Is anyone familiar with driving large RGB led grids. Such as 32x32 using cascaded LED drivers. Actually my specific grid is 24x19(each point is one led and not an rgb). I have seen 24-ch led drivers along with 16-ch x 8-com(for 128 total led's).
Think of the grid as a led matrix display panel as essentially it is what it is. If I use 24-ch drivers then it requires 19 IC's. Some chips have built in PWM, dot correction, and other nice features but at a premium. I do not need error checking but thermal overload shutdown would be nice.
Using a matrix would be much cheaper as I could use 1 24-ch driver and
19 fets, one for each row. The main issue I am worry about here is the duty cycle required for each led row and power requirements for the driver(which I can split the rows up to reduce the power consumption).
If I require a nominal 10mA per led then this is 4.5A and approximately 20W's total dissipation. I'm not quite sure how to calculate the power dissipated by the IC. I would like to increase the nominal current to 20mA if possible just for headroom in case it is eventually required.
The only problem here is that it requires a duty cycle of 1/19 which bumps up the peak current to approximately 200mA. Does this seem pretty extreme? The peak current at 1/10 @ 1Khz is R=60mA, G=B=100mA. So this seems to be pushing it assuming I can extrapolate linearly.
If it's too much I can split the grid into two or three but I'd like to do it all at once.
What kinda of effect does using PWM have on the led optics? Does the intensity and color end up changing or can I expect a fairly consistent output over a wide range of duty cycles?
Are there issues with low current? I've heard of pre-charged fets but not sure exactly what they do. I would like to operate the driving chips for grayscale.
I guess the real question I'm asking is if running a 24x19 grid is easily done off one or two drivers. My original thought was to use as many drivers as needed and take advantage of the features they have except it seems awful expensive just to drive the grid.
The data sheet gives a duty of 1/10 of 100mA so surely this means that it is workable? Is this just a hypothetical? I have seen datasheets for drivers that have 8com and hence can do nx8 which gives a duty cycle of 1/8. Am I just using the wrong led's or are these datasheets exaggerating?
I have experience _using_ them. Not designing them. Electronics is a hobby of mine, not a profession.
The chips I've used do use PWM and other 'nice features.' They were arranged as 8x16 drivers (1/8th period . The ones I used were in a
16x16 module and they used 6 ICs, two to make up a 16x16 of one color and three sets of these pairs for the tri-color LED system. Separate power supply rails for each color, to reduce power consumption. Each
16x8 graphics module IC included RAM, an address decoder, the mux circuitry, and constant current drivers with their 7-bit current value stored in non- volatile memory, including column staggering to reduce EMI, interdigit blanking time, etc. The constant current drivers set the maximum current value and the PWM was used to reduce the intensity from there. It included over-temp shutdown and also a kind of deadman thing where if the external clock wasn't present for 30ms, it would also shut down. The ICs were custom, but the whole 16x16x3 module, with heatsink and 6 ICs built into it was about $80 to the customer, years ago.
Power requirements were nasty. It supported up to about 2.5A per color, for a total of 7.5A. The red supply (typical) was 4V, the blue and green were 5.75V. The dissipation for the 16x16 was, as you can see, nearing 40W. (That's all 6 ICs.) The actual, considering that not LEDs were on all the time or at full brightness, was less than half that. But it had a heat sink of its own that was intended to be bolted into something else to help out. And sometimes you wanted everything ON, so it had to handle worst case -- at least for some time.
Yes. It's pretty extreme. I thought x8 was pushing things. Worked okay, I admit. But I'd probably not push things harder than that without good experimentation to support more, first. You actually lose something in the process, too. LEDs do gain a little in brightness, keeping average current a constant, if you raise the peak current and reduce down from 100% duty. But only up to a small bit. Maybe 50% duty and twice the average? Something like that. After that, it goes back downhill again. For some LEDs, anyway.
Split the grid. Use identical drivers, chained up together. Make them yourself.
