Flicker in CFLs, linear fluorescent lamps and LEDs.

[Victor Roberts]

It is generally known that fluorescent lamps operated on
line frequency EM ballasts produce a substantial amount of
flicker at twice the power line frequency: 100 Hz or 120 Hz
depending upon country. This flicker is known to cause
create headaches in some people.

The conventional wisdom is that fluorescent lamps operated
on high frequency fluorescent ballasts will not create
headaches. The phosphor cannot respond to variations in UV
intensity at frequencies of 20 kHz and above, and the small
amount of light emitted directly by the mercury will be
modulated at frequencies far too high to be detected by the
eye/brain system.

However, after receiving a number of questions about
electronically ballasted CFL's and headaches from Ira
Krepchin of E Source, I ran a short series of experiments
and have concluded that the conventional wisdom may be
wrong.

Electronic ballasts for both linear and compact fluorescent
lamps, along with drivers for LEDs, almost always operate
from 50 Hz or 60 Hz single phase AC power sources. The AC
power is rectified to make DC power using a full-wave bridge
or perhaps a voltage doubler. The DC power is then used to
operate a high frequency inverter that, in turn, drives the
fluorescent lamp. (For an LED the DC power is used to with
a current regulator to drive the LED.)

The DC power produced by such a full-wave bridge will be
100% modulated at twice the power line frequency. If the
DC power source is modulated at 100 Hz or 120 Hz, the high
frequency power produced by the inverter will likewise be
amplitude modulated at 100 or 120 Hz. The extent of the
modulation of the high frequency power will be dependent on
the design of the inverter, but many inverter designs will
produce approximately the same percentage of 100 Hz or 120
Hz modulation on the high frequency power as exists on the
DC power supply. No practical inverter can produce a
non-modulated high frequency signal from a DC power source
that has 100% 100 Hz or 120 Hz modulation.

To reduce the modulation of the DC power supply in the
ballast an energy storage device, typically an electrolytic
capacitor, is connected to the output of the rectifier.
However, due to cost and size constraints, plus the fact
that the addition of this energy storage capacitor creates
low input power factor, the value of the capacitor used is
large enough to eliminate much of but not all of the 100 Hz
or 120 Hz modulation of the ballast's DC power source.

The result of this DC power modulation is that the high
frequency power generated by a typical high frequency
fluorescent lamp ballast can have a substantial amount of
100 Hz or 120 Hz amplitude modulation superimposed on the
high frequency power used to drive the lamp. This
modulation, in turn, creates 100 Hz or 120 Hz modulation of
the light output from fluorescent lamps operated with high
frequency electronic ballasts.

I have run a series of measurements on various
electronically ballasted CFLs and found substantial amounts
of 120 Hz flicker; typically 1/3 to 1/4 as much as found in
linear lamps operated at 60 Hz on EM ballasts. I have also
located an obscure paper (Study on Fluorescent Lamp
Illumination and Flicker; Xiaoming, Ke, Ying & Wenziang;
Fifth International Conference on Power Electronics and
Drive Systems, 2003) that reports flicker index measurements
of 1.1% to 5.4% for 36-watt linear fluorescent lamps
operating on electronic ballasts. (This same lamp had a
flicker index of 8.8% when operated on an EM ballast.)

If you attended Light fair 2007 and received one of the
"Flicker Checker" tops provided by Sylvania you can run your
own experiments. Line frequency operated fluorescent lamps
will show strong strobe lines as expected. However, you
will be able to observe weak strobe lines when the spinning
disk is illuminated by CFLs or even line powered
incandescent lamps. The only light sources that I have
found that do not produce strobe lines are flashlights and
sunlight.

While I strongly suspect that the lower percentage flicker
from fluorescent lamps operated on high frequency electronic
ballasts will reduce the likelihood of people developing
headaches, the data shows that we can no longer rule out the
possibility that some people may develop headaches even when
using electronically ballasts linear and compact fluorescent
lamps.

