At what frequency does the human eye notice flicker?

62 posts / 0 new
Last post

Pages

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States
At what frequency does the human eye notice flicker?

Okay so power management in LED’s is achieved by turning the led on and off so fast the human eye doesnt notice it yet the total “on time” is essentially reduced by 50% therefore doubling the amount of time the LED can produce photons?

Now in a multiple LED scenario does the on time off time alternate in sync between LED’s where one is off while the other is on?

Would the operation be a linear function run in series or parallel among the given number of LED’s?

Okay now follow me on this;

If LED 1 has a max luminous output of X for Xx amount of time and known cooling rate of Y, how many LED’s would be needed to achieve a constant optical perception of X while operating at the minimal temperature of Yy to achieve maximum energy efficiency of Z and how would you write the equation?

hank
hank's picture
Offline
Last seen: 20 min 16 sec ago
Joined: 09/04/2011 - 21:52
Posts: 9494
Location: Berkeley, California

It’s somewhere between 50 and 500 cycles per second, depending on a great many things in cluding
the state of your liver
and the shape of the pulse
so perhaps the most important variable in your equation is the individual concerned.

Also, it’s not “cooling” that causes LED output to drop
and persistence of the individual phosphors in the mix on the emitter has a lot to do with how long they glow between pulses

tech
Offline
Last seen: 5 months 7 hours ago
Joined: 12/03/2015 - 15:04
Posts: 379

I like the thought process described, having multiple emitters in a light and “cycling” through them in contrast to having them on/off simultaneously. Since only one of the emitters is “on” at a time – clearly this should be more efficient? But also resulting in less overall output?

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

I agree. It is the lack of cooling. It is to my understanding that excess heat causes the output to “sag” or drop in luminous flux proportionately to the rise in heat. Please correct me if this is wrong.

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

Overall compared to what? Lets suppose that an XHP70 having 4 xml dies, each one capable of 1000+ lumens at startup, were cycled through in such a manner as described above. If the xhp70 were only advertised to operate at an output of 1000+ lumens but 1/4 the heat and 4 times the duration of an ordinary xml…. would that not be appealing?

hank
hank's picture
Offline
Last seen: 20 min 16 sec ago
Joined: 09/04/2011 - 21:52
Posts: 9494
Location: Berkeley, California

http://www.digikey.com/en/articles/techzone/2014/feb/led-color-shift-und...

So you are thinking of having several groups of emitters, driven separately, and you want the pulses staggered so only one group at a time is dark?

Remembering the shape of the pulse and the persistence of the phosphor both affect how long the emitter is bright and how fast it changes light to dark to light.

On heat, djozz and others here can show you how output varies with power, it’s an efficiency curve that rises then falls as power goes up, specific to each kind of emitter. I think most of what you’ll find here is tests with continuous rather than pulsed power though. This will find some examples — choose “image” in the results and search:
site:budgetlightforum.com chart power brightness efficiency

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

Hank,

Something to that effect. I would honestly like to see an MKR type emitter with XPL dies. I think that max luminous flux can be maintained at a constant at 1/4 thermal. Less heat = more efficient = etc…….

Also I would think there to be tactical applications in group and/or arrays where as a more diverse pattern spectrum is achievable. I have little experience in that area other than having been subjected to an intense high frequency burst of light that brought to my attention that indeed I was vulnerable.

dchomak
Offline
Last seen: 2 years 5 months ago
Joined: 03/17/2012 - 20:10
Posts: 4122
Location: Connecticut

The way to get the most lumens per watt for an XH-P70 is to run all 4 dies at a lower current continuously. Pulsing each individual die at a higher current for 1/4 the time will be less efficient. Remember that after a certain current and heat level all LEDs are less effcient.

Also, and HKJ pointed this out once and I will never forget it, pulsing thru a resistor will be less effcient.
4 times the current pulsed through a resistor for 1/4 of the time will result in more heat loss. 4 times to be exact.

Assume a 1 ohm resistor and 1 Amp. Watts = I^2 x R in this case 1^2 × 1 = 1 watt. Do that for a second and you get 1 Watt-second.
Now pass 4 amps thru that same 1 ohm resistor, pulsed for 1/4 second and you get 4^2 × 1 = 16 watt. Do that over a second and you would divide that 16 watts by 4 and you get 4 Watt – seconds.