With 1/8th (8 by), you might consider 32 PWM intensity steps as adequate. I don't know your application, though. The choice of what those steps should be... well, that's up to you. And no, don't expect consistent output from different LEDs, even if they are from the same manufacturer and same batch. (Unless they tell you that they bin them, first.) They generally won't look the same side-by-side at the same current and same duty cycle. At least, not to me. I had to bin the damned things, myself, on both color and intensity.
What seems simple to imagine at first can get hairy fast.
You really sound like you are biting off more than you can chew. I designed the MAX7219, but it doesn't sound applicable for your application.
Regarding PWM, there are two schools of thought, both which have been discussed on SED. Some claim the eye retains the peak value, so as you PWM, it it does not look linear. Others say the eye averages perfectly. Who knows. An old HP app note claims the eye maintains the peak value.
Regarding power dissipation. it really is straight forward. You know the current in the LED. You need to know the drop across the LED, as well as the tempco of this voltage. Once you know the voltage across the LED, then the remaining supply voltage is dropped across the chip. P=3DVI. Do the worst case of all LED on. Next you need to know the theta junction to ambient of the chip. It should be specified by the manufacturer, though your layout effects it a bit.You need to pick the highest ambient temperature you expect the chip to be in. This generally isn't all that high since presumably a human being will be viewing the display. Say 140 deg F.. [Few places on earth get to 120 deg F, so that give you some margin.] Convert 140 deg F to 60 deg C. Pick a target for the die temperature and see if it fits the chip limit. If not, then you need to reduce the target "viewing" temperature or work out a heat sink scheme for the chips.
Unless the chip is in a special thermal package, most of the heat comes out the pins. [The package might have a thermal slug in it, which does release some heat from the package body. Generally a fat bonding wire is used since the heat flow is proportional to the crossectional area of the bond wire. ] You can marginally improve the theta JA by putting more copper on the traces to the chip. Even metal under the chip would help a bit.
Broadly speaking, the eye averages when the rate is fast. I've tested this and I have no question about it, anymore. (When it isn't fast, other obvious things come into play -- namely, you can see the flicker which pretty much changes the ball game, anyway.)
Anyone can purchase a copy of HP's "Optoelectronics: Fiber-Optics Applications Manual," 2nd edition, through alibris or some other bookseller outlet, and take a look at the quote in the last paragraph on page 5.25, "The human eye is a time average detector..." That quote is also from HP. In any case, it's clear enough through experiment, too.
...
That said, the effect of pulsing is not entirely net-zero. There is a suggestive curve on page 5.20 of the same book above, Figure 5.2.4-1, "Relative Luminous Efficiency (Luminous Intensity Per Unit Current) vs Peak Current Per Segment for a High-Efficiency Red Display." The curve shows increased luminous efficiency when pulsing vs DC, using the time-averaged current as the standard (until the LED junction nears saturation, which it will do at some point.)
Their example note that pulsing a high-efficiency red LED with 50mA at a 10% duty cycle (5mA time-averaged) yields a luminous intensity about
1.6 times as great as running the same LED at a constant 5mA. The curve for this red LED basically flattens out at 1.6, so higher pulse currents aren't helpful in this case.
Keep in mind that pulsing the LED with 50mA requires a higher drive voltage than if the same LED were run with a DC current equal to the time-averaged equivalent. For example, rather than 1.9V@5mA/100% it might be 2.6V@50mA/10%; which is 9.5mW and 13mW average, respectively. So although it may be 1.6 times brighter, it's also about 1.4 times the power. Some gain, but nothing to write home about and certainly not like some 10X brightness that a 'peak' response theory would suggest.
(Higher temperatures also lower output, on the order of 1%/C, roughly.)
On the other hand, if you have to drop voltage to control the current anyway, you might as well hand that over to the LED and make something out of it than just toss it all away in the regulation (or resistor) if you can afford the reduced overhead.
