At what frequency does the human eye notice flicker?

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dehc111
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ggf31416 wrote:
The problem is that if LEDs have an efficiency peak, it’s at an extremely low current (at least for Cree). Take any led from http://pct.cree.com/dt/index.html , I’m pretty sure that for all tested currents the efficiency lm/W decreases as the current increases. Also the efficiency lm/A (Current), which would be useful if you use a linear driver, seems to decrease monotonically as the current increases. I believe that most if not all leds follow the same pattern.

Low current as compared to what?

hank
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Low current as compared to higher current, empirically, e.g.

See also
http://www.digikey.com/en/articles/techzone/2012/jul/characterizing-and-...

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Okay but I don’t what the red line is representing? or the dashed line.

dehc111
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Good link Hank! Thank you.

The article discusses modifying the waveform to compensate for an AC circuit.

This is interesting because the AC mimics the on/off pwm this thread is exploring. What I find even more interesting about that article was the proposed change from 120mhz to 150mhz the EPA tried to mandate
because of a known negative effects or sensitivities that humans experience at ~ 120mhz.

Weaponize an LED’s in this frequency range? Isnt that the same frequency (120 mhz) that LED T.V.‘s utilize for rendering high definition 1080P?

Okay that will make a great topic for another thread!!!!!!!!!!!!

I knew there was some kind of relative association that exists.

Okay I need to think on this more so I can construct my questions from another perspective.

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i can see 120hz flicker in cheap n nasty bulbs.
and cant stand low refresh rates in old crt pc monitors.worse when it beats with other lighting.which in the store was 4 tube t12 magnetic troffers.when we had pc’s on display at the shop i had to go around and reset all of them.otherwise it was like a room of strobes to me.
nobody but me and our tech could see this. this varies by the individual and reading that link also whether they have cirrosis.which i do not.

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dehc111 wrote:

Now that we have established that in fact DC current pulses

We have?

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WalkIntoTheLight wrote:
dehc111 wrote:

Now that we have established that in fact DC current pulses

We have?

Not on my oscilloscope! Crazy
The resonant frequency of DC is zero.

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WalkIntoTheLight wrote:
dehc111 wrote:

Now that we have established that in fact DC current pulses

We have?

lol. It would be a matter of semantics at this point.

https://en.wikipedia.org/wiki/Electrical_resonance

I like you guys.

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dehc111 wrote:
WalkIntoTheLight wrote:
dehc111 wrote:

Now that we have established that in fact DC current pulses

We have?

lol. It would be a matter of semantics at this point.

https://en.wikipedia.org/wiki/Electrical_resonance

I like you guys.


DC Current doesn’t resonate or pulse. Read again the first line of the Wikipedia article you linked:
Wikipedia wrote:
Electrical resonance occurs in an electric circuit…
We do see some resonance in our drivers at times, showing up as ringing. DEL told us how to fix that, so it shouldn’t be a problem with any of the newest drivers developed by PD68, TA, and others. Big Smile

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dehc111 wrote:
But this isnt about energy, this is about achieving maximum luminous output.

energy efficiency is a bonus.

Btw, constant current indeed operates in pulses. All electrical current does. Hertz….its how we measure it.

My apologies if I sound rude, but I’m gonna be honest; those two sentences betray significant flaws in your understanding of the topic.

1. Energy efficiency and maximum luminous output are linked by the laws of thermodynamics. Efficiency and Efficacy are two separate variables, but again they are linked. To obtain the maximum possible light output, you must posses an LED with the maximum possible efficacy [approx 300lm/w], and then you must apply the maximum power possible to it (whilst keeping it’s efficacy constant by cooling it).
To even start talking about light output, you must first consider efficacy.

Relevant: http://m.phys.org/news/2010-08-white-super-high-luminous-efficacy.html

2. Direct current does not switch on and off, or vary in any oscillatory way. The word “Hertz” is to direct current what “quadrilateral” is to a circle. Absolutely unconnected.

But it helps everyone to discuss these things, so everyone can contribute positively to the discussion.

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No need to apologize. As I stated. I am ignorant with poor communication skills.

Anyway we are veering away from where I was trying to keep this directed but I must let you know that you are both correct and incorrect.

I will cite two more references. The first of which more or less coincides with your response. The second is the one of real interest.

http://www.ibiblio.org/kuphaldt/electricCircuits/AC/AC_1.html

http://electronics.stackexchange.com/questions/41915/is-frequency-for-dc...

Now can we continue with the focal point?

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Quote:
I don’t what the red line is representing? or the dashed line.

When you see a picture, hover the mouse pointer over it.

If the mouse pointer changes to an icon of a little white glove with a pointing finger, or something like that
this means the picture is also a clickable link.

In the case of the chart I posted, when you click the link, it takes you to the full article describing that chart and much else.
That chart is “Figure 3” and the text next to it says:

Quote:
Light output Light output of LED light sources increases with increasing drive current. However the efficiency, expressed in lumens per watt, is adversely affected. Figure 3 illustrates this relationship. LED lamps normally have a “Test” current listed on the product data sheets. This Test current is provided as a reference point for other technical information provided. Drive currents may be chosen at any current up to the maximum recommended current for the specific LED light source used.

