This is a stroboscope disc used to verify
the speed of a record player’s turntable.
You can easily find these online and print
them out.
Under fluorescent lighting, these alternating
white-black bars will appear stationary even
though the turntable is rotating.
This happens because the A/C electricity powering
the light is a 60 hz sine wave, and each time
it crosses the zero line, the light briefly
goes dark.
Essentially, fluorescent lights actually flash
120 times per second, and the spacing of these
bars is calibrated so that if the turntable
is going the right speed, they will move the
same distance as their width with each pulse
of light, which makes a blurred pattern appear
that’s completely stationary.
Slight variations in speed will cause the
pattern to appear to move.
You can see this as I switch the turntable
between 33 and 45 rpm.
You may have noticed a similar effect while
driving at night under common street lighting,
particularly the orange-gold glow of high
pressure sodium lamps.
These lights also pulse 120 times per second,
in the US at least, which can make slow-moving
patterns appear on the wheels of vehicles
driving past you.
Sometimes the patterns move backwards which
is particularly trippy.
This stroboscopic effect is the primary reason
that some people are sensitive to fluorescent
lighting.
Though it’s not directly visible, it can
give some people headaches and cause eyestrain.
But it’s important to note the the fluorescent-ness
of the light source is not what’s causing
it.
What I mean by this is that it’s very very
wrong to assume that all fluorescent lights
produce a strobing effect like this.
In fact, nearly all CFLs used in your home
don’t.
Here’s the same disc on the same turntable
with a garden variety CFL providing illumination.
This time, the disc’s lines just blur together.
CFLs have worked like this for a looong time.
In fact, here’s an old IKEA fluorescent
lamp.
It’s so old it starts like this.
(forced coughing)
And yet, the lines still blur together.
You might notice a very slight pattern in
there that looks stationary, but even an incandescent
light will produce such a faint pattern.
In reality, these CFLs are just as flicker-free
as the old bulbs of yore.
But in an odd twist, many newer LED bulbs
are re-introducing this stroboscopic effect.
Some are far worse than others, and first
let me say that I’m glad the CFL is being
replaced.
I am in no way trying to say that LED bulbs
are bad, and CFLs are somehow better.
Of course, a huge reason to be pro LED is
the lack of mercury in the bulbs.
And the list goes on--the slow warmup and
poor operation in cold weather of CFLs was
annoying, and LEDs don’t suffer from these
problems.
Poor color rendering indexes were common with
cheap CFLs which caused their perceived quality
of light to be not-so-great, whereas LEDs
almost always have better color rendering
characteristics.
Dimmability of CFLs was generally questionable
at best, and new LEDs go so far as to mimic
the warming effect that incandescent bulbs
naturally produce as their filaments burn
less intensely.
There’s virtually no reason to hold onto
the incandescent lamp anymore.
Even clear LED bulbs which look like they
have filaments are cheap and widely available.
So to explain why CFLs don’t flicker and
LEDs sometimes do, it’s important to look
at the electronics that drive each of these
technologies.
Fluorescent lights, along with all other discharge
lamps such as sodium vapor lamps or metal
halide bulbs, have a pesky electrical characteristic
known as negative resistance.
Provide a set voltage to the lamp, and it
will consume more and more current until it,
well basically explodes--or if it can manage
it, exhausts its electrical supply and trips
a breaker.
A ballast is therefore required to both strike
the arc and start the lamp, and most importantly
to limit the current it can receive and keep
things nice and safe.
In older fluorescent fixtures, this ballast
was nothing more than a specialized inductive
transformer, so-called magnetic ballasts.
These are what is responsible for the humming
or buzzing sound in older fixtures.
A magnetic ballast sends the same 60 hz electricity
to the tube, but with a limit in place.
This means the light will pulse on and off
120 times per second, which generally isn’t
directly perceptible, but can cause eye strain
in sensitive individuals.
Now, magnetic ballasts have two huge drawbacks.
One, they’re generally bulky, and two, the
fact that they send straight AC current to
the tube means the tube doesn’t run as bright
as it could because it spends a not-insignificant
period of time producing no light at all.
The pauses in light production reduce its
overall light output considerably.
When the Compact Fluorescent Light came along,
the compact nature of these compact bulbs
meant less actual glass tube was available
in such a compact space.
To compact a 16 watt 2 foot linear tube into
a space as compact as an ordinary light bulb
required some creative compacting action in
the form of glass bending acrobatics.
Compact.
First was the curly-q nature of the tube itself.
Forming the glass in a repeating spiral pattern
increases its surface area tremendously, while
still confining it into a small volume.
Then there was the problem of the ballast.
Remember, magnetic ballasts are bulky and
heavy.
A better solution was needed both to overcome
size constraints and to increase the light
output of such a small lamp.
Enter the electronic ballast.
These guys work entirely differently from
magnetic ballasts and were, uh what’s the
word, oh, compact and lightweight.
Electronic ballasts work similarly to the
switched-mode power supplies you find in virtually
everything today.
Their first goal is actually to convert the
incoming 60 hz AC power to DC, where it’s
filtered with a capacitor.