Anyway, my experience is consistent with the comments from HP's book.
Since you designed the MAX7219, you must have seen enough of all this on your own, by now. How is it that you remain ambivalent about the question?
On a sunny day (Tue, 8 Sep 2009 21:36:19 -0700 (PDT)) it happened " snipped-for-privacy@sushi.com" wrote in :
My experience shows clearly that the eye does average. That is why you can 'dim' a LED display with PWM. Seem pretty linear to me too, but I added adjustable gamma correction just for fun:
Does that make you feel more superior? How do you have any idea if it's more than I can handle or not? Because I asked some questions? Or maybe you believe it is difficult and hence can't see any lower life forms being able to do it? Or maybe your just taking after your messiah Obama?
The devil is in the details. But this is a somewhat common application and is not technically challenging. The biggest problem seems to be dot correction but it is not something difficult since I can simply compensate for led variance and even IC variance in software if needed (assuming I have some enough PWM steps). I do think that dot correction will not be an issue for my application in any event.
My main issue is simply one of economy. I have laid out the matrix using one channel per LED but this requires and ton lot of drivers. If I go with a fully featured driver the cost is somewhat astronomical. If I use simple drivers such as the
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rint/tlc59025.html which is bare bones it is about 6 times cheaper(from ~80$ to ~15).
By reducing the number of IC's means the complexity goes up. After all, I have to implement the PWM myself if I want to use a matrix based design because I can't pwm through multiple rows. I then also have to deal with finding the right way to divide the matrix so that I reduce the duty cycle and peak current to those that will work(which seems like I might have to do some testing to find the best way).
The refresh rate is only an issue in that the faster it is requires communicating faster with the ic's. It also changes the dynamics of driving. Is 100mA 10%@1kHz the same as 100mA 10%@100kHz? I've read that actually the faster you pwm the better because of thermal resistance. How much? I have no idea ;/ Last thing I want to do is create a system that burns up a 100$ worth of led's.
I've noticed with my led's that with low current but all LED's on that I can see the individual colors. They do not mix well to form white. But with higher currents I can a much better mix. I'm not sure if this is a defect in the specific led's or one of all RGB led's. It obviously has to do with how close the individual colors.
I guess the only thing for me to really do is run some tests. Was hoping someone else already did this(I'm sure someone has).
It is. Power is a big issue, for example. Distribution as well as dissipation. Even though it remains a broadly simple concept.
You asked earlier how to tell about power consumption other than with the LEDs. I hope you have the means to estimate that, now. It's not hard to estimate, but it is important.
It's challenging enough so that you ask some reasoned questions, though.
It is. Power is a big issue, for example. Distribution as well as dissipation. Even though it remains a broadly simple concept.
You asked earlier how to tell about power consumption other than with the LEDs. I hope you have the means to estimate that, now. It's not hard to estimate, but it is important.
It's challenging enough so that you ask some reasoned questions, though.
It was a very important issue in what I worked on. LEDs, even those picked from the same wafer, vary substantially in their appearances to humans. One project I worked on binning LEDs for display purposes exactly because of this problem. There was (and to my knowledge today, still is) a need for binning. Before the LEDs are placed into simple display systems like 7-segment units as well as in matrix LED systems. Another project was setting up a spectrophotometer system designed to calibrate RGB 16x16 display modules and provide basic calibration of the relative intensities of the three color system for proper white balance as well as dot correction. The white balance itself was very interesting and I found a unique solution that greatly eased the process and that hadn't been uncovered before for these purposes. I wrote a nice paper on the subject, a few years back.
I don't know your application, but you keep mentioning dot correction ("the biggest problem seems to be dot correction") and here above also say that it "will not be an issue... in any event." And this isn't the first time you brought it up. That duality of mind is confusing to me. My own experience here is that dot correction makes a difference -- people do "see" the difference it can make. Of course, you know your application. But I don't know why you keep bringing it up and knocking it down, again.