Note that the same flicker issues will apply to LED lighting
systems. LED flicker may be worse than Fluorescent lamp
flicker because, unlike a fluorescent lamp ballast, there is
no technical reason to filter the DC power link at all. In
addition, LEDs that do not use phosphor have faster response
time than the phosphors used in fluorescent lamps. On the
other hand, many LED systems employ some sort of current
regulator, which may serve to reduce the percentage ripple
in the LED drive current relative to that on the internal DC
power supply.

I don't know of any studies that show the prevalence of
lamp flicker induced headaches as a function of flicker
index. If no such studies have been done they need to be
undertaken. In addition, based on a pervious discussion in
this group initiated by Terry McGowan, I believe this data
shows that Energy Star needs to add a flicker limit to the
Energy Star Requirements for both CFLs, and LED-based
fixtures.

Ira and I will be submitting a letter on this subject to
LD+A and a longer paper with data will probably be submitted
to the IEEE Transactions on Industrial Applications or the
Journal of the Illuminating Engineering Society. The data
will also be posted at www.cflfacts.com.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Victor Roberts]

It is generally known that fluorescent lamps operated on
line frequency EM ballasts produce a substantial amount of
flicker at twice the power line frequency: 100 Hz or 120 Hz
depending upon country. This flicker is known to cause
create headaches in some people.

[snip for brevity]

Ira and I will be submitting a letter on this subject to
LD+A and a longer paper with data will probably be submitted
to the IEEE Transactions on Industrial Applications or the
Journal of the Illuminating Engineering Society. The data
will also be posted at www.cflfacts.com.

Vic, from testing three-four types of my fluorescents driven by regular
ballasts, I can see the following:

PHILIPS TL-D/30W/55 strong flicker, with no phosphor persistence
PHILIPS TL-D/30W/54 strong flicker, with some phosphor persistence (yellow)
OSRAM DULUX 21W/2700K CFL no perceptible flicker
NARVA 21W/6000K CFL no perceptible flicker

It seems to me that the ones which produce the most flicker are the older
halophosphate linear fluorescents. I tried carefully to perceive flicker on the
DULUX/NARVA CFLs, but I was not able to.

I think the triphosphors on regular CFLs have a very long persistence which
prevents perceptible flicker and hence I was not able to detect anything
substancial. I also ran a couple of fast rotating devices (like fans) under the
DULUX/NARVA and could not see a strobo effect.

Perhaps the flicker is dependent also on the size of the lamp?

The flicker is most definitely dependent on the size of the
lamp and the phosphor used and other factors. However, I do
not believe your "perception" of flicker is sufficient.

You may not be sensitive to flicker. I am not sensitive to
flicker. I do not perceive any flicker from the CFL that I
use on my desk, yet can measure the flicker using a detector
and my oscilloscope or with the Sylvania "Flicker Checker."
Since we know that the lamp is flickering, even by a small
amount, we cannot tell people who claim to get headaches
from these lamps that "it is not possible because they use
electronic ballasts." I think we now have an obligation to
run controlled tests to determine what level of flicker can
trigger these headaches.

Note that incandescent lamps also have measurable flicker;
your 50 Hz lamps more than our 60 Hz lamps. Yet, as far as
I know, few people complain of headaches when using
incandescent lamps. These are fertile areas for study
here.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Victor Roberts]

Victor Roberts wrote:
[snip]

The flicker is most definitely dependent on the size of the
lamp and the phosphor used and other factors. However, I do
not believe your "perception" of flicker is sufficient.

You may not be sensitive to flicker.

I am VERY sensitive to flicker and I know how to recognize it immediately, thank
you. LEDs annoy the heck out of me for example and so does tv and old CRTs

I think what you meant to say was that I am not "psychologically sensitive" to
flicker. See below please.

