8 ms·

The scientific reason you don’t like LED bulbs – and the simple way to fix them

80 points by ValentineC 9y ago

Osmium 9y ago
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 9y ago
  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.
  - deleted 9y ago
    [deleted]
  - Osmium 9y ago
    Yeah, I think my Ikea ones are phosphor, the Philips Hue are RGB though and still fine.
    - seanp2k2 9y ago
      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 9y ago
        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).
    - inferiorhuman 9y ago
      I went to LEDs in my apartment about two years ago. 3 Hue bulbs + hub, some 48" T8 LEDs, and some E26 Ikea bulbs. The Ikea bulbs are great, power on instantly and slowly fade off. The T8s take about 3/4 second to turn on, and are nice and bright (and a far cry from the power consumption of the T12 florescent bulbs they replaced). The Hue bulbs... well, one's developed a noisy transformer. Replacements are, what, $40? Meh. I like the Zigbee integration, but not $40 in two years worth of like. And the CRI of the Hue is just as bad (actually worse) than the other bulbs. Lesson learned, those Ikea bulbs are great.
      - Osmium 9y ago
        Not trying to sell Hue here, but their bulbs have gone through several iterations by now. They were one of the first big names to push consumer LED bulbs, I wouldn't be surprised if their earlier versions had flaws just by being new. But maybe not, I don't know. (Also their color bulbs are $40, but they have much cheaper white ones, and also an in-between model they call ambiance which are white but allow you to adjust color temperature)
    - pjc50 9y ago
      Yes, you can tell the Ikea ones aren't flickery because they have huge phosphor persistence - several seconds after being turned off.
- ars 9y ago
  I've had the opposite, no problem with florescent, but many LED's drive me crazy - I keep seeing a "speckle pattern" like what a laser makes. If I don't move it's ok, but as soon as I look around I see a pattern of black and white areas from LED light.
Neil44 9y ago
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 9y ago
  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-9w-5-pack/2330j http://www.screwfix.com/p/lap-gls-led-light-bulbs-white-bc-9...
tbrownaw 9y ago
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 9y ago
  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).
cjsuk 9y ago
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.
- Hydraulix989 9y ago
  I'd be shocked if the flicker went to 0% as this article seems to imply ("because LED flickering is even more pronounced, with the light dimming by 100% rather than the roughly 35% of fluorescent lamps") -- and I doubt the flicker for fluorescent lamps is at RMS. There's _gotta_ be at least a smoothing capacitor after the bridge rectifier (are they actually that cheap to omit one?!). I can't find a single LED driver circuit schematic online without the low pass filter.
  - justinjlynn 9y ago
    Often the first things to be cut in cut-rate gear are comfort/longevity features such as smoothing capacitors and protection circuits. Generally if it doesn't have an effect on the return rate, it gets cut out to slash costs.
- rhizome 9y ago
  the cheaper ones seem to have a blue/white tone whereas the expensive ones have a yellow/white tone and are warmer. This is just normal color temperature and both come in all price points. I have several warm bulbs I got at Target on clearance for $2/2. I think it's just that the warm cheap LEDs are usually sold out, so all that's left are the prison-colored ones.
  - cjsuk 9y ago
zkms 9y ago
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/e18f88d078a54622682528e496596192/misc/flickerfactsheet_doe.pdf http://www.usailighting.com/stuff/contentmgr/files/1/e18f88d... 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 9y ago
  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.
abainbridge 9y ago
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.
- torrent-of-ions 9y ago
  That is seriously annoying. Not only do they flicker, they are slightly blue as well. I have mistaken an Audi for an emergency vehicle in my rear view mirror on multiple occasions. I am sure that this is their plan. Such lights should be outlawed.
  - Shivetya 9y ago
    Now I have found that some mirrors on cars and even motorcycles can distort the reflected light to give blue points. combine with polarizing glasses and it becomes even more difficult to find the exact cause. now if viewing straight on without another element to distort the light, like polarized lenses; I would be interested if the reflector built into the headlamp assembly can cause an issue.
  - gargravarr 9y ago
    I've found the colour to be too close to emergency-vehicle blue as well, particularly if the car behind hits a bump and momentarily brings their headlights into my mirrors, it's almost exactly like the flash of emergency lights. I shouldn't have to be second-guessing whether there's an emergency vehicle behind me, I should be following my first instinct which is to ensure I'm not obstructing traffic. Not clearing out of the way for an Audi pulling a tonne to rocket past me.
kabes 9y ago
But then wouldn't our 60Hz screens have a much bigger impact on office workers than the lights above them?
- IshKebab 9y ago
  Screen backlights aren't turned on and off at 60 Hz.
- pvdebbe 9y ago
  The screens have separate backlight which is done with other technologies and if with leds, definitely with higher frequencies than 60 Hz.
- tech2 9y ago
  Screen refresh rate (rate that each image is replaced) is a lot different to the frequency of the PWM applied to the backlight. If the backlight were pulsing at 60Hz people would be _very_ upset.
- garaetjjte 9y ago
  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 9y ago
    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-measuring-screen-flickering.html http://commonemitter.blogspot.com/2017/06/lenovo-t500-measur...
amelius 9y ago
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-7-segment-led-displays-break-apart-when-i-brush-my-teeth https://electronics.stackexchange.com/questions/32675/why-do...
Rjevski 9y ago
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?
jonsen 9y ago
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.
gargravarr 9y ago
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 9y ago
  > 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.
gustavam 9y ago
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.

