
The scientific reason you don’t like LED bulbs – and the simple way to fix them - ValentineC
https://theconversation.com/the-scientific-reason-you-dont-like-led-bulbs-and-the-simple-way-to-fix-them-81639
======
abainbridge
What gets me are side-lights on cars that flicker. Cars have DC electric
systems in the first place. Where did the Audi engineers find 100 Hz to run
the LEDs from?

I guess there's a switch mode power supply to convert down from 12 V to
something lower that the LEDs need. But AFAIK, switch mode power supplies
don't switch at 100 Hz.

I'm pretty sure you could show by experiment that flickering car side-lights
are distracting. For example, in a situation where you are pulling out of a T
junction in the dark, you're less likely to see a motorbike when it is in the
same part of your visual field as a car with flickering lights. Particularly
when you are moving your head from left to right, as you do when at a T
junction.

I'm not sure how to do the experiment though, since using TV screens, monitors
or projectors wouldn't work.

~~~
KaiserPro
I suspect its not the PSU, its the PWM for the dimming.

compared to actually lowering the voltage/current of a LED/light/other its far
simpler and cheaper just to turn it off and on again at varying duty cycles/
frequency.

~~~
mollusk
Correct me if I'm wrong, but isn't it just the de facto way of dimming LEDs?
Since as opposed to incandescent bulbs, they require certain voltage/current
to be lit, if you pass them less, they simply won't emit light.

~~~
colanderman
They require a certain voltage (to a first approximation). Their light output
is (again, to a first approximation) directly proportional to the applied
current.

PWM control is just a cheap way of reducing the current.

------
cjsuk
I've had this problem and decided to test the problem away. Used a Vishay
visible spectrum phototransistor and my scope. Think it was a BPV11
transistor.

Philips bulbs are 100% clean. Poundland ones are not. Cheap no brand ones from
Amazon are not. The latter two have a 100Hz output.

I suspect the hatred for LED bulbs stems from the cheap ones which use the
lowest cost solution to get mains voltage into a constant current which is
usually a capacitive dropper and rectifier with an inadequate smoothing cap.

Really as always with these things, buy the best you can.

Also the cheaper ones seem to have a blue/white tone whereas the expensive
ones have a yellow/white tone and are warmer. This helps the eyes.

~~~
Zak
Another issue is that many LEDs have peaky spectra. This makes cool white
harsh and warm white dingy. This isn't limited to cheap products, as producing
a fuller spectrum with LEDs is less efficient.

I'll take the efficiency hit for better light; the most common measure used,
printed on the packaging of some bulbs is CRI (color rendering index). It's
based on blackbody radiation, so incandescent bulbs and sunlight both have the
maximum score of 100. The average unspecified LED is in the 60s and sodium
vapor lamps are _negative_. 90 is good for an LED, and 97 is the highest I've
heard of someone testing in an LED[0].

CRI isn't the whole story on color quality, and it's possible to have high CRI
with off tints or even a peaky spectrum outside of the specific colors the CRI
standard tests, though the latter doesn't happen in practice. Several newer
standards for measuring color quality exist, but are unlikely to be listed on
a light bulb label.

[0]
[http://budgetlightforum.com/comment/1096106#comment-1096106](http://budgetlightforum.com/comment/1096106#comment-1096106)

~~~
oasisbob
Agreed! It took several tries to get LEDs which worked well for vanity (i.e.
Mirror) lighting. I thought it was a simple matter of color temperature - so
wrong!

High CRI strip LED arrays are surprisingly hard to find. The end result was
worth it though - skin looks natural, and the nearest commercial version is
upwards of $800 - and I'm not entirely sure they got the CRI right.

