Testing LEDs and Screens

Correlating flicker with my "LED" symptoms

How do my "LED" symptoms correlate with light and screen flicker and is there any safe flicker? 

During 2023, I bought a professional flicker meter and other instruments to measure flicker. I'm a scientist, so tried to apply basic scientific practice as I measured the flicker of lights that do and do not hurt me. I measured the flicker of hundreds of lights. I also measured the flicker of screens that trigger neurological symptoms for me slowly to quickly. This testing is described in detail in the following Powerpoints and the data was shared with the FDA Office of Radiological Health in November 2023, to my knowledge this is the first report correlating measurements of LED light and screen flicker with health impacts. In biological science, we must be skeptical of the import and universality of findings when n=1, but my hope is that this study will provide a roadmap for what should be done to analyze the relationship between flicker and health for more people. The links below are Google Slides versions of the PowerPoints to view online. These files as original PowerPoints (better quality) and the underlying raw data are also available here.













A few highlights are integrated below, but please view the PowerPoints for the complete analysis. I apologize for any typos and roughness in presentation - I'm choosing not to focus on editing since all screen use injures my brain.

Discussion of results

Before purchasing a flicker meter, my hypothesis was that the few LED lights that didn't seem to injure me were completely flicker-free and thus had lower % flicker than LED lights that do injure me. This hypothesis was based on my not being able to detect the flicker of LEDs that didn't seem to injure me with a slow-motion phone video, claims of lights being flicker-free on the Waveform website, and the apparent absence of flicker for a Philips bulb in a waveform posted on the LEDBenchmark website. There were also many LED lights that injured my brain that did have noticeable flicker in slow-motion videos.

My hypothesis was wrong. The LED lights that don't seem to injure me do in fact flicker. Not much, but they clearly do. Their % flicker (0.8%-1.1%) is higher than that of several LED lights that injure my brain. The story is more complicated than I had initially thought.

The graph below shows 0.05 seconds of the 1.1% flicker of the Philips LEDs I have used since 2013 and that have never noticeably harmed me.

In contrast, the light below (IKEA Lunnom Globe) has flicker that is 10 times lower (0.11%), but it caused concussion-like symptoms with brain fog during 2 hour of testing in 2023 (see .Lights_HealthData_Pt2_LowFlickerBulbTesting). Although it seems implausible that such ow flicker can hurt me, it does. There are several LED bulbs with flicker similar to this that also trigger concussion-like symptoms for me.

Before purchasing the meter, I already knew that the workplace LED lights that first caused me noticeable serious brain injury in the fall of 2018 (beginning with intense pain within seconds of first exposure) had flicker that I could barely detect on slow-motion video, but other LED lights that I had at home for years without consciously connecting subtle ill effects to the lights had very high flicker that was easy to detect on video. My measurement data suggest that it is too simplistic to assume that seemingly subtle flicker patterns can at most cause subtle harm and that extreme harm only results from extreme flicker. It is quite possible that different kinds of flicker might affect different biological targets or do so with different intensity. As a molecular biologist, I know through experience that one can never assume you understand how a biological system will behave - you have to test it. And if you make a subtle change, you have to test it again. We can't assume that the only possible biological effects of flicker will be visual and based on the brain's image formation. Often, reports from people like me that subtle flicker is causing harm are dismissed because it's assumed that we can't see it. I almost never notice seeing flicker, but I definitely feel its effects as pain and brain injury.

I suspect that there was something specific about the workplace LED flicker or the combination of flicker patterns to which I had been exposed by that point that caused the beginning of my extreme flicker sensitivity in the fall of 2018. Interestingly, the high-flicker LED light at home was on a side table shining on my right temple for 5 years, as I sat on the couch at night and lost the ability to concentrate while grading papers and increasingly got minor headaches. Now, the feeling of swelling in my head that is my most persistent LED symptom is concentrated in my right temple and all of my LED symptoms are on the right side. Could the high-flicker LED lamp have caused initial injury in my right temple that was then primed for an even more extreme response to the 2018 workplace LED lights?

The graph below shows 0.05 seconds of  the 36% flicker of the Cree LED that was in the lamp near the right side of my head for 5 years.After my exposure to the 2018 workplace LED lights, this Cree bulb started to exacerbate my LED symptoms and it was noticeably painful, so I removed it.

My data indicate that there are probably several factors contributing to the biological effects of flicker:


Random flicker might be better than regularly pulsed flicker. Candlelight flickers slowly, but it doesn't harm me and even makes my brain feel a little better when I'm recovering from LED injury. 