Is it an issue, or not? If not, drop it. If so, let's talk about it.
Why? Why not use it and a mux, too?
What, exactly?
Compared to what, exactly. I see the "simple drivers" page. But what is the expensive spread, here?
It would help to have a diagram. What I'm visualizing seems to be just fine and what you are visualizing seems not to be, to you. So we aren't thinking the same thing. Which means I may need a diagram to help me get synched up with your mind.
I'm imagining something working just fine with those one-channel per LED devices. I'm not sure why you see a problem with them. I actually like the one for which you provided a link, just fine. (I haven't used it, but it looks nice enough.)
No escaping that fact unless you locally store the settings for each pixel, yes?
It makes sense to me that it's better to go faster because the cooling/heating sawtooth of each LED (for a given PWM and drive current) submitted to muxing has smaller peak-to-peaks in it. I suspect the reason that is 'better' is because of the mechanical flexing caused by the heating/cooling is a 'bad thing' to be minimized. Of course, your dot clock (without local storage) will get ornery at some point.
Oh, cripes. I thought you wrote "not an rgb" in your first post on this subject. Now that idea is scrubbed. Back to RGB, again.
Matched white balance across am RGB panel requires some thought and work. I used to set this up at 25% peak current, by the way.
So what are you doing, again? And what are you using to establish a standard, here?
Yes. When very bright, you get a lot of internal reflections and diffusion that remain significant. Without that, you can see the die isolated. The RGB units I worked on had tiny LED dies carefully placed right next to each other. I could go look again (I still have a sack full) and see how close, exactly. But they were close. 3mm and 5mm spacing depending on the module, RGB to RGB centers, and the three LEDs occupied perhaps less than 1mm across all three. At very low currents, though, it was easier to see the individual LEDs. At
25% peak, it looked fine.
I have done some things you are looking to do, it seems. Not everything. But at least some of it. In the units I used, much like the chip you mentioned above, they used a separate multi-turn pot for setting the R, or G, or B peak current. To properly balance the three pots, I required a spectrophotometer with the right separation distance for optical work. I would have the operator simply set the pots to some rough midpoint (didn't matter, really) and I'd turn all of the RGB leds on at the same instant and take a spectrophotometer reading. This data (2000 linear pixels worth, calibrated itself using a standard lamp for intensity and a merc-argon lamp for wavelengths) would then be processed using CIE color curves (I can send these to you, if you like) and used to generate a matrix I'd use. The system would then continue to operate the spectrophotometer while the operator would then turn the R pot until a "ball" was centered on an image I drew for them (they'd turn it clockwise or counterclockwise, as appropriate, to center it) until I told them to stop, then turn the G pot, then turn the B pot. Actually, it didn't matter which they did first. Regardless, once they'd centered each, the panel was calibrated for white balance.
There was more, of course. Including dot correction. But that was later.
I still don't understand what you don't like about the chip you mentioned... what makes it difficult for you to consider using? (Other than it's low maximum current per LED, which seems a bit slight to me.) Why can't you consider using just one IC as part of a by-8 mux? That would be 16*8 or 128 LEDs with that one IC and something for muxing the anode side, of course. Shift in 16 bits, enable, disable, shift in 16 more bits, enable, disable, etc., while you work the anode mux side. I guess I'm not following why this is a problem.
Assuming your 24x19 is multiplied by 3 (RGB), this is four ICs per color, yes? So a total of 12?
Is this roughly in that 24:19 ratio, for use as panels placed together into a matrix ultimately for what amounts to a 4:3 RGB LED video display? You've now made me curious.
Yes, it could be an issue. The fewer the IC's the more each IC has to dissipate. It all depends on how much maximum current I use for each led and if I use a matrix or not. In am matrix the peak current per channel goes up times the number of rows. So the number of rows I use will depend on the ability for the drivers to drive them which still all depend on how much current I want to drive the led's with. 1mA means no problem. 20mA could mean disaster. The more rows for IC means less IC's which means cheaper. This is an optimization problem with a few kinks that I need to work out.
