Fluorescents and migraines??

On Sun, 13 Jan 2008 19:11:30 +0200, "I.N. Galidakis"


Yes - at least for me. I can measure significant 120 Hz on the light output of all the the CFLs in my house, but I don't see any flicker.
--
Vic Roberts
http://www.RobertsResearchInc.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Victor Roberts wrote:

[snip]
Thanks Vic. That was a sanity check for me. I actually unpacked my PHILIPS SL-18W, which is the oldest one I've got (1982 or thereabouts) and I asked an array of visitors if they could see any flicker and they said no.
Although the SL-18W uses a magnetic ballast, I believe that the triphosphor phosphor persistence is so great that it drowns any visible flickering.
One my newer types there isn't even a question as they use electronic ballasts.
So I was wondering what on earth was all the fuss about.
--
I.N. Galidakis


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| Victor Roberts wrote: |> On Sun, 13 Jan 2008 19:11:30 +0200, "I.N. Galidakis"
| [snip] | |>> Are we talking about non-perceptible flicker? |> |> Yes - at least for me. I can measure significant 120 Hz on |> the light output of all the the CFLs in my house, but I |> don't see any flicker. | | Thanks Vic. That was a sanity check for me. I actually unpacked my PHILIPS | SL-18W, which is the oldest one I've got (1982 or thereabouts) and I asked an | array of visitors if they could see any flicker and they said no. | | Although the SL-18W uses a magnetic ballast, I believe that the triphosphor | phosphor persistence is so great that it drowns any visible flickering. | | One my newer types there isn't even a question as they use electronic ballasts.
And just how is it that electronic ballasts imply there can be no flicker? Sure, if they completely and totally smooth out the power to pure DC, then there would likely be no flicker (assuming they don't chop that DC at some too low frequency). But merely chopping alone still leaves very little power at zero crossovers. I had suggested harmonic chopping such that the flicker rate would be 2 or 3 times as high. But that would really make some awful power factor.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@ipal.net wrote: [snip]

Quoting from Wikipedia (section flicker):
http://en.wikipedia.org/wiki/Fluorescent_lamp
"Both the annoying hum and flicker are eliminated in lamps which use a high-frequency electronic ballast, such as the increasingly popular compact fluorescent bulb."
and later down:
"Electronic ballasts do not produce light flicker, since the phosphor persistence is longer than a half cycle of the higher operation frequency.
The non-visible 100120 Hz flicker from fluorescent tubes powered by magnetic ballasts is associated with headaches and eyestrain."
I guess the confusion arises from the distinction between "perceptible/non-perceptible" flicker.
If you actually "perceive" non-perceptible flicker, then I guess you belong in that special population sample, which is an exception.
I do find it highly suspicious however, that such an issue was never raised 20-30 years ago, when most of the fluorescent lamp population was powered by magnetic ballasts, which had a PERCEPTIBLE flicker.
How come nobody had headaches back then?
Or did they?
Well, if they did, _I_ never heard anything about it back then.