Candlelight flicker: 0.5 second

I have very little data about random flicker for LED lights, but it turns out that that the Philips LED bulbs I've used without harm for 10 years at home have a (1.1%) flicker pattern with semi-randomness within the periodic pattern. And perhaps more significantly, the fixture where they're installed has a very slightly unstable electrical supply that creates subtle random flicker at a slower rate than the flicker from the bulb. Perhaps this instability makes the light seem more like candlelight to the molecules in my brain.

Philips LED: 0.05 second

Philips LED: 0.05 second, zoomed y-axis: 

Notice that the 120 Hz zigzag pattern is broken occasionally by a larger, deeper zigzag. Notice that the small "bubbles" of light within each zigzag occur tor variable time periods.

Philips LED: 1 second: Note the random jumps up and down of the light over this long time scale.

Color-to-color flicker

Color-to-color flicker seems especially harmful. Many white LED lights have slightly red to slightly green flicker as shown in the consecutive 240 fps slow motion video frames below (notice the green-red-green-red change on the left side of the image). These lights quickly caused concussion-like symptoms for me.

I notice my neighbor's rainbow LED porch light more and find it more painful when it's programmed to alternately pulse its colors than when it pulses its colors concurrently.

This photo is a panning shot of an LED light that cycled through rainbow at an instant when the light appeared to be magenta. The red and blue LEDs in the bulb alternate their flickering (see Lights_HealthData_Pt3_Flicker_ThroughMyWindows_Public for more images using color filters).

Camera  shutter speed = 1/20 second

Blue flicker frequency = 16x20 = 320 Hz 

Red flicker frequency = 16x20 = 320 Hz 

These photos are of the same LED light when it was programmed to be constantly magenta. The red and blue LEDs in the bulb now flicker much more concurrently. Three of the photos were taken using blue, green, or red filters on the camera lens.

Camera  shutter speed = 1/30 second

Blue flicker frequency = 10x30 = ~300 Hz 

Red flicker frequency == 10x30 = ~300 Hz 

It feels like this light is less harmful when programmed this way than when colors flicker alternately.

I'm also harmed by screens faster and more severely when there's more color-to-color flicker. There is a lot of screen data indicating this, including that the least harmful screen that I can use in full color happens to have the most synchronous color flicker. On any screen, using Nightshift hurts me more. It turns out that on every screen I've tested, Nightshift works by flickering green subpixels somewhat more and flickering blue subpixels a lot more, thus reducing the average amount of green and blue light. The overall effect is to create much more color-to-color flicker, since the screen flickers between very red and somewhat more blue/green.

Any flicker might cause injury

Even if there isn't color-to-color flicker and even if there isn't LED light, flicker can cause injury. For example, an eInk screen used as a computer monitor has no backlight, the frontlight is off, and the pixels visibly flicker. This screen gives me "LED" symptoms. Data in Screens_HealthData_Pt5_OtherScreensAndSummary.

Why is incandescent light flicker so much safer than LED flicker?

Like me, many people with LED sensitivity report being able to tolerate incandescent lights much better than LEDs. Often, our claims are dismissed since there are LED lights with less flicker than incandescents that we claim are hurting us. It isn't known why sensitive people tend to tolerate incandescents much better than LEDs with comparable waveforms, but testing indicates that there are significant differences between incandescent lights and LED lights beyond flicker waveform shapes.   (1) LEDs often have significant color-to-color flicker while incandescent lights do not have any color-to-color flicker. All of the light from an incandescent bulb comes from the glow of the filament as it is heated. Thus all of the colors rise and fall in brightness concurrently as the filament heats and cools. Flicker data for incandescent lights using different color filters over the flicker meter supports this - all of the colors seem to have flicker waveforms that are the same. However, this is not the case for many of the LED lights tested. The LEDs can have different flicker patterns for different colors, producing color-to-color flicker. Sometimes the amount of color-to-color flicker is even obvious in slow-motion video frames. (2) Incandescent light is predominantly red and near-IR light while LED light not. It's quite possible that evolution might have supported some tolerance of red to IR flicker considering humans' use of firelight over many thousands of years. In contrast, the flicker of LED lights has little red and near-IR light and has a character that is completely novel. Research in photobiomodulation therapy (see below) indicates that there may be beneficial biological effects specifically of red and near-IR light. For example, red and near-IR light has been shown to speed wound healing, reduce inflammation, and has even been used to reduce long-term effects of brain injury.