I am not sensitive to
flicker. I do not perceive any flicker from the CFL that I
use on my desk, yet can measure the flicker using a detector
and my oscilloscope or with the Sylvania "Flicker Checker."

I think we are talking about two different things here:

1) Psychological "sensitivity" (causes headaches?)
2) Perceptual "sensitivity".

In my mind, psychological sensitivity would cause the headaches. Perceptual
sensitivity is just an observational curiosity and thus benign (at least for
me).

From GE's engineering catalog, the average frequency of "detectable" perceptual
flicker is around 24-30 Hz, which is roughly the rate the individual screenshots
propagate in a regular movie theater, creating the illusion of continuity.

It's safe to assume that anything lower than 24-30 Hz would indeed be
"perceptible" by a normal human being. In particular 50Hz and 60Hz are not,
unless some other major factor plays a role here, like phosphor non-persistence
or fast movement of eyes or parts.

As you mention for the incandescent lamps there still is flicker, but since the
wire continues to be hot during cycles, the perception of flicker is inhibited.

If there was a perceptible flicker on CFLs I would notice it easily. Note the
connection: No perceptible flicker on my USB desktop triphosphor cold cathode
lamp, which is identical to the cold cathode source that illuminates the back of
my laptop's screen.

Most people who use laptops would be affected adversely staring at those laptop
screens for hours, if they were "psychologically sensitive" to CFL flicker. They
would also be affected adversely just by watching regular tv or going to a
regular movie.

I agree that since the source is AC there's always flicker, but if this flicker
can be measured only by an oscilloscope, does it make sense to say that it's
"perceptible"?

Perhaps it is "psychologically perceptible", but I don't think it is "visually
perceptible". My own eyes work perfectly well

Since we know that the lamp is flickering, even by a small
amount, we cannot tell people who claim to get headaches
from these lamps that "it is not possible because they use
electronic ballasts."

Ok. But we can tell them that there is no PERCEPTIBLE flicker, so their
condition is unique insofar that it deviates from the norm. A "normal" observer
does not detect flicker in CFLs.

I think we now have an obligation to
run controlled tests to determine what level of flicker can
trigger these headaches.

Note that incandescent lamps also have measurable flicker;
your 50 Hz lamps more than our 60 Hz lamps. Yet, as far as
I know, few people complain of headaches when using
incandescent lamps. These are fertile areas for study
here.

In my opinion, for "psychologically sensitive" people, there probably exists a
certain threshold frequency, below which they would get headaches. This
threshold would tend to become more pronounced with longer and larger
fluorescents, but it sounds a bit nonsensical to me for someone to claim that
CFL's "flicker" while tv or cinema projection doesn't, for example.

I agree that it is an interesting area of research, however and most likely
connected to the subjective perception of light with interesting links to
psychology. It is known for example that strong perceptual flicker is a major
precursor of seizures in people with epilepsy, so some research has been done in
this area.

I apologize if I was not clear. I do not mean what you
call perceptible flicker.

Let me repeat again what the issue is.

Some people have a history of getting headaches when exposed
to fluorescent lighting. Some of these people (or perhaps
others) have complained that modern CFLs also give them
headaches. These comments are being made in the context of
energy regulations that propose to ban incandescent lamps in
favor of CFLs and other higher efficacy sources.

The "typical" response to these complaints often is: "the
fluorescent lamps that gave you the headaches were operated
at 60 Hz (or 50 Hz). The light output from these lamps did
vary periodically at frequencies that could have caused your
headaches. However, these new CFLs operate at frequencies
greater than 20 KHz so any periodic variation in light
output occurs at such a high frequency that they cannot
cause headaches."

The data we have obtained shows that the statement given in
the previous paragraph is not correct. CFLs that use high
frequency electronic ballasts can still have a significant
amount of flicker. The amount of flicker depends upon the
design of the ballast and, to a lesser extent, the lamp.