--
I.N. Galidakis


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I did hear about it.
Also, electronic ballasts mostly have imperfect smoothing of the DC, and have slight 10/120 Hz flicker.
However, I do suspect that a majority of the "ill effects" are psychosomatic. Given the abundance of health claims of particular spectral power distributions and lack of sellers of "healthier fluorescent fixtures" with ballasts having a DC voltage regulation stage after rectifying the incoming AC, I have a dim view of claims of ill health effects until confirmed by good double-blind trials. And by double-blind, I mean anyone involved wearing eyeglasses wearing achromatic ones. Along with fluorescent lamps being studied as well as incandescent controls being in fixtures that do a good job of hiding the lamp type - including, if necessary, filter gels (put them in all fixtures if they are detectable to maintain double-blindness) to make fluorescents and incandescent controls have the same color.
I am also suspicious of claims of flicker-related ill effects of fluorescent lighting that are not also triggered by CRT televisions and CRT computer monitors. Many people think CRTs have some bigtime phosphor persistence, and I did some high speed photography of my CRT monitor and my CRT TV to have phosphor persistence of only a millisecond or two, and my monitor to have phosphor persistence even less, about a millisecond.
My monitor sure looks fine to me at 100 Hz. I think it's 100 - that is the maximum option, and what I had was "optimal". I change it to 72 Hz and I get no perceptible flicker, but sometimes I get "sensatuion it's flickering" - maybe psychosomatic. I find this fixed almost halfway at 75 Hz. I see only minor change from 75 to 85 Hz - several seconds later it looks "pretty much OK" after all. I try 90 Hz and everything looks and feels fine and good.
I am about to try 100 Hz specifically - will followup soon if I dont blow up my $40 monitor in the next few minutes! (I have a spare monitor handy)
- Don Klipstein ( snipped-for-privacy@misty.com)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Now I have it at 100 Hz, and I "felt" some slight improvement over 90 Hz. It may be psychosomatic. But I stare into a corner of the monitor from 3 inches (75-80 mm) away when set to 85 or 90 or 100 Hz, and those all feel the same to me. OK, 85 gives me a slight "nervous feeling" when I do this, but I suspect that's psychosomatic, especially since 75 at this moment "feels only slightly worse" than 85 does. (I am currently changing vertical scan frequencies downward and spend several seconds staring into the lower left corner of the display from about 3 inches away.)
70 Hz gives me a slight visible flicker perception that 75 does not. I got only slightly worse "nervous sensation" at 70 Hz than at 75. Changing from 70 to 72 Hz removes the perceptible flicker.
Changing this to 60 Hz makes my monitor appear very flickery at this moment, though I know that in the past I have gotten used to 60 Hz monitor flicker. CRT televisions in the USA use 60 Hz vertical scan rate.
56 Hz only looks a little worse to me now than 60 does. However, I do remember times in the past when I mostly saw a monitor at 60 Hz to hardly visibly flicker or avoid visible flicker (maybe usually barely), while I almost always saw monitors to flicker at 56 Hz.
I now just changed my vertical scan rate to "optimal", which I think is 100 Hz but I can't rule out 85 or 90. I have a neon glow lamp next to the monitor and I look at both from a distance and roll my eyes up and down, and I can only say that my vertical scan rate now is less than 120 Hz but by a margin too small for it to be 75 Hz.
My TV, at 60 Hz, also has visible flicker of steady solid white areas when I view those at very close range. However, I mostly find that hidden by usually things on the TV moving, and also by details that have 30 Hz flicker if I look from only a few inches away.
In comparison, the flicker rate on non-malfunctioning fluorescent lamps is 100 Hz in Europe and 120 Hz in North America. (Excluding looking at and concentrating on the area around one end of the bulb if the ballast output is power-line-frequency AC, and that is not the case with electronic ballasts.)
I am now finding 60 Hz flicker (from a torchiere "lamp" with E-27 sockets and diode-dimmed and "full blast" settings) to be visible if I look at the luminaire, and to not be visible if I look at illuminated surfaces in the room. I find this from both incandescents and electronically-ballasted CFLs - 60 Hz flicker visible only if I look at the lamp or the luminaire, and 120 Hz having yet to be visible or giving me any noticed sensation, even psychosomatic.
- Don Klipstein ( snipped-for-privacy@misty.com)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 16 Jan 2008 06:08:11 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