The graphs below compare the flicker and light spectra for a GE 60 W A19 incandescent light bulb and a Par20 LED bulb sent to me from Signify as their choice for a potentially safe LED (it triggered concussion-like symptoms for me quickly). Flicker and light spectra were measured normally and also with blue, green, or red filters over the light meter's sensor.

Insights from photobiomodulation therapy: Are there non-visual biological effects of flickering light?

There is an increasing body of research from the field of photobiomodulation therapy, in which LED light shines through the skin as a medical treatment, that identifies many non-visual effects of light on cells, tissues, and complex systems. The wavelength (color) of light matters and whether the light is pulsed or constant (and how it is pulsed) matters in terms of which proteins are stimulated and the types of biological effects. Some of the biological effects last for a long time - at least weeks following several minutes of light treatment, suggesting that the light treatments might alter gene expression patterns.Insights from photobiomodulation therapy lend support to the hypothesis that the biological effects of flickering light might not all be strictly based on visual processing. It's pure speculation, but I think it's possible that certain flicker frequencies might create some kind of resonance in light-absorbing proteins that leads to abnormal signaling.Perhaps flickering light alters gene expression patterns (also a speculative hypothesis), explaining how a brief LED exposure can initiate weeks to months of concussion-like symptoms for people like me. The reviews below provide an overview of relevant research.

de Freitas LF, Hamblin MR. Proposed Mechanisms of Photobiomodulation or Low-Level Light Therapy. IEEE J Sel Top Quantum Electron. 2016 May-Jun;22(3):7000417. https://doi.org/10.1109/jstqe.2016.2561201  https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/28070154/

Hamblin MR. Shining light on the head: Photobiomodulation for brain disorders. BBA Clin. 2016 Oct 1;6:113-124. https://doi.org/10.1016/j.bbacli.2016.09.002

Hashmi JT, Huang YY, Sharma SK, Kurup DB, De Taboada L, Carroll JD, Hamblin MR. Effect of pulsing in low-level light therapy. Lasers Surg Med. 2010 Aug;42(6):450-66. https://doi.org/10.1002/lsm.20950  https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/20662021/

Salehpour F, Mahmoudi J, Kamari F, Sadigh-Eteghad S, Rasta SH, Hamblin MR. Brain Photobiomodulation Therapy: a Narrative Review. Mol Neurobiol. 2018 Aug;55(8):6601-6636. Epub 2018 Jan 11. https://doi.org/10.1007/s12035-017-0852-4  https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/29327206/

Zein R, Selting W, Hamblin MR. Review of light parameters and photobiomodulation efficacy: dive into complexity. J Biomed Opt. 2018 Dec;23(12):1-17. https://doi.org/10.1117/1.jbo.23.12.120901  https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/30550048/

LEDs flickering more as they fail

Since the 1920s, lighting manufacturers have been specifically engineering light bulbs to fail. This planned obsolescence is for the purpose of selling more light bulbs. (This sounds like just a conspiracy theory, but was due to a real collaboration by major lighting companies, known as the Phoebus Cartel to limit the lifespan of light bulbs to 1000 hours: https://www.newyorker.com/business/currency/the-l-e-d-quandary-why-theres-no-such-thing-as-built-to-last). The Waveform Centric Home bulbs that I used to the point of failure flickered more over time, with flicker increasing from 0.9% to 100% (at 120 Hz) as they reached failure. Eventually some of them were visibly blinking on and off a couple times a second. The failing bulbs rapidly triggered brain injury for me, even before they were visibly blinking. I have noticed other LED bulbs visibly blinking in my neighborhood in street lights and at construction sites, seemingly because they had failed. I don't know whether all LEDs fail in this way or whether it's only some LEDs.

I don't know whether invisibly flickering more as bulbs age or visibly blinking slowly on and off are purposely engineered effects or accidents of engineering. I don't know what the planned mechanism for LED failure might be, but the US Dept. of Energy website (https://www.energy.gov/eere/ssl/led-basics) says that LED bulbs decrease in brightness over time as they fail and 70% of original brightness is considered to be failure. Is this reduced brightness due to more flicker? A March 2023 article by Tom Scocca in New York Magazine discussed the problem of LED failure that included flickering or color changes (https://nymag.com/strategist/article/led-light-bulbs-investigation.html).