So the distinction between line frequency and high frequency
fluorescent lamps is not "flicker vs. no flicker", but
"flicker vs less flicker." Since I have not seen any data
indicating how much flicker is necessary to trigger
headaches in people who are sensitive to this effect, I can
no longer rule out the possibility that CFLs using
electronic ballasts (and by extension some LED systems) will
cause some people to have headaches.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Victor Roberts]

Victor Roberts wrote:
[snip]

I apologize if I was not clear. I do not mean what you
call perceptible flicker.
OK.

Let me repeat again what the issue is.

Some people have a history of getting headaches when exposed
to fluorescent lighting. Some of these people (or perhaps
others) have complained that modern CFLs also give them
headaches. These comments are being made in the context of
energy regulations that propose to ban incandescent lamps in
favor of CFLs and other higher efficacy sources.

The "typical" response to these complaints often is: "the
fluorescent lamps that gave you the headaches were operated
at 60 Hz (or 50 Hz). The light output from these lamps did
vary periodically at frequencies that could have caused your
headaches. However, these new CFLs operate at frequencies
greater than 20 KHz so any periodic variation in light
output occurs at such a high frequency that they cannot
cause headaches."

The data we have obtained shows that the statement given in
the previous paragraph is not correct. CFLs that use high
frequency electronic ballasts can still have a significant
amount of flicker.

I am lost. How can the "flicker" from a 20kHz source cause headaches, when tv or
regular cinema (which has a VERY perceptible flicker) doesn't?

Because the 20 kHz signal is amplitude modulated at 120 Hz.
Therefore the light now has a significant 120 Hz component.

Does it seem logical to you?

Yes, when the high frequency signal is modulated at a low
frequency such as 100 Hz or 120 Hz.

In my mind, the more away the frequency is from 25-30 Hz upwards, the lesser the
effect (if any).

I would agree. But we are talking about 120 Hz modulation
of the light.

And by your own admission, we are not talking about "perceptible" flicker. So
what the heck ARE we talking about if the flicker is non-perceptible?

We are talking about the same 120 Hz flicker that many
people believe is responsible for giving some people
headaches.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Victor Roberts]

Victor Roberts wrote:
[snip]

I am lost. How can the "flicker" from a 20kHz source cause
headaches, when tv or regular cinema (which has a VERY perceptible
flicker) doesn't?

Because the 20 kHz signal is amplitude modulated at 120 Hz.
Therefore the light now has a significant 120 Hz component.
[snip]

We are talking about the same 120 Hz flicker that many
people believe is responsible for giving some people
headaches.

I see. Thanks. My question remains, albeit somewhat modified:

How can the "flicker" from a 100-120 Hz (light) source cause headaches,
when tv or regular cinema (which has a VERY perceptible flicker) doesn't?

I don't know. Perhaps Terry has a better understanding of
this. It's possible that the same small segment of the
population that gets headaches from fluorescent lamps also
gets headaches when viewing movies, TV or computer monitors.

Additionally, a 120 Hz flicker is non-perceptible to the normal eye,
so it seems very strange to me, but I guess I'll believe that it happens...

My understanding is that just because you are not conscious
of the flicker it does not mean that your eye/brain system
is not detecting and processing it.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Andrew Gabriel]

It is generally known that fluorescent lamps operated on
line frequency EM ballasts produce a substantial amount of
flicker at twice the power line frequency: 100 Hz or 120 Hz
depending upon country. This flicker is known to cause
create headaches in some people.

My suspicion (unproven) is that this is not the primary or
most likely cause, i.e. flicker at 100 Hz or 120 Hz is not
primarily responsible for this.

Flicker at 50 Hz or 60 Hz is, and this results from tubes
which are partially rectifying due to different behaviour
of the two cathodes. This is particularly obvious during
the last few hours of tube life as one of the cathodes is
running out of emissive coating, but may also apply to poor
quality tubes throughout their lives.

