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