Flicker of Waveform Centric Home 300K bulbs that are unused or that have been used continuously for 2, 3, or 7 months. These bulbs do not noticeably harm me when they are new, but they start to cause concussion-like symptoms for me as they age and acquire more flicker.

Flicker of four additional Waveform Centric Home 300K bulbs that have been used continuously for  7 months. The bulb on the lower right is slowly blinking on and off.

Summary of light flicker testing:

Summary of screen flicker testing:

More Information

Pre 2023 data

For more data and analysis from before I obtained a flicker meter see Testing LEDs and Screens Before 2023.

Demographic statistics and relevant medical history:

Female, living in New York City

Highest level of education: PhD in Human Genetics and Molecular Biology.

Employed full-time in science education. My current job is low-stress.

No history of concussion. 

No history of sleep issues.

No anxiety or any mental health issue. 

No history of eye problems other than nearsightedness.

History of common migraine without aura.

Following the onset of LED symptoms in 2018, I consulted a neurologist who did an MRI, a neuro-ophthalmologist who did extensive tests of my eyes, and an optometrist. None of these experts detected any problem, except that the neuro-ophthalmologist detected peripheral blindness in my right eye in a visual field test during my first visit when the clinic LED lights triggered my symptoms, but did not detect it on a followup visit where I protected my eyes from the clinic LED lights. The neurologist did various tests of neurological function that did not detect any issues, but I had to wait so many months for an appointment, that I wasn't experiencing LED symptoms (except enhanced sensitivity to flicker) by the time I had the appointment.

Comparison of my common migraine symptoms and my LED-caused symptoms

Onset and frequency of occurrence

Location of headache:

Quality of headache:

In addition to the above headache pain/pressure that can last days to months after a significant LED exposure, there is also a sharper, more localized pain behind my right eye that is only present when I can actually see LED light or other flickering light. It stops immediately if the light is turned off. The intensity of this pain and the time until this pain starts once I am exposed to flickering light depends on my sensitivity level and on the intensity of the flicker, with time until pain onset ranging from immediate up to at most 20 minutes. I'm more sensitive and the pain starts faster and is more intense if I've recently been exposed to flickering light or have ongoing symptoms from a previous exposure. This pain was the most intense in the fall of 2018 - it kept getting more intense each work day while working under the flickering LED lights. When very intense, it had a very high-frequency vibrating quality on the order of hundreds to thousands of hertz. It felt like a dentist's drill was creating vibrating pain/pressure behind my eye. At that time, the sharp vibrating pain would start immediately when I entered the flickering LED light and would stop immediately if I left the flickering LED light. This pain was sharp like the feeling of lemon juice in a paper cut, and seemed somewhat distracting, but wasn't debilitating in the way that common migraine headache pain is debilitating for me. 

Headache pain intensity

Is the headache aggravated by routine physical activity?

Is there nausea or vomiting?

Is there photophobia (sensitivity to light) or phonophobia (sensitivity to sound)?

I have become more sensitive to flickering light since the 2018 symptom onset. Beginning with a 3-hour exposure to flickering LEDs in April 2021, I have become sensitive to the flicker of some incandescent lights when I already have LED symptoms (causing mild pain and/or nausea) and have become more sensitive to the flicker of fluorescent lights. Sunlight and completely flicker-free LEDs have never caused or exacerbated my LED symptoms. I do not experience phonophobia.

Other secondary neurological effects?

I have significant alterations to my sleep patterns with hypersomnia in the first day or two following a serious flicker exposure and insomnia for weeks to months following that. For example, I'll tend to fall asleep very early (~6pm) in the first couple of days following a serious exposure. Then a few days later, I'll start to wake up in the middle of the night or early morning and be unable to fall back asleep for hours. This happens every night for weeks to months. I'm not feeling anxious and my mind isn't racing. I just can't fall back asleep. I'm not waking up due to pain - the pain is usually lessened when I wake up. The inability to get enough sleep at night, along with my inability to eat properly due to ongoing nausea, contributes to extra daytime fatigue. When I don't have LED symptoms, it's quite rare for me to have any trouble sleeping at night. 

In addition to the symptoms already described, another common symptom is a slightly swollen right upper eyelid. It is slightly difficult to open completely - the eyelid seems very slightly puffy and the space into which it needs to fold feels too tight. When the eyelid feels most swollen, wearing gas-permeable contacts tends to irritate it and sticky mucus collects in the eye if wearing the contacts (I wore contacts one such day then stopped because of the irritation to the inner surface of the eyelid). 