~~~
w458cmau
Which solution did you end up with?

~~~
oasisbob
I ended up with a strip from colordiode, they're available on ebay. Was
described as CRI>95 3000~3200K SMD2835, 90/m. Came with a pretty decent
datasheet, seemed well-characterized. Cost was ~ $10/meter. They were
responsive enough to include a few samples of other color temperatures with
the order when I asked nicely.

The housing used was extruded aluminum u-channel by Torchstar (U05,
semicircular), very nice clean finish. Available on Amazon.

Like I mentioned, this was for vanity lighting - there's a full length mirror
in the closet that's wedged on the wall between a closet door and a window.
Not much room for anything else. Hung two vertical strips, ~ 4ft long, on each
side of the mirror.

Light ended up soft, diffuse, and flattering - but still directional enough
for good modeling. Significant other couldn't have been happier.

------
zkms
I hate it when LED light output isn't continuous or visibly flickery,
especially when it's from LED lights that are on (or are visible from) moving
objects -- such as LED taillights on automobiles or in-road lane lights. All
the eye movement (or object movement) makes the flicker even more flagrant :(

I remember extremely flickery lane lights on the leftmost lane markers on
California's infamous SR 110, on the northbound direction (towards Pasadena)
in the tunnels (the ones right before the left-exit to I-5 north).

Good fluorescent bulbs will have electronic ballasts (the driving circuit)
that supply current to the bulb with a higher frequency (in the low kilohertz)
than the time response of the bulb's phosphor. Thus, any sort of flicker gets
low-pass filtered and isn't significantly noticeable in the output light.

Even with a subpar magnetic ballast that drives the bulb with line frequency,
the phosphor never gets close to fully extinguishing -- so there is flicker,
but the instantaneous light output never gets less than, say, half the maximum
instantaneous light output. Look on page 3 of
[http://www.usailighting.com/stuff/contentmgr/files/1/e18f88d...](http://www.usailighting.com/stuff/contentmgr/files/1/e18f88d078a54622682528e496596192/misc/flickerfactsheet_doe.pdf)
for some instantaneous light vs time graphs for fluorescent bulbs.

LEDs have a much higher frequency response (in the tens of megahertz, easily)
-- they respond quicker and more faithfully replicate their electrical drive
signal as light output. You can see on page 4 of that report how violently
jagged the LED's light/time plots can get.

If the manufacturer didn't want to include adequate filter capacitors in the
LED's driver because of cost/reliability concerns, well, I hope your eyes
enjoy that signal because the LED, unlike the fluorescent bulb, isn't going to
smooth it out.

~~~
perilunar
Those LED plots are pretty crazy. Surprising how much incandescent lights vary
though (10-20% according to the plots) — would have it would have been much
less than that.

------
gargravarr
I find this a problem with my LED-backlit LG monitor. It's ridiculously (by
which I mean, blindingly) bright at full brightness, but anything below and
the imperceptible flicker gives me migraines. So I have the choice of
impossible brightness with no flicker, or acceptable brightness with
headaches.

I don't get why LED bulbs need to flicker though - the bulbs don't dim, and if
they're providing steady light, they should be operating permanently. If it's
a heat production problem, the bulbs need heatsinks, not PWM.

I've found a vast array of modern tech to be completely unusable for me
because of this. I can stare at the CCFL-backlit screens on my workstation all
day, but a few minutes of my home monitor is enough to send me straight to bed
in darkness.

~~~
arantius
> I don't get why LED bulbs need to flicker though

It's _much_ cheaper/easier to blink an LED on/off for 75% of the time than to
drive a constant but lower current to produce 75% of the brightness. Most
products are cost optimized.

------
Neil44
From experience there's a massive difference in the quality of light from a
cheap LED bulb to an expensive one which I don't think is something that the
bulk of consumers are aware of yet.

~~~
aembleton
There's also a massive difference in how long they last for. The cheap ones
use cheap components that fail after a year or so. The LEDs might last a
decade but the cheap drivers won't.

For those in the UK, I can recommend Screwfix LEDs. They seem to be lasting
for me, don't flicker and are relatively cheap at £2/bulb
[http://www.screwfix.com/p/lap-gls-led-light-bulbs-white-
bc-9...](http://www.screwfix.com/p/lap-gls-led-light-bulbs-white-
bc-9w-5-pack/2330j)

------
gustavam
You can see the flicker of your light sources for yourself if you have a slow
speed camera. iPhone 6s/SE/7 can record at 240FPS. Point that at your LEDs,
fluorescents and incandescents. Try your computer screen as well. I did this
half a year ago and can confirm. Cheap LEDs are really bad, some more
expensive ones don't flicker at all. Cheap computer screens flicker as well.
Whenever I find a light source that I don't like somehow but can't quite say
why, I record it slowmo and usually it turns out it flickers.