The ballast then converts this DC into very
high frequency AC power, around 20 thousand
hertz.
It’s this high frequency power that’s
sent to the tube.
The phosphors that line the inside of the
glass don’t react instantly to UV emissions
from the mercury vapor.
In fact, there’s a delay between when they
stop receiving energy from the excited mercury
molecules and when the stop emitting visible
light.
You can actually see this--the green phosphor
is the usually the slowest, and you might
have caught a slight green flash of light
when turning a off a light fixture with a
CFL if you’ve ever moved your eyes right
at the same time.
You see this because the red and blue phosphors
stop producing light in a tiny fraction of
a second, but the green phosphor hangs around
a little longer.
Anyway, the high frequency AC entering the
tube of a CFL is literally too fast for any
of the phosphors, and the delayed action bridges
the gap between pulses.
The result is that the light provides nearly
constant illumination, and the stroboscopic
effect is essentially eliminated.
Which can be proven by using one of these
do-dads.
Most newer linear fluorescent fixtures also
use an electronic ballast.
Even the old fashioned T12 tube will see a
significant increase in light output and efficiency
if high frequency A/C switching is applied.
For this reason, ceiling light fixtures using
linear tubes are nearly always equipped with
an electronic ballast these days.
Meanwhile, LED bulbs require a different kind
of circuitry to make them work.
LEDs only work with direct current, so for
a bulb on an AC supply, this AC needs to first
be rectified into DC using a bridge rectifier.
It’s not as simple as sending DC power through
the chips, though.
Without the proper voltage, the LEDs with
either be instantly destroyed or they won’t
work at all.
See LEDs have a very narrow range of operating
voltage, bumping it up by as little as half
a volt will dramatically increase current
consumed.
Drop it much below and it won’t light up
at all.
Because of this, they also need a ballast
of sorts.
Usually these are referred to as drivers.
The most important thing the driver has to
do is limit the current that passes through
the chips.
Without a way to limit the current, any voltage
above an LED chip’s forward voltage will
cause an exponential increase in current flow,
which will make the diode run extremely hot
and severely shorten its life.
In many conventional LED bulbs meant to replace
a 60 watt incandescent, there will be 9 or
10 chips, each rated around a watt.
These are usually arranged in a circle, and
are attached to a heat sink.
The heat sink absorbs the heat they produce,
and spreads it out over a wide area.
This bulb contains nine chips.
Each of these chips actually contains three
diodes in one package, so there’s a total
of 27 diodes arranged in series.
Most of the blue diodes used in white LED
chips--the yellow circle is a phosphor which
converts some of the blue light into red and
green, thus producing apparently white light--have
a voltage drop of just over 3 volts.
The driver therefore needs to produce at least
81 volts, and indeed it produces about 85.
The driver must also limit the current going
through this chain of diodes to ensure they
don’t overheat and waste energy.
It also uses a large capacitor hidden in the
base to store and release some energy between
the pulses of AC power coming from the socket
through bridge rectifier.
This helps to eliminate the stroboscopic flicker.
This capacitor is rather large and it’s
one of the biggest component of the driver.
But there’s also a way to cheat a little
bit.
LEDs can be driven off a direct voltage supply
if the voltage is equal to the voltage drop
across the LED chip.
Many so-called “filament” LED lamps are
designed with a bunch of blue diodes in series
along a glass rod covered in the yellow phosphor,
and the voltage drop across them adds up to
just about the same as the AC line voltage
powering the lamp.
If you dim one of these, you can see the individual
diodes along the filament’s structure.
These tiny diodes will also have a voltage
drop of about 3 volts, and since 120 volts
is what’s coming into the socket here in
the US, that could be divided across 40 individual
diodes.
Each of these rods has 20 diodes or so in
a line, and two rods are wired in series,
with another series-pair being in parallel.
In European countries running on 230 volts,
all four of these rods will be wired in series.
This cheat is what allows the driver to be
so small that it can be crammed into just
the space inside the socket.
This creates a beautiful bulb that you might
not even know it’s an LED unless someone
told you.
But there’s one huge drawback.
There’s so little space for the driver that
it doesn’t really do all that much.
In reality, nearly all it does is use a bridge
rectifier to convert the AC into pulsed DC.
That’s just taking this waveform and flipping
the bottom half back up.
This means these bulbs will often exhibit
stroboscopic flicker just as bad or worse
as a fluorescent bulb running from a magnetic
ballast.
In fact, that footage from earlier?
It was from this bulb, just with the color
temperature messed up a bit.
And now, a note from the editor’s desk.
Oh, hello, I’m the editor, and this is my
desk.
I’d just like to clarify that I’m sure
the driver is doing more than just rectifying
the AC into pulsed DC.
It’s actually a complicated little thing
with a driver chip, an inductor of sorts,
and other goodies.
What’s more likely the cause of the flicker
is simply that the driver’s tiny little
filter capacitor, a requirement with the driver
concealed in the socket, can’t store enough
charge to provide completely steady DC voltage
throughout the system as the incoming AC voltage
crosses the zero line.