Does the flicker show up more for you in peripheral vision?
Old monitors operating below about 75 Hz used to bother me, now I seem not to notice.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I see the flicker more in my peripheral vision and less in my central vision. The results I reported were with my eyes so close to the monitor that I was using both peripheral and central vision.
- Don Klipstein ( snipped-for-privacy@misty.com)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| Now I have it at 100 Hz, and I "felt" some slight improvement over 90 | Hz. It may be psychosomatic. But I stare into a corner of the monitor | from 3 inches (75-80 mm) away when set to 85 or 90 or 100 Hz, and those | all feel the same to me. OK, 85 gives me a slight "nervous feeling" when | I do this, but I suspect that's psychosomatic, especially since 75 at this | moment "feels only slightly worse" than 85 does. (I am currently changing | vertical scan frequencies downward and spend several seconds staring into | the lower left corner of the display from about 3 inches away.)
I believe the perception will vary depending on how much of the screen is exposed. Cover it up so only the top 10% lets light reach you and it may seem worse. Remember that it scans, so you get continuous light down to the point where it retraces back to the top.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| I am also suspicious of claims of flicker-related ill effects of | fluorescent lighting that are not also triggered by CRT televisions and | CRT computer monitors. Many people think CRTs have some bigtime phosphor | persistence, and I did some high speed photography of my CRT monitor and | my CRT TV to have phosphor persistence of only a millisecond or two, and | my monitor to have phosphor persistence even less, about a millisecond.
One difference about the CRT is that even though the persistence is short and the flicker effect can be high, it has that effect spread out in both geometry and time. That is, the aggregate light from the screen, not a single spot on the screen, has less flicker.
I found that flicker bothered me, but did not cause a headache (rather, it was more of a distraction), with CRTs. Above about 85 Hz it did not bother me, yet I could still see it. Now I have an LCD, and it has very little flicker (I can detect a tiny bit if I work at it).
I do see a bit more color spectrum issue with the LCD than with the CRT. My LCD at work (Acer) seems to be better than the one at home (LG).
| My monitor sure looks fine to me at 100 Hz. I think it's 100 - that is | the maximum option, and what I had was "optimal". I change it to 72 Hz | and I get no perceptible flicker, but sometimes I get "sensatuion it's | flickering" - maybe psychosomatic. I find this fixed almost halfway at 75 | Hz. I see only minor change from 75 to 85 Hz - several seconds later it | looks "pretty much OK" after all. I try 90 Hz and everything looks | and feels fine and good.
Looks like about that same 85 Hz range for both of us.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| snipped-for-privacy@ipal.net wrote: | [snip] | |> And just how is it that electronic ballasts imply there can be no |> flicker? | | Quoting from Wikipedia (section flicker): | | http://en.wikipedia.org/wiki/Fluorescent_lamp | | "Both the annoying hum and flicker are eliminated in lamps which use a | high-frequency electronic ballast, such as the increasingly popular compact | fluorescent bulb."
Don't believe what you read in Wikipedia, unless they get lucky and have something correct (it happens often, but not in this case).
The purpose of the ballast is to limit the current flow to prevent the negative resistance effect of the gaseous bulb from being a short circuit. Magnetic ballasts do this with an inductor in series. The inductor limits the current flow without wasting a lot of heat. A resistor could do so, too, but it would dissipate a large amount of heat and make things worse than an incandescent bulb. Actually, a capacitor could also do the job, but it would require a big one and is entirely not practical at 60 Hz.
The electronic ballast limits the current flow by turning the power on and off, usually at a very high frequency rate, with just enoug on times to prevent excessive current flow. A small capacitor can then smooth out current between those pulses. One way to do this is just to do the high frequency chopping directly on the AC. That little capacitor would not smooth across zero crossovers, so the light still gets little to no power during zero crossover, and this leaves the AC flicker there. The other way is to convert the AC to DC, smooth out the DC, and chop the DC itself at the very high frequency rate. No flicker because the smoothing of the DC removed it. The trouble is, this is more expensive. It is more practical do use this kind of ballast in a fluorescent fixture. But a CFL requires a cheaper more compact ballast, and a smooth DC type would raise the costs quite a bit.
| and later down: | | "Electronic ballasts do not produce light flicker, since the phosphor | persistence is longer than a half cycle of the higher operation frequency.
They do not _produce_ it. They may let it pass through by not storing any energy to "cover" the zero-crossover time period.
Magnetic ballasts do not _produce_ flicker either.
| The non-visible 100?120 Hz flicker from fluorescent tubes powered by magnetic | ballasts is associated with headaches and eyestrain."
Some people _can_ see it. Some people need to roll their eyes to see that it is there. Some people can just see it directly. It seems most people cannot see it either way.
| I guess the confusion arises from the distinction between | "perceptible/non-perceptible" flicker.
That is a point of confusion, sure. People are different. I see the flicker, but I have found that the flicker is not the cause if headaches I get under such lighting. I've gotten them with battery DC powered fluorescent lights.
| If you actually "perceive" non-perceptible flicker, then I guess you belong in | that special population sample, which is an exception.
Yep.
| I do find it highly suspicious however, that such an issue was never raised | 20-30 years ago, when most of the fluorescent lamp population was powered by | magnetic ballasts, which had a PERCEPTIBLE flicker.
It was raised. It was ignored mostly because people could use incandescent lights without any government intrusion. It is raised to a higher level now because the government wants to stop the sale of the incandescent bulbs.
Don't worry, we _will_ stock up in high numbers. Bulbs will be available on EBay and the black market ... for a price.
| How come nobody had headaches back then? | | Or did they?
I did! I just misunderstood exactly why. Back then I thought it was _because_ of the flicker. Now I understand it is because of the spectrum.
| Well, if they did, _I_ never heard anything about it back then.
You mean in the pre-internet days?
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@ipal.net wrote: [snip]