------
tbrownaw
Most of my led lighting is dimmable, and takes noticeable time to go dark
after I flip the switch to off. The ones that actually have dimmer switches
installed also take noticeable time to come on when set as dim as possible. I
seriously doubt that those bulbs have flicker problems.

~~~
roel_v
It's quite likely that that's intentional 'soft on/off' behavior that's been
engineered into the dimmer. My lights at home do this too, but I can turn it
on/off. Some LED bulbs don't deal with it very well - depending on whether the
driver in the bulb themselves expect leading or trailing edge dim signals (in
the case where you send mains voltage to the bulb and the bulb has in internal
driver; this is different when you have a full DC circuit).

------
jonsen
Say you have an LED which can sustain 1 Watt of continuous power. If you feed
it 10 Watt in fast pulses with a pulse/pause ratio of 1:9 it would still be 1
Watt on average, but the light intensity impression to the human eye would be
higher.

------
Osmium
Weird, I've never had issues with LED bulbs, but I routinely have headaches
from fluorescent. Maybe I've just lucked out with my specific bulbs being
higher quality (Ikea, Philips Hue). I imagine color spectrum is a large part
too.

~~~
oppositelock
Me too - constant headaches from fluorescent lights, none from LED. I buy the
less efficient full-spectrum LED lights which have a phosphor. The phosphor
probably filters the underlying LED flicker.

~~~
Osmium
Yeah, I think my Ikea ones are phosphor, the Philips Hue are RGB though and
still fine.

~~~
seanp2k2
Anyone know what the LiFX bulbs use? We have a dozen of them and the
adjustable color temp is great. I also have a box of smaller LED bulbs from
Home Depot. Neither hurt my eyes and I don't (didn't, will see now that I'm
paying attention) notice a difference, but I'm sure there is one.

I also wonder about e.g. The Anker desk lamps, where the bulb is built in. I
have one behind my monitor with the head turned round (it's designed to do
this) to throw light up the wall behind my monitor as bias lighting, and
another (their clamp lamp) on my electronics desk. They're great lamps with
annoying touch power buttons, but both are adjustable color temp and have
built-in LEDs which never require changing.

~~~
Osmium
LiFX let you set the color right? So by definition they're going to be RGB
(have three colored LEDs inside). Generally, LEDs that are single color are
more likely to be phosphor (blue LED inside with a phosphor that converts to
yellow).

------
amelius
Reminds me of the effect of using an electric toothbrush, and simultaneously
looking at a LED indicator of e.g. a washing machine. It is explained here:
[1].

[1] [https://electronics.stackexchange.com/questions/32675/why-
do...](https://electronics.stackexchange.com/questions/32675/why-do-7-segment-
led-displays-break-apart-when-i-brush-my-teeth)

------
Rjevski
I recently got myself some LIFX smart bulbs and I don't notice any flicker or
discomfort. So maybe the morale of the story is to stop buying shit bulbs?

------
kabes
But then wouldn't our 60Hz screens have a much bigger impact on office workers
than the lights above them?

~~~
garaetjjte
On CRT screens yes, but backlight in LCD screens is LED/fluorescent driven by
much higher frequencies. Though some LCD screens still flicker, but it is
visible only on special patterns: [http://www.lagom.nl/lcd-
test/inversion.php](http://www.lagom.nl/lcd-test/inversion.php)

~~~
TMSZ
Not necessary much higher. I've measured screen flickering in Lenovo T500
(probably one of the oldest laptops with LED backlight) with small solar cell
and oscilloscope and it's 220Hz, with lowest brightness setting only 100Hz
(although this brighness level is not too useful):
[http://commonemitter.blogspot.com/2017/06/lenovo-t500-measur...](http://commonemitter.blogspot.com/2017/06/lenovo-t500-measuring-
screen-flickering.html)

