy i saw:
  Suggest you look at the "comparison" of a 45 mcd VS 5000 mcd LED.
  Everlight 45 mcd: 10uA reads 18.5Meg, 25uA reads 4.56Meg, 50uA reads
1.73Meg.
  ROHM 5000 mcd: 10uA reads 7.6Meg, 25uA reads 1.86Meg, 50uA reads
0.41Meg.
  Note the 45 mcd at 50uA reads near what the 5000 mcd at 25uA.

Check out a better comparison chart; no nonlinear CDS photo resistor;
used a LED for detector for better linearity.
See attached Red5mmLEDs.xls for info.

Have on order the highest intensity CREE red LED available
(C503B-RAN-CA0B0AA1) and the highest intensity Kingbright red LED
available (WP7113SEC/J3) at Mouser.

Thanks

 

[Robert Baer]

Robert Baer wrote:

Robert Baer wrote:
Phil Hobbs wrote:
On 2020-03-11 09:11, George Herold wrote:
On Tuesday, March 10, 2020 at 11:43:23 PM UTC-4, Robert Baer wrote:
I had one red T-1 3/4 (5mm) clear LED that was rather bright at 50uA
and it failed. Have no other than this.

    Mouser online catalog was not helpful, and i seriously doubt
DigiKey
would be better.
    I see specs like 45mcd unknown current, 5000mcd 30mA, 2000mcd
20mA,
high intensity red, etc.

    I got a little desperate, bought various Cree 5mm clear red LEDs
apparently all 500mcd 20mA...but dim as all heck at 50uA.
    One of their standard LEDs was twice as bright as some of their
high
intensity LEDs.
    And i stupidly thought that Cree had brighter LEDs.
    ROHM and Everlight look better, but i need to use 250uA to
drive them
to visually similar intensity WRT my "reference".

    Hell, the LED in the Dollar Tree LED Flashlight and
Lantern1-3/4 LE
Combination SKU: 286458 visually equaled the intensity at 25uA (white,
clear, gigantic size).

    Would like red, 5mm, bright at 50uA.

    Ideas?
    Thanks

Digikey's search engine is ~100x better than mouser's.
I'm not sure any place will give you the intensity at such low current.

Is there some reason you can't increase the current?

George H.

IME modern T1-3/4 LEDs usually have a knee at about 10 uA and are
pretty linear above that.  So once the OP figures out what he means
by 'reasonably bright', especially the solid angle/brightness
tradeoff, it's reasonable to take the datasheet candela value,
multiply by the ratio

(50 uA - 10 uA knee)/(datasheet current).

Cheers

Phil Hobbs

   Does not explain the WIDE discrepancy i saw:
   Suggest you look at the "comparison" of a 45 mcd VS 5000 mcd LED.
   Everlight 45 mcd: 10uA reads 18.5Meg, 25uA reads 4.56Meg, 50uA
reads 1.73Meg.
   ROHM 5000 mcd: 10uA reads 7.6Meg, 25uA reads 1.86Meg, 50uA reads
0.41Meg.
   Note the 45 mcd at 50uA reads near what the 5000 mcd at 25uA.
  Check out a better comparison chart; no nonlinear CDS photo resistor;
used a LED for detector for better linearity.
  See attached Red5mmLEDs.xls for info.

  Have on order the highest intensity CREE red LED available
(C503B-RAN-CA0B0AA1) and the highest intensity Kingbright red LED
available (WP7113SEC/J3) at Mouser.

   Thanks
Extended chart:

Item Mfg Part Comment
2 CREE C503B-RBS-CY0Z0AA1 STD
10 ROHM SLI-580UT3F STD
12 VCC UAOL-3GRE4 HIGH
11 TT ELECT OVLLR8C7 STD
4 CREE C503B-RBN-CW0Z0AA1 STD
5 CREE C503B-RBN-CW0Z0AA2 STD
6 CREE C503B-RBS-CW0Z0AA2 STD
3 CREE C503B-RBN-CY0Z0AA2 STD
7 CREE C503B-RBN-CX0Y0AA1 STD
1 LITE-ON LTL-307EE RED lens
9 CREE C503B-RBN-CX0Y0AA1 PINK lens
13 CREE C503B-RBN-CX0Y0AA1 RED lens
101 CREE C503B-RAN-CA0B0AA1 STD
102 KingBright WP711SEC/J3 STD

Driver LED d1 comparisons with LED d2 detector measurement
Adjustable 20V supply in series with 750K resistor and d1
DVM used to measure d2

d1 d2 Detector voltage
2 2 1.335
10 2 0.324
12 2 0.396
11 2 0.441
4 2 1.239
5 2 1.287
6 2 1.297
3 2 1.084
7 2 1.237
8 2 1.210
6 6 1.204

New detector setup
d1 d2 Detector voltage
2 2 1.326
2 101 1.263
2 102 1.283

So, luminance info is not primary factor for detector sensitivity.
Seems I stumbled on one of the better CREE LEDs for the detector.


The CREE C503B-RBS-CY0Z0AA1 (standard LED, #2) is definitely
visible (in relatively dark room) at 0.16uA, supply 4.95V, 22 Meg
resistor in series. That calculates to 1.43V across the LED!