[snip ballast explanation for brevity]
Do I look to you like I need a tutorial on what is a ballast? If that's the impression I gave you, either my exposition powers are weak or your comprehension abilities are not up to par.

Wikipedia is not an engineering manual. For the lay person their explanation is correct. There is no point in arguing insignificant minutae with me (or with Wikipedia). /Of course/ ballasts do not "produce" flicker (literally), since they are not the main power supply which drives the lamp. But from a non-technical standpoint, it's the inductive resistance of the ballast which allows the AC cycle to propagate FROM the AC source to the lamp almost unchanged, making it seem as "flicker", for whatever reason, whether it be insufficient attenuation of the AC signal, bad power factor, "flattening" of the AC signal, lack of capacitors or whatever have you.
What really matters here is what Wiki says later, which you conveniently did not address:
"Electronic ballasts do not produce light flicker, since the phosphor persistence is longer than a half cycle of the higher operation frequency."
As far as I am concerned, THAT's the crucial point which proves there's no flicker.
Of course, if you say that you see flicker, there's no way for me to convince you otherwise. If I claim that yesterday I saw a grand pink elephant nest with green eggs and ham sitting at the center of a primordial black hole, there's no way for you to prove me wrong either.

I am not talking about whether one can see it by rolling one's eyes back and forth. I can see flickering even on incandescent sources if I roll my eyes back and forth. The question is whether a lay person can perceive consciously 100-120 Hz flicker without doing a circus act with one's eyeballs. THAT's the question.
It's a question of whether the perceptual system "eye-brain" has the capacity to perceive this flicker on standing mode ON A CONSCIOUS LEVEL and whether this flicker can cause headaches.
I am ready to agree that although the flicker itself may not be /visible/ on a CONSCIOUS (PERCEPTUAL) LEVEL, the brain may be able to pick it up subconsciously. That's a contention I am ready to argue about, as a potential source of migranes. The rest is irrelevant.
[snip]

Huh? How can you be sure without knowing the EXACT cause of what bothers you in the spectrum?
Or if you DO know the exact cause, what is it that bothers you in the spectrum?