So the red line that rises from left to right is the light output — numbers along the left side of the picture (lumens)
The black line that decreases from left to right is the efficiency (efficacy, lumens per watt)
The text under the bottom of the chart explains that’s the forward current in milliAmps, increasing from left to right.

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hank wrote:
Quote:
I don’t what the red line is representing? or the dashed line.

When you see a picture, hover the mouse pointer over it.

If the mouse pointer changes to an icon of a little white glove with a pointing finger, or something like that
this means the picture is also a clickable link.

In the case of the chart I posted, when you click the link, it takes you to the full article describing that chart and much else.
That chart is “Figure 3” and the text next to it says:

Quote:
Light output Light output of LED light sources increases with increasing drive current. However the efficiency, expressed in lumens per watt, is adversely affected. Figure 3 illustrates this relationship. LED lamps normally have a “Test” current listed on the product data sheets. This Test current is provided as a reference point for other technical information provided. Drive currents may be chosen at any current up to the maximum recommended current for the specific LED light source used.

i said ignorant not stupid hank. i read the article and followed up with a post.

we have gotten way left field on this. All I am trying to do is find a way to constantly maintain the peak output of an LED.

I will try to think of another way to express my thoughts. What I am trying to accomplish is not impossible.

But I have learned a lot from everyone. Thanks

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dehc111 wrote:
All I am trying to do is find a way to constantly maintain the peak output of an LED.
Well, that’s the easy part… just give it a constant stream of peak power… and some extreme cooling. Big Smile

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dehc111 wrote:
No need to apologize. As I stated. I am ignorant with poor communication skills.

Anyway we are veering away from where I was trying to keep this directed but I must let you know that you are both correct and incorrect.

I will cite two more references. The first of which more or less coincides with your response. The second is the one of real interest.

http://www.ibiblio.org/kuphaldt/electricCircuits/AC/AC_1.html

http://electronics.stackexchange.com/questions/41915/is-frequency-for-dc...

Now can we continue with the focal point?

You say the second link is of real interest. It is not.
Perhaps you should read the first comment on that link.

_ “Very clever, but that’s not how it works.

By your reasoning you should not only be able to make the frequency infinite, but also 4 Hz, or 100 Hz, or 2√

Hz, all at the same time, with the same signal. And that’s why you can’t do that: a repeating signal can have only 1 fundamental frequency, which is 1/period.

It would be the same as taking 2 periods of the 4 Hz sine and saying that that’s the period, because it also repeats, and then the signal would be 2 Hz. It can’t be 2 Hz and 4 Hz at the same time” _

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dehc111 wrote:
Now can we continue with the focal point?

Continue based on false and impossible concepts?
Because that is the only way to continue here.
You should go back and read every post in this thread,
trying to understand them rather than trying to refute them.

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> Quote: I don’t what the red line is representing? or the dashed line.

Remember — online, we’re writing for an audience, and some readers won’t get here for days or weeks or months in the future

When one person doesn’t understand, likely others coming along later may also not understand. So it’s, I hope, worth explaining even though YOU got it quickly.

You’ll see — from me and others — explanations you may feel insult your intelligence. They’re not for you.

Being brighter than average, you may be offended by explanations intended for younger or new readers.

Sorry it bothered you. It wasn’t about you.

The average reading level of US citizens for nontechnical subjects is 7th grade — lower for anything technical.
So we try to explain things in ways people can follow even if they’re having a hard time.

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dehc111 wrote:
All I am trying to do is find a way to constantly maintain the peak output of an LED.

1. Acquire array of high-efficacy LEDs (eg. 10 XHP70s)
2. Directly thermally bond them to a nitrogen-cooled, copper, convective heat exchanger. (Eg. big copper cold plate with liquid nitrogen circulating through it)
3. Power them with a high-current, low resistance power supply (eg. a big bank of LiPo batteries)
4. Use a gold-coated parabolic reflector to collect all of the light, and direct it outwards in a certain direction.

Then you will have the maximum possible light output.

…Not very portable though. Big Smile

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Angler – I agree. Any result of this discussion can only be based on assumptions and premises established at the beginning of the discussion, and information included during. While the discussed information is interesting and valuable in other contexts, it is not truly pertinent to the discussion, because the basis of the discussion is flawed.
One cannot accurately answer a broken question.

Hank – good point well said.

Dehc111 – earlier, you said the following: “All I am trying to do is find a way to constantly maintain the peak output of an LED.
I will try to think of another way to express my thoughts. What I am trying to accomplish is not impossible.”
I think that is quite a good summation of this discussion, but not for the reasons you might think. Obtaining the most light from an LED is very simple; feed a highly efficant LED lots of power, and keep it cool. That is not rocket science. You’re right in a way; what you’re trying to accomplish is possible – it already exists.
This discussion appears to be predicated on you trying to re-invent the wheel.

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I was trolling….

Just kidding.

Hank – ^5

Again thanks to everyone who posted to this thread. Very informative.