So as far as efficiency is concerned, “slow and steady wins the race”

Angler
Angler's picture
Offline
Last seen: 5 months 3 weeks ago
Joined: 07/21/2014 - 21:30
Posts: 691
Location: South Carolina
dehc111 wrote:
Overall compared to what? Lets suppose that an XHP70 having 4 xml dies, each one capable of 1000+ lumens at startup, were cycled through in such a manner as described above. If the xhp70 were only advertised to operate at an output of 1000+ lumens but 1/4 the heat and 4 times the duration of an ordinary xml…. would that not be appealing?

I think this is flawed. 4 xml dies. On turned on at any given time. Produces the same amount of heat as a single xml die. Not 1/4 as you stated. It also produces the same amount of light as a single xml at any given time. So basically running an XHP70 on the level of a single non-pwm xml. I don’t see why this would be desirable.

And PWM is not the only way LED’s are regulated.

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

Angler I agree and disagree.

The overall heat is not the issue. I am looking for the threshold at which a single die produces its maximum luminous flux. The XHP was just an example. Actually the LED’s dont even have to be on the same die.

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

I think everyone is missing my point. Go back to the opener of this thread and read the first post again.

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada

As others have stated, PWM is less efficient than producing the same (average) lumens by using a lower constant-current. So I’m not sure why you’d want to try to mimic a constant-current by some complex alternating PWM algorithm using multiple LEDs. All you’ll end up with is a more expensive and less efficient light, that will have lower overall output.

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

walkintothelight perhaps you are right. but if that were the case why have an array of LED’s at all? And within that array you say that there is no other manner, method, theory, strategy, idea, concept, or thought that could make better the array and how energy efficient it is or how much light is puts out? Have we actually become the GODS of LED efficiency?

Im not trying to be a smarta$$ for real… I appreciate everyone’s comments on this subject. I encourage it. I want to stimulate your thought.

Still nobody has even attempted to construct an equation as mentioned in the very first post. The model is real, the values are relevant, and the product I promise has significance.

“Complications” are not incorporated into anything without justification. I mean who would have thought that a computer chip would power our flashlights of today, twenty years ago………..

I need more input…….

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada
dehc111 wrote:
walkintothelight perhaps you are right. but if that were the case why have an array of LED’s at all?

You mean why use multiple LEDs? Simply: it allows for higher output, for very obvious reasons. Also, it could result in greater efficiency at a given (lower) output, because you’re driving each LED (at a constant current) less hard than you would a single-emitter light.

Quote:
And within that array you say that there is no other manner, method, theory, strategy, idea, concept, or thought that could make better the array and how energy efficient it is or how much light is puts out? Have we actually become the GODS of LED efficiency?

We already pointed out why your idea would not work in practice. But if you come up with another theoretical idea, by all means, state it, and maybe it really would work. Just be aware, like with perpetual energy machines, some may sound like a good idea on paper, but in reality can not work.

Quote:
Still nobody has even attempted to construct an equation as mentioned in the very first post. The model is real, the values are relevant, and the product I promise has significance.

Nobody came up with an equation, because your idea doesn’t make sense.

Quote:
“Complications” are not incorporated into anything without justification. I mean who would have thought that a computer chip would power our flashlights of today, twenty years ago………..

There is a theoretical maximum efficiency you can achieve with light output. A 100% efficient green light source (most sensitive to our eyes, thus having the highest lumens), is somewhere around 650 lumens/watt. (I forget the exact number, or where I read it, but is was around that level.)

That has nothing to do with PWM or anything like that. It’s just basic physics.

If you come up with an idea, the first thing you have to ask yourself is if it violates known physics. If it does, you have to rewrite known physics, before your idea will be taken seriously.

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada

That said, if I was going to come up with an idea to use PWM to increase efficiency of perceived light, I might do it something like a camera flash. A brief pulse of light would allow us to see quite a bit, even if the total energy used is fairly small (certainly much smaller than a constant source of light).

Perhaps there’s a point where you can increase the flash rate to a point where the human eye can no longer perceive it as flashing, while still using less energy than a constant light source would use.

It wouldn’t violate any physics, but might trick us into seeing more while using less power for the light source.

Or, it might be total B.S. I have no idea. I tend to think it’s B.S., though, as our retinas still have to turn light energy into electrical energy to send to our brains. Less light energy probably means less electrical signals triggered.

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

walkintothelight, Thank you for the insight. I will have re-read my own questions because the flash is exactly how this conversation was started I thought. Or that is at least the concept I was trying to convey. let me check

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada

Well, just keep in mind that “500 lumens using PWM” looks an awful lot like “500 lumens using constant current”. So, at least at the PWM frequencies that are typically used, our brains are not fooled into seeing anything more.