--
I.N. Galidakis


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| snipped-for-privacy@ipal.net wrote: | [snip] | |> Don't believe what you read in Wikipedia, unless they get lucky and |> have something correct (it happens often, but not in this case). |> |> The purpose of the ballast is... | | [snip ballast explanation for brevity] | | Do I look to you like I need a tutorial on what is a ballast? If that's the | impression I gave you, either my exposition powers are weak or your | comprehension abilities are not up to par.
I've looked at lots of people, and I've never found any real easy means to determine from their appearance, mannerisms, hygiene, or other aspects, whether then need a tutorial on what a ballast is, or not. That, and I didn't even look at you at all, since this is the Internet. So it's just a crapshoot. But you were looking in Wikipedia for information. That is enough to make me worry.
|>> and later down: |>> |>> "Electronic ballasts do not produce light flicker, since the phosphor |>> persistence is longer than a half cycle of the higher operation |>> frequency. |> |> They do not _produce_ it. They may let it pass through by not |> storing any energy to "cover" the zero-crossover time period. |> |> Magnetic ballasts do not _produce_ flicker either. | | Wikipedia is not an engineering manual. For the lay person their explanation is | correct. There is no point in arguing insignificant minutae with me (or with | Wikipedia). /Of course/ ballasts do not "produce" flicker (literally), since | they are not the main power supply which drives the lamp. But from a | non-technical standpoint, it's the inductive resistance of the ballast which | allows the AC cycle to propagate FROM the AC source to the lamp almost | unchanged, making it seem as "flicker", for whatever reason, whether it be | insufficient attenuation of the AC signal, bad power factor, "flattening" of the | AC signal, lack of capacitors or whatever have you.
The resistance in the inductor has nothing to do with it. Maybe you meant to say "impedance" instead of "resistance".
Using the correct terms can, in quite many cases, be very crucial. If you want to be an engineer (even if you just want to play an arm-chair engineer on the Internet), learn to use the correct terms. I had to.
If you want to simplify things, or even over-simplify things, that's one thing. But when things just get wrong, that gives me cause for concern. I've had to deal with (in my field, computer software) people who too often take something that was a simplification as being something of detail and ended up with an entirely wrong understanding. I not saying you have misunderstood these technical things; I'm concerned more about what others might read from Wikipedia or your quotations.
| What really matters here is what Wiki says later, which you conveniently did not | address: | | "Electronic ballasts do not produce light flicker, since the phosphor | persistence is longer than a half cycle of the higher operation frequency." | | As far as I am concerned, THAT's the crucial point which proves there's no | flicker.
Still, that is incorrect.
That statement from Wikipedia suggests that it is the persistence of the phosphor that makes the electronic ballast not produce flicker. That is not just wrong, it's even silly.
Phosphor persistence can help reduce flicker. In very extreme cases it could even eliminate it, in theory (but expect the light to continue to glow for a very long time after you turn it off). This effect would be the same whether the lamp current was being limited by an inductive ballast, capacitive ballast, resistive ballast (no one would use such a beast, but one could be made), or an electronic solid-state ballast.
Try this statement on for size:
"Magnetic ballasts do not produce light flicker, since the phosphor persistence is longer than a half cycle of the higher operation frequency."
Is that any more or less "correct" in the context of Wikipedian engineering than what you quoted from there?
| Of course, if you say that you see flicker, there's no way for me to convince | you otherwise. If I claim that yesterday I saw a grand pink elephant nest with | green eggs and ham sitting at the center of a primordial black hole, there's no | way for you to prove me wrong either.
There are a lot of things I see in a lot of aspects of the world that a lot of people try to convince me is not really there. THEY don't see it, so as far as they are concerned, it really isn't there. I hope you are not slipping into that category.
I wouldn't even try to prove you wrong on your sighting, even though I am quite certain that black holes have no center.
|>> The non-visible 100?120 Hz flicker from fluorescent tubes powered by |>> magnetic ballasts is associated with headaches and eyestrain." |> |> Some people _can_ see it. Some people need to roll their eyes to see |> that it is there. Some people can just see it directly. It seems |> most people cannot see it either way. | | I am not talking about whether one can see it by rolling one's eyes back and | forth. I can see flickering even on incandescent sources if I roll my eyes back | and forth. The question is whether a lay person can perceive consciously 100-120 | Hz flicker without doing a circus act with one's eyeballs. THAT's the question.
And I can see the flicker directly. I just can't see very accurately how MUCH there is, or how much of it is compensated by the phosphors. When I do scan my eyes across, I can see things that give me more information. If the light is literally on and off that tells me one thing. If the light descends into a different color, that tells me another (phosphor persistence is usually variant in color in fluorescent lighting ... the totally color you get is the average over time).
| It's a question of whether the perceptual system "eye-brain" has the capacity to | perceive this flicker on standing mode ON A CONSCIOUS LEVEL and whether this | flicker can cause headaches.
I can see the flicker from most fluorescent lights even when only viewing the reflection of it from broad surfaces.
However, I have found that this does NOT cause headaches for me. I cannot say if it does or does not cause it for others. I used to THINK that the flicker was the cause, basically because it had been suggested for decades.
| I am ready to agree that although the flicker itself may not be /visible/ on a | CONSCIOUS (PERCEPTUAL) LEVEL, the brain may be able to pick it up | subconsciously. That's a contention I am ready to argue about, as a potential | source of migranes. The rest is irrelevant.
I certainly cannot just count the 120 pulses per second. I can see that it is flickering, but I cannot see individual pulses happening. I do not see it as going on and off. I see the sense of flicker. I see it in some LEDs but not in others. The ones that are battery powered don't have the flicker. Yet they can cause the headaches.
|>> How come nobody had headaches back then? |>> |>> Or did they? |> |> I did! I just misunderstood exactly why. Back then I thought it was |> _because_ of the flicker. Now I understand it is because of the |> spectrum. | | Huh? How can you be sure without knowing the EXACT cause of what bothers you in | the spectrum? | | Or if you DO know the exact cause, what is it that bothers you in the spectrum?
The spectrum is not continuous. It has a large gap or two large gaps in it. My eyes do not focus all colors at an equal distance. Glasses exacerbate that problem (more so at the edges of the glass). As a result, the edges where light is different, such as the edge of black text on a white page, is not in perfect focus. With a smooth continuous spectrum, it will appear to be slightly fuzzy, but tolerable. With a broken spectrum, there will appear to be 2 or more distinct edges. In the latter case, my eyes are constantly jumping back and forth trying to focus in one color or the other. That constant refocusing creates stress, and eventually a headache. This is what appears to be going on for me. I do not know if others have the this kind of issue or not. I do not know if they can get headaches from other things that don't affect me. I've learned that people are sufficiently different to never make such assumptions (although I've met many people that have not learned that for themselves).
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 16 Jan 2008 15:43:11 GMT, snipped-for-privacy@ipal.net wrote:

You are assuming an ALL or NOTHING situation. All CFL ballasts I have seen have a DC storage capacitor and therefore smooth the DC link voltage to some extent. They just do not have a large enough capacitor to completely eliminate the 120 Hz ripple. In fact, many CFL ballasts have about 50% ripple on the DC link.

Of course they "produce" it.
--
Vic Roberts
http://www.RobertsResearchInc.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| You are assuming an ALL or NOTHING situation. All CFL | ballasts I have seen have a DC storage capacitor and | therefore smooth the DC link voltage to some extent. They | just do not have a large enough capacitor to completely | eliminate the 120 Hz ripple. In fact, many CFL ballasts | have about 50% ripple on the DC link.
That must be what I am seeing, then. | | |>| and later down: |>| |>| "Electronic ballasts do not produce light flicker, since the phosphor |>| persistence is longer than a half cycle of the higher operation frequency. |> |>They do not _produce_ it. They may let it pass through by not storing any |>energy to "cover" the zero-crossover time period. | | Of course they "produce" it.
How is it that ballasts of any kind "produce" flicker?
Actually, I think I might have an example. I have seen many cars with rear tail lights, red in color, that are flickering. If they are powered via the battery, why would that be? I presume they are LED, so there is no reason for a voltage boost that might involve an AC circuit or at least some kind of pulsing DC. I am suspecting the pulses come from either a current limiter meant to reduce energy loss through dissipation (e.g. not using a resistor), or an intensity modulation (in some of the cards, the flickering stops when the break lights come on, bringing the same LEDs up to full intensity). So that may well be a case of a "ballast" producing the flicker. In the case of an AC powered fluorescent light, maybe it is "producing" a 30 kHz flicker?
That flicker on the highway is somewhat annoying _because_ I have to move my eyes around a lot to constantly check many vehicles. It does NOT cause headaches (although some of the drivers out there do).
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes I've noticed that effect to, I find it really strange.
It seems Ok if I look full at them but if they are moving across my line of vision or my eyes are scanning round then I see it.