Yes,
The details are challenging because I have not done such a project before. The concepts and main idea are extremely simple. The issues are simple a matter of practicality. It setup as system and have it work is almost childs play. To design a system that is both cost effective and optimal in it's purpose is a totally different story.
.
No, I meant that it is with most applications but shouldn't be with mine. I do not know if it's an issue or not but because the led's will not be spaced closely I do nothing it will be. Again, practical matters make things more complex than they really should be. If the variance between LED's is more than 10% and those with the IC's are 5% then that could be a huge difference enough to make it cause problems with my application. Because to fix it requires one to have adequate PWM steps to counter it. If I were to have 5 steps then I might not be able to correct it. It's complex because it depends on so many unknown factors. I am trying to learn more about those unknown factors but seems no one has any specifics.
This is what I mean by a matrix. I didn't mean to use it above. But by a matrix I mean that the rows(or cols) are muxed. 1-ch per driver doesn't really have rows or cols even though you might lay them out in such a way each led has it's own cathode.
Again, I have said. The mux idea is cheaper but I cannot have onboard PWM. This is not a huge issue as I can do it in software assuming it does not interfere with the refresh rate causing the led to behave in weird ways. Which is the kinda info I am after. (see the end for more of a discussion)
Don't know. Most are 2-10 times the cost of the chip I gave below. I was thinking about the TLC5497. This is very simple application using this chip as it does almost everything internally but is much more expensive.
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Yes, it would work fine.... except for cost. It actually makes it easier to do as far as electronics is concerned(just connect the dots basically). Using the 16-ch drivers is pretty easy and being that they are cheap means overall it is cheaper. Unfortunately the only real problem I potentially see here is one of routing(I only have so much space and it's an awkward design). They do have I2C chips that would make it easier but are about 3x more expensive and I possibly could run into a comm speed issue.
Using a matrix with each IC driving several rows reduces the number of IC's. This reduces cost but adds to complexity and creates a whole set of new issues. Hence, since I am minimizing costs this seems like the best way... yet it creates many issues that might make it less cost effective or even an utter failure.
What would be nice would be a specific chip to drive large arrays. There are 16x8 drivers that can be cascaded which requires only about
4 of these
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TLC5920&fileType=3Dpdf
Those chips are about 2$ in large quantities. Hence, the cost per led is
.031 for the TLC59025 16-ch driver .1 for the TLC5947 for the 24-ch driver .023 for the TLC5920 128-ch driver
Not sure if the .7c is worth it but that is a savings of ~3$ overall and saves board space.
Unless I do not drive them in a grid.
I am essentially doing a panel of LED's that are not close at al. Maybe an inch apart. The LED's will communicate information to the user (that is all you have to know ;). I know it might seem a bit wierd but trust me that it is a project and maybe one day you'll "get" what I'm doing.
I believe I can do all this using "dot correction". If I have enough headroom and and enough PWM steps I can simply run the board through spectrophotometer or even a simple camera and reduce the intensity's as necessary. In fact I could generate a profile for each individual LED, all automatically, and store it in the main controller and simply map the PWM data to it to counter the differences. This is assuming the differences are constant and independent of temperature(which I could even try to compensate for).
In any case the application is not that critical that it will be ruined for slight differences.
There are three reasons about the chip. One is cost but not so big since it's the cheapest 16-ch driver I could find. Second is the number of IC's. I would like to get this onto a 2-layer board if possible. This is a routing issue mainly. Thirdly is that it does not support PWM which I have to implement externally. If I wish to change only one led, and I cascade multiple drivers to reduce the IO lines to the board, then it requires a fast data transmission. Faster clock may cause problems as I want a simple comm.
I have seen some I2C drivers, as I think I mentioned, which would work well if they were SPI and actually cheaper. Really what I need is a very good IC that does everything I need ;) Of course then my cost goes up making that choice more questionable.