I tend to think that by the time PWM is showing us more (by slowing the rate), the flickering would be getting very annoying. Kind of like a strobe in a night club.

hank
hank's picture
Offline
Last seen: 20 min 16 sec ago
Joined: 09/04/2011 - 21:52
Posts: 9494
Location: Berkeley, California

As noted earlier, flicker fusion can’t be specified generally for use in an equation — it’s specific to any one individual/health/age
https://www.google.com/search?q=flicker+fusion+aging+variation

And PWM isn’t the theoretically pure square waves — even if that’s the intent, there’s some noise up and down. They can be sawtooth pulses, etc.

And each phosphor used in the emitter has its own persistence.

Specify those and build one, and you might be able to craft an equation — after empirically determining the values that come out of the circuit, and the phosphors, and the flicker rate perceived by the subject.

This is why cheap drivers use visible (low-rate) PWM, and why better drivers, if they use PWM, use a much higher frequency, to stay well out of the, er, gray zone where some people will see it.

Building a light with say three cheap low-rate-PWM drivers, each somehow coordinated with the others to keep their notches from lining up, might theoretically work. But egad.

Now remember, I’m some guy on the Internets and know nothing about this stuff, so you may find better advice from someone else.

Angler
Angler's picture
Offline
Last seen: 5 months 3 weeks ago
Joined: 07/21/2014 - 21:30
Posts: 691
Location: South Carolina

wight wrote:

PWM output to an LED is always less efficient than a smooth constant current output. The LED becomes less efficient at higher currents. An LED operating at an average of 1 amp using 50% duty cycle PWM is actually operating at 2 amps half the time and 0 amps the other half of the time. Let’s say that the LED is 60% efficient at 1 amp and 45% efficient at 2A. You’re getting 45% efficiency now with the PWM when you could be getting 60% if you had constant current!

maukka
maukka's picture
Offline
Last seen: 3 hours 48 min ago
Joined: 12/31/2015 - 04:15
Posts: 2164
Location: Finland

Angler wrote:
wight wrote:

PWM output to an LED is always less efficient than a smooth constant current output. The LED becomes less efficient at higher currents. An LED operating at an average of 1 amp using 50% duty cycle PWM is actually operating at 2 amps half the time and 0 amps the other half of the time. Let’s say that the LED is 60% efficient at 1 amp and 45% efficient at 2A. You’re getting 45% efficiency now with the PWM when you could be getting 60% if you had constant current!

I think I have read somewhere that in this situation the light with the PWM will look brighter.

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada
maukka wrote:
I think I have read somewhere that in this situation the light with the PWM will look brighter.

Source?

Because, I’ve never seen PWM described that way. I think if it really did fool our eyes to give increased sensitivity, it would be much more popular and marketed heavily. And, efficiency ratings (on lower levels where PWM is used), would be much better than they are when tested. Granted, testing equipment wouldn’t be fooled, but I’ve never noticed that a 100 lumen PWM light lasts any longer than a 100 lumen constant-current light (it’s usually the opposite).

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

Okay I really like the conversation this has brought about. Everyone seems to have a valid point in some regard or another.

My point is this. If a flash of light lasts a known amount of time and is quantifiable in terms of brightness, temperature, current draw and is repeatable at lets say 500Mhz frequency, does the millisecond timing provide enough lapse for the LED to recover to cycle EXACTLY the same. YES because we haven’t put a limit on the millisecond recovery value.

Again, follow me on this: We all agree that the luminous output of an LED begins to diminish within milliseconds after being energized and reaching its apex output. That is the holy grail of LED performance. That single measure of time when an LED gives all it can. It is at that point the most efficient.

The performance curve.

Now explain to me that if an LED is on and off an equal amount of time during lets say a 1 minute frame at a rate 30 times per second that after 1 minute an equal amount of energy has been consumed from this arrangement as opposed to an LED that was provided constant current during the same. It may not use exactly half as much energy but indeed significantly less.

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.

Angler
Angler's picture
Offline
Last seen: 5 months 3 weeks ago
Joined: 07/21/2014 - 21:30
Posts: 691
Location: South Carolina
dehc111 wrote:
Btw, constant current indeed operates in pulses. All electrical current does. Hertz….its how we measure it.

I’m only replying to this part.

WHAT?

No.

So tell us what hertz your AC batteries operate at.