Most certainly.

Possibly
I have mentioned this to others on occasions but they seem not to have seen the phenomena
--
Stuart Winsor

From is valid but subject to change without notice if it gets spammed.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 15 Jan 2008 20:55:34 +0200, "I.N. Galidakis"

I think the confusion arises because people assume that there is no modulation of high frequency output. These are people who don't understand how an electronic ballast really works. They have never thought about the fact that the high frequency oscillator is powered by an imperfect DC power supply.
--
Vic Roberts
http://www.RobertsResearchInc.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Victor Roberts wrote: [snip]

and also in another post:

Let me see if I can use the above to demonstrate mathematically that there exists at least one kind of CFL which does not flicker.
Count the original oscillator in both the above cases as ONE, and the video FPS rate as TWO. Vic, above, effectively says that we always have _some_ ripple even in the best possible cases and hence some light flicker. Therefore, when we video any (even so slightly) flickering light source, we effectively have two coupled oscillators, so the effects can be analyzed mathematically.
It turns out that the slower oscillator (which in this case is the video) "captures" the behavior of the fastest one:
http://ioannis.virtualcomposer2000.com/math/video.html
For those who wish to forgo with the math, the above simply means that:
"If there's light oscillation, then it shows on video. Hence, if nothing shows on video, there's no light oscillation".
If, without loss of generality we try the above analysis for some ridiculously high value of light oscillation, say 67361 Hz or 67.3 kHz, the resulting Diophantine equation gives:
k3680+67361*n j@+80*n.
Let's pick j, which is easier. The first "flickering" ripple on the video should occur at 2*(40+80)/80 secs = 3 secs. The second flickering ripple on the video should occur at 2*(40+80*2)/80=5 secs. This means that if the light was oscillating at 67.361kHz, the video would have shown flickering ripples with a time amplitude of 2 seconds.
Since the video of the CFL is much longer than 2-3 seconds, it follows that a high light oscillating frequency at least up to 67.361 kHz is not likely.
Adjust the equation per your preferences, adding mayo and jalapeno peppers. I suppose I could solve the problem backwards and try to find what is the maximum oscillation frequency whose video ripple amplitude is larger than a minute worth of video, but it's a little late now and I need to pass to the other dimension for some rest.
(Sorry about having the videos on QuickTime format, but that's my camera's capture mode and as I said, I am a little tired right now. For those who don't know about it, QuickTime is a free download from Apple).
Anyone who disagrees with the above conclusion, please raise your hand... ;o)
--
I.N. Galidakis


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 17 Jan 2008 03:18:19 +0200, "I.N. Galidakis"

I raise my hand in objection.
Instead of your complicated arrangement I just connect an optical detector to my oscilloscope and point it at a CFL. If the trace on the oscilloscope shows modulation, then the CFL light output is modulated.
I've attached a trace of a CFL with small amount of 120 modulation of the light output. The zero level is about 1 division from the bottom of the screen, at the arrow marker.
--
Vic Roberts
http://www.RobertsResearchInc.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 16 Jan 2008 22:33:30 -0500, Victor Roberts

The attachment failed. I posted another message with a link to a BMP of the scope trace.
--
Vic Roberts
http://www.RobertsResearchInc.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.