I might just bite the bullet on the cost and go with 24-ch ones as I have done most of my research and mocked up a circuit for it. I'm just having a problem stomaching the cost when I know it can be done much cheaper with similar capabilities.
No, I have taken into account the rgb's.
I can use the mux idea. It requires fets for each row that shouldn't be a problem. But if I go this way I have to worry about exceeding the electrical characteristics of the IC and LED's.
Assuming 8 rows per driver. For the 16-ch driver that is 128 channels. This is very similar to the 128-ch driver but cheaper but requires external common's. Not that big a deal as I can tie them all together assuming my row switching is not too expensive.
The problem with the 16-ch drivers is that muxing them will quickly go out of spec. 1 LED draws 10mA then with 8 rows causes the peak current to be 80mA... or almost twice that of rated. At max I could drive 2 or maybe 3 rows with this chip. There are better chips out there, of course, but at a higher cost. Also because I have fewer rows it requires more IC's which increase cost.
So while the muxing idea looks good on paper it does not at all work. The IC just can't handle the current needed. Of course even if I had only 2 rows it means I've reduced the cost by a factor of 2. Instead of about 30 chips I would need 15.
It would be nice if they had a chip that had PWM that worked for muxing. That is, you could change the PWM for each row when you changed rows. It would be very simple to implement and make life so much easier. If I use mux it is useless to use PWM IC's. If I use mux then I need an IC that can handle the capacity that is no so expensive for me not to use mux.
Surely you see the conundrum? To mux or not to mux, that is the question! ;)
BTW, one other constraint is the chip size. I would like to use the smallest package available except for BGA. That 59025 is in ssop but the 5947 is a QFN which is pretty nice.
One other thing. If cost was not an option and everything else being the same then I would go with the 5947. If the 59025 was in QFN and had PWM and cost was the same(50c) then I would go with that. The package type is for mechanical and layout reasons. The PWM is a nice feature but not actually necessary but makes life a bit easier. Remember, I can't mux and use internal PWM so I have to find the best chip for the job.
It is amazing how many people are desperate to believe that pulsating a light source produces some majical effect in the eye and perception is enhanced. The effects of 'flicker' are well known and have been documented for a very long time now - having been rigorously studied in a scientific manner by several well known authorities.
Miso is a major proponent of the magic of modulating a lightsource to improve its perseption in SED - I suspect he did something using the magic principal and has been desperate to gain some credence for it ever since.
Just have a look for the work of Brocker, Sulza, Talbot, etc - *any* decent website dealing in vision will reveal all.
Well, probably because there is some truth mixed into the lie. Human perception has many remarkable features.
The sense of color perception is an example where studies made in the early 1900's lead to the 1931 CIE color standards (revised in 1964.) Edwin Land's remarkable studies in the late 1970's and early 1980's brought whole new aspects to the question, demonstrating (in part) a few interesting ideas: for example, that although there is a dramatic shift in the distribution of emitted wavelengths by a tungsten filament as it is dimmed and brightened as a light source, a stretched canvas containing myriad color swatches had their colors easily discerned by observers despite the radical changes in lighting... but that if a drape with a hole in it were placed over the surrounding colors that perception was lost and behaved far more as one would expect from the reflected wavelengths. In other words, color perception includes information from surrounding areas, as well, in order to develop the fuller sense.
And of course most everyone is aware of some of the many "optical illusions" that abound.
So it's easy to accept the idea about 'peak response,' otherwise ignorant. I don't fault anyone for getting it wrong. It's just, as you say later, that there is abundant evidence to the contrary if one either reads the work of others or else performs a few simple experiments of their own.