80 points by ValentineC 9y ago

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 9y ago
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.
- deleted 9y ago
  [deleted]
- Osmium 9y ago
  Yeah, I think my Ikea ones are phosphor, the Philips Hue are RGB though and still fine.
  - seanp2k2 9y ago
    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 9y ago
      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).
  - inferiorhuman 9y ago
    I went to LEDs in my apartment about two years ago. 3 Hue bulbs + hub, some 48" T8 LEDs, and some E26 Ikea bulbs. The Ikea bulbs are great, power on instantly and slowly fade off. The T8s take about 3/4 second to turn on, and are nice and bright (and a far cry from the power consumption of the T12 florescent bulbs they replaced). The Hue bulbs... well, one's developed a noisy transformer. Replacements are, what, $40? Meh. I like the Zigbee integration, but not $40 in two years worth of like. And the CRI of the Hue is just as bad (actually worse) than the other bulbs. Lesson learned, those Ikea bulbs are great.
    - Osmium 9y ago
      Not trying to sell Hue here, but their bulbs have gone through several iterations by now. They were one of the first big names to push consumer LED bulbs, I wouldn't be surprised if their earlier versions had flaws just by being new. But maybe not, I don't know. (Also their color bulbs are $40, but they have much cheaper white ones, and also an in-between model they call ambiance which are white but allow you to adjust color temperature)
  - pjc50 9y ago
    Yes, you can tell the Ikea ones aren't flickery because they have huge phosphor persistence - several seconds after being turned off.
ars 9y ago
I've had the opposite, no problem with florescent, but many LED's drive me crazy - I keep seeing a "speckle pattern" like what a laser makes. If I don't move it's ok, but as soon as I look around I see a pattern of black and white areas from LED light.

Neil44 9y ago

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 9y ago
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-9w-5-pack/2330j http://www.screwfix.com/p/lap-gls-led-light-bulbs-white-bc-9...

tbrownaw 9y ago

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 9y ago
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).

cjsuk 9y ago

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.

Hydraulix989 9y ago
I'd be shocked if the flicker went to 0% as this article seems to imply ("because LED flickering is even more pronounced, with the light dimming by 100% rather than the roughly 35% of fluorescent lamps") -- and I doubt the flicker for fluorescent lamps is at RMS. There's _gotta_ be at least a smoothing capacitor after the bridge rectifier (are they actually that cheap to omit one?!). I can't find a single LED driver circuit schematic online without the low pass filter.
- justinjlynn 9y ago
  Often the first things to be cut in cut-rate gear are comfort/longevity features such as smoothing capacitors and protection circuits. Generally if it doesn't have an effect on the return rate, it gets cut out to slash costs.
rhizome 9y ago
the cheaper ones seem to have a blue/white tone whereas the expensive ones have a yellow/white tone and are warmer. This is just normal color temperature and both come in all price points. I have several warm bulbs I got at Target on clearance for $2/2. I think it's just that the warm cheap LEDs are usually sold out, so all that's left are the prison-colored ones.
- cjsuk 9y ago

zkms 9y ago

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/e18f88d078a54622682528e496596192/misc/flickerfactsheet_doe.pdf http://www.usailighting.com/stuff/contentmgr/files/1/e18f88d... 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 9y ago
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.

abainbridge 9y ago

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.

torrent-of-ions 9y ago
That is seriously annoying. Not only do they flicker, they are slightly blue as well. I have mistaken an Audi for an emergency vehicle in my rear view mirror on multiple occasions. I am sure that this is their plan. Such lights should be outlawed.
- Shivetya 9y ago
  Now I have found that some mirrors on cars and even motorcycles can distort the reflected light to give blue points. combine with polarizing glasses and it becomes even more difficult to find the exact cause. now if viewing straight on without another element to distort the light, like polarized lenses; I would be interested if the reflector built into the headlamp assembly can cause an issue.
- gargravarr 9y ago
  I've found the colour to be too close to emergency-vehicle blue as well, particularly if the car behind hits a bump and momentarily brings their headlights into my mirrors, it's almost exactly like the flash of emergency lights. I shouldn't have to be second-guessing whether there's an emergency vehicle behind me, I should be following my first instinct which is to ensure I'm not obstructing traffic. Not clearing out of the way for an Audi pulling a tonne to rocket past me.

kabes 9y ago

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

IshKebab 9y ago
Screen backlights aren't turned on and off at 60 Hz.
pvdebbe 9y ago
The screens have separate backlight which is done with other technologies and if with leds, definitely with higher frequencies than 60 Hz.
tech2 9y ago
Screen refresh rate (rate that each image is replaced) is a lot different to the frequency of the PWM applied to the backlight. If the backlight were pulsing at 60Hz people would be _very_ upset.
garaetjjte 9y ago
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 9y ago
  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-measuring-screen-flickering.html http://commonemitter.blogspot.com/2017/06/lenovo-t500-measur...

amelius 9y ago

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

Rjevski 9y ago

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?

jonsen 9y ago

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.

gargravarr 9y ago

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 9y ago
> 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.

gustavam 9y ago

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.