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Regarding the efficiency peak, user Tobias Bessert at CPF in 2013 found a peak at about 160 mA for XM-L2 (that’s a bit higher than low mode in a 8×7135 Convoy S2+) and about 50 mA for XP-G2.
Not exactly bright, but an efficiency peak nevertheless. Thread: Using power LED at low current levels

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-1

The DC line you so describe can in fact be “cut into pieces” by pulsing the DC current allowing “infinite” frequencies, with amplitude.

shareimprove this answer
answered Jul 20 ’14 at 3:14

Dr.Tim
1

I almost let you guys talk me out of my concept. Above is a comment made to the following reference link I posted earlier.

http://electronics.stackexchange.com/questions/41915/is-frequency-for-dc....

There seems to be a pretty solid understanding of electrical theory from the contributors to this thread but then again we are talking about electrical “THEORY”.

My idea is not flawed. Perhaps not defined correctly and my vernacular in error but the concept has merit .

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Sure it can be cut into pieces. Commonly called PWM. Commonly used for dimming. Less efficient than constant current. Please elaborate on what everyone is wrong about.

And what exactly are you getting at when you say “electrical theory”?
It’s not something that is open to interpretation.
The properties of electricity are well known, understood, and documented.
You seem to have a penchant for wanting to rewrite this sort of thing.

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Compare the reputations of the people posting comments at stackexchange. Weigh them.
One unidentifiable guy who posts a single comment ever isn’t a lot of support to rely upon.

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I think I can boil this all down for you with a simple analogy.

You know string lights for christmas trees?
You know how they make those lights that chase, that is, light up in sequence?
I think this is analgous to the over-complicated thing you’re trying to say.

You see a set of chasing lights is less bright than a set of constantly lit bulbs.
Because all of the bulbs are not lit at the same time.
And yes it uses less electricity, because all of the bulbs are not on at the same time.

There is a direct correlation between electricity used and light emitted.

These two things can not be separated.

They can only be mitigated by using more efficient bulbs.

You are trying to dream up some type of more efficient electricity.

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hank wrote:
Compare the reputations of the people posting comments at stackexchange. Weigh them. One unidentifiable guy who posts a single comment ever isn’t a lot of support to rely upon.

That is difficult to do. I have no idea who they may be although the last comment, and the one i quoted, was by a man who named himself “dr tim”.

The web sight itself seems legit and credible. I for one are not someone who thinks that something cant be done because I am told so. Throughout my life I have found that some things were indeed possible while most were as suggested not possible. If it were not for those of us who push the boundaries of the impossible then discovery would never exist. In the early twentieth century the head of the US Patent Office declined to issue any patents stating that everything had already been invented, or something to that effect.

I am not trying to reinvent the wheel as someone had suggested. Come to think of it though, the wheel has undergone many improvements over the years. Thank goodness, my car just wouldn’t be the same with rolling rocks under it.

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Angler wrote:
I think I can boil this all down for you with a simple analogy.

You know string lights for christmas trees?
You know how they make those lights that chase, that is, light up in sequence?
I think this is analgous to the over-complicated thing you’re trying to say.

You see a set of chasing lights is less bright than a set of constantly lit bulbs.
Because all of the bulbs are not lit at the same time.
And yes it uses less electricity, because all of the bulbs are not on at the same time.

There is a direct correlation between electricity used and light emitted.

These two things can not be separated.

They can only be mitigated by using more efficient bulbs.

You are trying to dream up some type of more efficient electricity.

You are comparing apples to wagon wheels. A Christmas tree string of lights is not plagued by heat, or limited power, or portability, or and end users quest to outshine the neighborhood unless your a Griswald.
On second thought the last string of lights i bought were LED.

Maybe the purpose of this discussion is to draw out alternatives that may be useful for other applications of the LED. I started this conversation looking for help to write an equation that would express the product for variables of a given problem.

Regardless of how flawed my idea may be, or technically impossible, or viably insignificant it is none the less a starting point for looking at something from a different perspective.

I completely understand why everyone thinks I am wrong and wasting my time on something that has already been worked on but here is my analogy: Why put multiple LED’s in a light when you can achieve the same thing from a single LED of higher power?

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Quote:
Compare the reputations of the people posting comments at stackexchange. Weigh them. One unidentifiable guy who posts a single comment ever isn’t a lot of support to rely upon.
Quote:
That is difficult to do

No, it is not difficult to do. Did you try?

Click on the userid/name of the person who posted the comment — it’s a link.

(In most browsers it will show up in a different color.)

Read the text that appears.

Compare “Dr Tim” whose (only, single ever, one) comment at the site seems to support you, to the reputations of the others commenting in the thread.

Weigh their reputations. I think Dr. Tim is having you on.

See also this.

I’m done with this one.

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dehc111 wrote:
Why put multiple LED’s in a light when you can achieve the same thing from a single LED of higher power?

Your point, your purpose, your questions and your intent have changed numerous times over the course of this thread. Literally every single time you reply. First it was about maximum efficiency. Not much later it wasn’t about that at all, it was about maximum luminance.

Now you want to know why use multiple led’s in a light?

I dare not even answer because you will straightaway get to searching for a reason that the answer is wrong, ignoring established science and logic, continuing to go in circles. Unsubscribed.

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