 

[Andrew Gabriel]

How can the "flicker" from a 100-120 Hz (light) source cause headaches,
when tv or regular cinema (which has a VERY perceptible flicker) doesn't?

I would suggest TV/cinema is generally viewed in centre of gaze
which is much less perceptible to flicker. I believe the rate at
which a series of images looks to be a continuous movement is the
Optical Fusion Frequency, and it quite low for a human.

General lighting will normally apply to the full field of view,
which includes the black and white peripheral vision, which is much
more perceptible to flicker.

Additionally, a 120 Hz flicker is non-perceptible to the normal eye,
so it seems very strange to me, but I guess I'll believe that it happens...

Actually, the eye perceives 120Hz without any problem -- it can be
measured in the optic nerve. I suspect the problem is that our brains
are too big to be able to process data at this rate -- the max rate our
brains can perceive flicker varies by person but has a max value of
about 70 Hz. Conversely, it is believed a fly can perceive flicker at
up to 1000 Hz, having a much smaller brain.

Even though we can't perceive the flicker at 100 Hz or 120 Hz,
parts of the brain will be receiving this signal.

 

[Victor Roberts]

My suspicion (unproven) is that this is not the primary or
most likely cause, i.e. flicker at 100 Hz or 120 Hz is not
primarily responsible for this.

Flicker at 50 Hz or 60 Hz is, and this results from tubes
which are partially rectifying due to different behaviour
of the two cathodes. This is particularly obvious during
the last few hours of tube life as one of the cathodes is
running out of emissive coating, but may also apply to poor
quality tubes throughout their lives.

An interesting point. One of the F14T12 lamps that was
running on an EM ballast had distinctly unequal half cycle
intensities, leading to a significant 60 Hz component in the
frequency spectrum of the light output.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Ken]

Actually, the eye perceives 120Hz without any problem -- it can be
measured in the optic nerve. I suspect the problem is that our brains
are too big to be able to process data at this rate -- the max rate our
brains can perceive flicker varies by person but has a max value of
about 70 Hz. Conversely, it is believed a fly can perceive flicker at
up to 1000 Hz, having a much smaller brain.

I see the 85 Hz flicker from my CRT computer monitor
when it's sunlight in the room.
Unfortunately my monitor can't be set higher than 85 Hz.

 

[Victor Roberts]

Robert Miehle has done some measurements on HQI, fluorescent and
incandescent lamps:

<http://www.hereinspaziert.de/VG-Licht/Licht_VG2.htm> (in German)

He has used a photodiode BPW21R and a Fluke 192 Scopemeter to measure the
luminous flux. This photodiode has a filter which approximates the spectral
response of the human eye.

Trace B of the first diagram shows the luminous flux of a Philips MHN-TD 70W
lamp driven by an Osram POWERTRONIC® PTU 70 electronic ballast. According to
the description the flicker index is about 5 % at 130 Hz (= operating
frequency of the PTU square wave inverter). The third diagram shows the
luminous flux of the same lamp driven by a Tridonic OMBIS 70 electromagnetic
ballast. The flicker index is about 42 % at 100 Hz.

The fourth diagram shows the luminous flux of an incandescent light bulb.
The flicker index is 10 % at 100 Hz.

The fifth diagram shows an Osram L36W/830 fluorescent lamp driven by an
electronic ballast. The flicker index is about 3 % at 100 Hz. The last
diagram shows the samp lamp operating at an electromagnetic ballast. This
configuration has a flicker index of nearby 40 % at 100 Hz. Osram itself
states that the flicker index of their Quicktronic ballasts is about 5 %
whereas the flicker index of electromagnetic ballasts ist between 40 and
60 %.

The European Standard 61000-3-2 sets high restrictions on lighting devices
with a power consumption greater than 25 W with regard to THD. Therefore
most electronic ballasts here include an electronic PFC stage which implies
a stabilized DC voltage for the inverter. Hence the flicker of the
fluorescent lamp should be low.