On that latter point, I'm reminded of Galileo's comment within The Assayer. It is well worth reading from beginning to end, but here is a snippet from Stillman Drake's translation. In it, Galileo is responding to Grassi (writing under the pseudonym of 'Sarsi') and the adherence to the idea that the Earth is surrounded by a sphere of fire and that when objects rise up into the sky they get close to this sphere and can burst into fire in response:
"... But it is wrong to say, as Sarsi does, that Guiducci and I would laugh and joke at the experiences adduced by Aristotle. We merely do not believe that a cold arrow shot from a bow can take fire in the air; rather, we think that if an arrow were shot when afire, it would cool down more quickly than it would if it were held still. This is not derision; it is simply the statement of our opinion.
"Sarsi goes on to say that since this experience of Aristotle's has failed to convince us, many other great men also have written things of the same sort. To this I reply that if in order to refute Aristotle's statement we are obliged to represent that no other men have believed it, then nobody on earth can ever refute it, since nothing can make those who have believed it not believe it. But it is news to me that any man would actually put the testimony of writers ahead of what experience shows him. To adduce more witnesses serves no purpose, Sarsi, for we have never denied that such things have been written and believed. We did say they are false, but so far as authority is concerned yours alone is as effective as an army's in rendering the events true or false. You take your stand on the authority of many poets against our experiments. I reply that if those poets could be present at our experiments they would change their views, and without disgrace they could say they had been writing hyperbolically -- or even admit they had been wrong.
"Well, if we cannot have the presence of your poets (who, as I say, would yield to experience), we do have at hand archers and catapultists, and you may see for yourself whether citing your authorities to them can strengthen their arms to such an extent that the arrows they shoot and the lead balls they hurl will take fire and melt in the air. In that way you will be able to find out just how much force human authority has upon the facts of Nature, which remains deaf and inexorable to our wishes. You say there is no longer an Acestes or a Mezentius or other mighty paladin? I shall be content to have you shoot an arrow not with a simple longbow, but with the stoutest steel crossbow, or use a catapult drawn by levers and windlasses that could not be managed by thirty of your ancient heroes. Shoot ten arrows, or a hundred, and if it ever happens that on one of them the feathers so much as slightly tan -- let alone its shaft taking fire or its steel tip melting -- I shall not only concede the argument but forfeit your respect, which I regard so highly..."
Nature doesn't care a whit about human opinion, wish, fantasy, or authority -- it does what it does, consistently, and without recourse to human desire about it. But also, without disgrace, we can admit our errors in the face of contrary experiment. In other words, it's not a disgrace to lose ignorance and become informed by experimental result.
The Assayer is interesting to read, in hindsight.
I must have missed that.
Yes, the Talbot-Plateau law. But there are some 'effects' at low blinking rates, below the critical fusion frequency (which varies by area of stimulus as well as whether scotopic or photopic dominates.)
The one thing I remember was the value of 70Hz as the photopic figure. In my own experiments here, with a small green LED, I found that about
45Hz fused it (age: 50 years) if I didn't move at all, but that for modest ranges of motion I needed closer to 60Hz to fuse it well. All this goes to the point that 70Hz is probably a good top end benchmark for still objects. Under vibration, I'd insist on a still higher modulation frequency.
Well, yes. It's possible that an observation like that might have stimulated some thoughts about fire. However, Aristotle goes at great length in Book I about his ideas. So we really don't need to guess. He struggles with a question he poses about "the intervals" in the "upper region" and writes,
"If the intervals were full of fire and the bodies consisted of fire every one of the other elements would long ago have vanished. However, they cannot simply be said to be full of air either; for even if there were two elements to fill the space between the earth and the heavens, the air would far exceed the quantitu required to maintain its proper proportion to the other elements."
He begins his conclusion like this,
"But whenever a particle of air grows heavy, the warmth in it is squeezed out into the upper region and it sinks, and other particles in turn are carried up together with the fiery exhalation. Thus the one region is always full of air and the other of fire, and each of them is perpetually in a state of change."
Here, he is clearly NOT arguing from the perspective of meteors. In fact, he doesn't even bring them up. Though I suppose they may have played a role inspiring his direction of thought.
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