The system voltage thus dips slightly between
each incoming pulse.
This is also probably the cause of the slight
flicker produced by the CFL, but the immensely
larger filter capacitor is able to provide
much more stable DC voltage to the rest of
the ballast.
In regards to the number of diodes along the
glass, I’m sure that’s geared towards
line voltage as it is common for European
bulbs to have all the rods wired in series,
but the driver is probably still providing
a different voltage for them.
I’m thinking it just makes the design of
the driver a whole lot simpler and cheaper
if it’s got to produce roughly the same
voltage as it receives.
If we have a qualified electrical engineer
in the comments, please do tell us if I’ve
got this all wrong.
I’m not even going to get into how these
bulbs work with dimmers because there’s
enough in there for a whole other video.
So then, here’s my point.
If you are an individual with photosensitive
epilepsy who has legitimately been affected
by fluorescent lighting in the past, this
type of LED bulb probably isn’t for you.
But if you’ve casually avoided compact fluorescent
lights believing them to cause eye strain
and you’ve been around these lights and
haven’t noticed a problem, perhaps it wasn’t
the, as I said, fluorescent-ness of the light
that caused your headaches.
As I’ve demonstrated, most CFLs produce
light just as well--meaning consistently and
without flicker--as an incandescent bulb.
But some newer LED lamps actually produce
really strong strobing light.
If these don’t affect you, that’s great!
But it also means that perhaps you shouldn’t
have been so averse to using the CFL.
One easy way to tell if a bulb has high flicker
is by bringing a smartphone camera right up
to the bulb.
With bright light the camera has to increase
its shutter speed a lot, which when combined
with the way it captures the light via a rolling
shutter, will make alternating bright dark
bands appear all over the image.
If bands are barely visible, then the flicker
is very minor.
Me again.
I discovered while shooting the B-roll for
this video that the old IKEA bulb exhibits
less flicker than an incandescent.
You can even see that going back to the stroboscope
disc footage.
These pictures shot with my phone confirm
it.
While we’re looking at pictures, light bulb
manufacturers have figured out how to produce
flexible filaments, and this one on display
in a retailer is shockingly bad!
However, one cool thing about the flexible
“filament” is that you can see the printed
circuit in the dark portion provided by the
absurd flicker of the bulb, and you can see
here that the diodes are wired as two series
chains, with each trace skipping every other
diode.
This means there are two parallel circuits
in each piece of filament spaghetti.
Now, I’ve long maintained a personal theory
that the folks most opposed to the compact
fluorescent were really more averse to the
blueish light of daylight color temperature
bulbs.
In fact, I hate those things.
I have a whole drawer full of them because
the previous owner of my place loved them,
and I just can’t stand the coldness of their
light.
I won’t go so far as to say they give me
a headache, but I dread being around them.
Because a well-made warm-white balanced CFL
is often indistinguishable from an incandescent,
particularly if the bulb is hidden behind
a shade, these people might have never noticed
that they were under fluorescent lighting
unless it was a cool white or daylight color
temperature, where it couldn’t possibly
be an incandescent.
But that’s just conjecture.
In reality, the CFL is on its way out, and
I’m happy to hear it.
So many great designs of LED bulbs are on
the market today, not even mentioning smart
bulbs or color-changing bulbs that are only
possible with LEDs inside.
But the CFL was a great innovation that helped
us start saving energy at home years before
LEDs came down in cost.
And if people just took the effort to recycle
them, the mercury wouldn’t have been much
of a concern.
But I’ll admit, a 100% recycling rate is
a pipedream.
Best avoid the problem all together.
Thanks for watching.
I hope you learned something interesting today!
I’m closing this video out with a thank
you and announcements.
To my subscribers, wow, I’m so thrilled
this channel has passed 35 thousand!
It still doesn’t seem real.
Having a successful YouTube channel has always
been a dream of mine, and it’s slowly becoming
reality.
But as you know, making videos
is really hard.
I’m doing my best to keep videos like this
headed your way, but I work full time and
it’s hard to do two things at once.
Which is why starting at the end of November,
I’m gonna stop doing two things at once.
I’m gonna concentrate on videos.
Hopefully I’ll be making weekly videos by
the start of next year, as I’ll have 4 days
a week to do this, and not just 2 if I’m
lucky.
There’s a lot of stuff up in this noggin
and eventually it will make its way out and
to your eyeballs and ears.
If all goes to plan, my next video will be
on Philo Farnsworth and the invention of electronic
television.
I’m overwhelmingly flattered that some people
have asked if I have a patreon page.
Well, I wanted wait and see if these types
of videos could earn me a following.
Apparently they have and now, I do have a
patreon.
In fact, it’s right over there.
I’m really new to this whole thing and don’t
really know what I’m doing, but if you’d
like to become a patron you will immediately
be rewarded with thanks and good vibes.
My biggest struggle right now is finding time
to do more management stuff, like make playlists
and set up a Patreon.
But if it works, I’ll be spending all of
my time making videos for you.
Thanks for watching.