Robert has not tested CFLs, but as you said it really depends on the
smoothing capacity after the rectifier.

Christian.

Thanks for the reference. I translated the page with
Google Translate and it will be very helpful. One comment
ZI have is that I do not believe the authors are reporting
the Flicker Index, at least as defined by the IESNA. They
are seem to be reporting a value equal to:

(peak-to-peak ripple)/(2*mean)

which would be:

peak ripple /mean

for symmetrical ripple.

The IESNA definition of ripple factor is area based instead
of peak value based.

The Xiaomong paper I cited also showed low flicker values
for a ballast using active power factor correction, but one
of the CFLs I tested also used active PFC but had a
significant amount of ripple. So, I don't believe that
active pfc will guarantee low ripple.

--
Vic Roberts
http://www.RobertsResearchInc.com
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[Don Klipstein]

I see the 85 Hz flicker from my CRT computer monitor
when it's sunlight in the room.
Unfortunately my monitor can't be set higher than 85 Hz.

In my experience when a monitor has vertical scan rate that fast, it
interlaces, even if it claims to be a non-interlaced monitor. If there is
any difference between the odd number field and the even number field, you
could get flicker at the frame rate which is half the vertical scan rate.

I usually see a monitor flicker at 56 Hz, sometimes see a monitor
flicker at 60 Hz, though I have yet to see one flicker at 72 Hz.

- Don Klipstein ([email protected])

 

[Don Klipstein]

I just don't understand what the fuss is all about, when for example, huge
basketball courts and stadiums are illuminated by metal halides which have a
VERY perceptible flicker, versus CFLs for which people complain.

I have seen a trick done with at least some stadiums: Use 3-phase
power, and have 1/3 of the lamps in each lamp array operated from a
different phase.

I believe this is necessary for most video cameras to work in stadiums.

Also, larger metal halide lamps such as the 1000 and 1500 watt ones used
for stadiums have a higher ratio of mercury vapor mass to power than
smaller ones. The high thermal mass of the mercury vapor reduces flicker,
though the flicker is still worse than that of most incandescent lamps.

- Don Klipstein ([email protected])

 

[TKM]

Some years ago in the UK some work was undertaken on this very topic
of which I have some recollection and which may be relevant if you can
find the source.

The luminairs were switch start (before the days of HF ballsts) in an
office environment and flicker was suspected as being a cause of some
discomfort in some people. Electromagnetism (of course) also raised
its head as a possible cause but it was eventually shown that sub
audio from the fittings was the main culprit.

Maybe someone out there can offer you the reference (my memory is a
fading bloom) to see if it is relevant - I would not want you to spend
ages seeking such only to find that it was 'quack' science!!

regards

Yes, I recall the reference and I should have posted it earlier since it has
been my basic reference on the subject.
It is: G.W. Brundrett, "Human sensitivity to flicker". Light. Res. Technol.
6 (1974), pp. 127–143.

I couldn't find the paper on line; but I've asked LR&T if it is still
available.

Terry McGowan

 

[Victor Roberts]

Yes, I recall the reference and I should have posted it earlier since it has
been my basic reference on the subject.
It is: G.W. Brundrett, "Human sensitivity to flicker". Light. Res. Technol.
6 (1974), pp. 127–143.

I couldn't find the paper on line; but I've asked LR&T if it is still
available.

Terry McGowan

Thanks Terry. It would be very useful to have a copy.

--
Vic Roberts
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[TKM]

Not sure if it makes sense to post with all the unrelated messages on
the list, but here goes:

Thanks for good descriptions of flicker, this thread was very
educational for me.

fluourescent lights could have a stroboscopic effect on power tools
and cause injury in a home shop. (Making a bandsaw look like its
turned off until you touch the blade, etc.)

None of the flicker you all have mentioned seems anywhere near large
enough to cause a strobe effect.