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada
dehc111 wrote:
Now explain to me that if an LED is on and off an equal amount of time during lets say a 1 minute frame at a rate 30 times per second that after 1 minute an equal amount of energy has been consumed from this arrangement as opposed to an LED that was provided constant current during the same. It may not use exactly half as much energy but indeed significantly less.

Again, I don’t think you’re going to see that in a real experiment. In reality, PWM has demonstrated itself to be less efficient than constant current. I don’t think there’s a special frequency that changes that. You haven’t given any plausible explanation why.

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

No, direct current does not operate in pulses. Alternating current is probably what you’re thinking of.

Angler
Angler's picture
Offline
Last seen: 5 months 3 weeks ago
Joined: 07/21/2014 - 21:30
Posts: 691
Location: South Carolina

Earlier in your OP it was about minimal temperature and maximum efficiency.
But now that doesn’t matter because it’s about max luminous flux. Right?

And suddenly your flashlights operate on alternating current.
Are you trolling?

Did you even read that PWM is less efficient than Constant current in the quote I posted by Wight?

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada

Angler wrote:
Earlier in your OP it was about minimal temperature and maximum efficiency.
But now that doesn’t matter because it’s about max luminous flux. Right?

And suddenly your flashlights operate on alternating current.
Are you trolling?

It doesn’t sound like he’s trolling. He’s putting in too much work for that.

I think he sounds more like someone trying to come up with a perpetual motion/energy design. That is, there’s no way to make it work, but some people won’t let that dissuade them.

pilotdog68
pilotdog68's picture
Offline
Last seen: 1 year 2 weeks ago
Joined: 05/30/2013 - 23:31
Posts: 6420
Location: Held against my will in IOWA, USA

I think(?) I understand what dehc111 is getting at.

Hypotheticals:

Yes we know that an LED is not at it’s most efficient when being pulsed at 6amps 50% cycle. 3amp CC is more efficient.

But let’s say the peak efficiency is at 2amps.

We could pulse 2amps at 50% cycle (net draw of 1amp) and in a perfect world it would be more efficient than running a constant current at 1amp.

The problem being that the pulse are not instant on/offs they are ramped with the LED not being as efficient on those ramps.

Am I getting both sides to an extent?

I agree that I think this is a fundamentally flawed venture.

You could easily calculate that if you want 6000 lumens, and your emitter does 800 lumens at it’s most efficient point, how many emitters and how much power you would need. No problem. But you still want to go CC, not pulsed.

My Favorite Modded Lights: X6R, S8 , X2R , M6, SP03

Major Projects:  Illuminated Tailcap, TripleDown/TripleStack Driver

ggf31416
Offline
Last seen: 2 hours 51 min ago
Joined: 02/25/2016 - 17:38
Posts: 504
Location: Uruguay

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.

hank
hank's picture
Offline
Last seen: 20 min 16 sec ago
Joined: 09/04/2011 - 21:52
Posts: 9494
Location: Berkeley, California

http://phys.org/news/2012-03-efficiency.html

Of no practical use, but … interesting

WalkIntoTheLight
Offline
Last seen: 1 day 2 hours ago
Joined: 12/05/2015 - 10:26
Posts: 2157
Location: Canada

hank wrote:
http://phys.org/news/2012-03-efficiency.html

Of no practical use, but … interesting

Also a very misleading title. All they’re doing is using heat from the environment to power the LED. It’s not greater than 100% efficiency.

dehc111
dehc111's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 09/11/2015 - 01:59
Posts: 118
Location: United States

LMAO AC batteries…. good one….. that made me lol for real.

I apologize as I didnt mean to abandon the topic…… At all. I am trying to find someone to understand where I am trying to take this. Between my poor vocabulary and marginal communication skills on the topic, slight ADHD ADD XYZ or wut ever i suffer from, I sincerely appreciate your attention. I assure you I am not trolling or the like. My time is as valuable as yours and in the end we will all have gained something from this.

Okay. All current does pulse. Let me define pulse I suppose. Pulsation is patterned vibration < down and dirty definition.

Matter of fact all matter in the known universe pulses. It is called resonate frequency. I wont go into an atomic theory here but this is a generally accepted concept.

Now that we have established that in fact DC current pulses lets explore managing or controlling this pulsation.

To keep the conversation focused I am trying to achieve maximum luminous output sustained. secondary would be efficiency and third heat.
I am not interested in perpetual energy or any far right experimental b.s. of the kind. (at least not in this thread on this forum)

Back to the equation… You think it has no relevance ? The values are not associative ? Please help me define which values are then.

Pages