If by "strobe effect" you mean the illusion that moving machinery is stopped
even though it is moving and potentially dangerous, then, no, the visual
effects we've been discussing are not likely to do that. I've always been
suspicious that it was a made-up problem anyway. Even when I tried to
create the effect in machine shops or on the test bench with motors and
flash tubes, it was tough. Moving machinery tends to drift in speed and
getting everything to synchronize is tricky. Those who have tried to set
the turntable speed exactly for long-playing records before electronic
synchronization came along may want to comment too.

My favorite test was at one of the power generating plants at Niagara Falls.
During a tour we explored the turbine building and were able to view (and
touch!) the shafts from the water turbines to the generators. There was
single-tube fluorescent lighting in the area (electromagnetic ballasts); but
even though the shaft speed was carefully controlled and obviously
synchronized to produce 60 Hz. there was little strobe effect and the
shafts certainly did not appear to be stopped.

Sports lighting people sometimes complain that strobe causes problems with
viewing moving baseballs and footballs (the balls apparently seem to
visually jump from position to position confusing the players); but I've
never been able to confirm that problem either.

Terry McGowan

 

[JohnR66]

If by "strobe effect" you mean the illusion that moving machinery is
stopped even though it is moving and potentially dangerous, then, no, the
visual effects we've been discussing are not likely to do that. I've
always been suspicious that it was a made-up problem anyway. Even when I
tried to create the effect in machine shops or on the test bench with
motors and flash tubes, it was tough. Moving machinery tends to drift in
speed and getting everything to synchronize is tricky. Those who have
tried to set the turntable speed exactly for long-playing records before
electronic synchronization came along may want to comment too.

My favorite test was at one of the power generating plants at Niagara
Falls. During a tour we explored the turbine building and were able to
view (and touch!) the shafts from the water turbines to the generators.
There was single-tube fluorescent lighting in the area (electromagnetic
ballasts); but even though the shaft speed was carefully controlled and
obviously synchronized to produce 60 Hz. there was little strobe effect
and the shafts certainly did not appear to be stopped.

Sports lighting people sometimes complain that strobe causes problems with
viewing moving baseballs and footballs (the balls apparently seem to
visually jump from position to position confusing the players); but I've
never been able to confirm that problem either.

Terry McGowan

I can see a single phase supply to HID lighting on a ball field being a
problem with strobing. I'd guess 3 phase delivered to each lighting tower
and each phase distributed among the lights on the tower would elliminate
the problem.

 

[TKM]

I can see a single phase supply to HID lighting on a ball field being a
problem with strobing. I'd guess 3 phase delivered to each lighting tower
and each phase distributed among the lights on the tower would elliminate
the problem.

Yes, a 3-phase supply seems to eliminate the visual strobe effect from what
I've seen; but that solution depends upon the light from at least three
lighting fixtures simultaneously illuminating the moving object. The
tendency in outdoor lighting is to use fewer high-wattage fixtures which
tends to minimize lighting overlap and cost ( and maximize glare).
Fortunately, with the outdoor lighting design software in use these days,
it's easier to sort that all out and determine beforehand how each fixture
should be aimed.

Terry McGowan

 

[TKM]

While I don't believe it makes any sense, I'll paste a snip from the
safety rules at a US university machine shop:

Lighting
DC lamps must always be turned on when using any rotating machines.
The main fluorescent lights in the machine shop run off the 110 V, 60
Hz electrical supply and effectively strobe at 60 or 120 Hz. Machines
that rotate at harmonics of 60 Hz will appear to be stationary. For
this reason, all rotating machines in the shop have a DC lamp beside
them. Use the lamps! Otherwise you might try to reach for a spindle
that looks stationary but is rotating.

Wonderful! Do you know how old that notice is? The logic is classic; but
it would be fascinating to talk with the people in the shop to see if they
had ever tested the assumption. It would also be interesting to know how
the DC lamps were powered so as to see if they did indeed eliminate the
modulation from the DC.

Terry McGowan