On about half a dozen occasions, I've experienced transient, but severe central vision blurriness in my right eye that lasts about a minute. It seems like there's a film partially obscuring my vision, but there isn't any mucus obscuring my vision - rubbing the eye doesn't change anything and the blurriness just goes away on its own within about a minute. 

The neuro-ophthalmologist who had flickering LEDs in the new office detected peripheral blindness in my right eye in a visual field test. This was before he dilated my eyes. When I returned the next week to repeat the test, but protected my eyes from the clinic light, I did not have any blindness. 

Out of the many months that I've experienced LED symptoms, there have been a few days that the symptoms have been most intense and that additional symptoms have occurred. These additional symptoms include my right temple becoming painful to the touch, the pain in the temple taking on a pounding quality, specific points on the right side of my scalp becoming painful to the touch, and an intensification of the feeling of tissue swelling around my right eye increasing to the point that it felt like there was pressure on the muscles controlling the movement of my right eye in its socket. In this case, these muscles hurt when reading a paper source and even when moving the eyes with my eyes closed. This is the only time I've experienced "eyestrain," and it only happened on about 2 days overall. 

Since the significant flickering LED exposure in April 2021, I've experienced more common migraine episodes than usual. These have tended to occur around the time I've had a moderate re-exposure to flicker that's restarted some LED symptoms. I can't say for sure, but it's possible that LED symptoms might increase the likelihood of having common migraine symptoms too. Taking ibuprofen still stops the common migraine symptoms, but has no effect on the LED symptoms. I know common migraine symptoms are beginning on top of my LED symptoms when I feel a little pain in my left eye due to light in addition to the right eye pain, when any light source (including sunlight or flicker-free LED light) causes both left and right side eye pain, and when the headache begins to include the left side of my forehead.

I suspect that flicker causes neuroinflammation around my eye, leading to the eyelid puffiness and feeling of pressure around my eye. I suspect that it was only when this inflammation was most severe that moving my eye became painful. I suspect that flicker causes neuroinflammation in the trigeminal ganglion, leading to the pain and feeling of pressure in the temple. I suspect that sensitization in the thalamus leads to the allodynia and other symptoms that might involve the cortex or other parts of the brain.


Is there a connection between LED symptoms, flicker sensitivity, and "Long-Covid"-like postviral symptoms?

Davis, H.E., McCorkell, L., Vogel, J.M. et al. Long COVID: major findings, mechanisms and recommendations. Nat Rev Microbiol 21, 133–146 (2023). https://doi.org/10.1038/s41579-022-00846-2

How to detect flicker with a slow-motion phone video

Smartphone slow motion 240 frames per second video can detect 120 Hz flicker in the Americas). Note that some phones may now require a 3rd-party app to record true 240 fps video. My iPhone stutters the recording, obscuring flicker in the built-in Camera app and the info for the video says ~180 fps instead of 240 fps even if the app is set to 240 fps. Instead, I use the Moment app to record 240 fps video, but play it back in the built-in Photos app. Extreme brightness flicker and extreme color-to-color flicker can be detected.

(1/2 cycle per frame) x (240 frames per second) = 120 cycles per second = 120 Hz

The image below shows 6 consecutive frames from a slow-motion smart phone video filmed at 240 fps of the LED fixture that was in the common hallway of my apartment building from 2016 until we replaced the fixtures with nearly flicker-free LEDs in the summer of 2022 to eliminate the harmful health impact of the flickering LEDs; the entire frame is shown for each image. This pattern is typical of 120 Hz flicker, with a full cycle taking 2 frames, although the contrast between bright and dim varies for different lights with 120 Hz flicker. More subtle flicker may be difficult to notice when consecutive frames are placed side-by-side. The flicker for the light below is obviously visible if the slow motion video is played at the typical playback speed of 30 fps. I find the flicker when such videos are played to be quite painful and triggering of symptoms, so I have chosen to show consecutive frames, rather than the actual video, since the difference in brightness in consecutive frames is visible enough in this format.

Similar images and videos from an NYC Public school, the NYC Subway system, and a grocery store are shown on the Public Health Risks page.

The image below shows 4 consecutive frames from a slow-motion smart phone video filmed at 240 fps of the LED lights at the Blick Art Materials store at 6th Ave and 20th in NYC, filmed on April 23, 2022. These lights appear to be white when observed normally, but actually flicker between slightly red and slightly green whitish light at 120 Hz. Less than a minute in this light while wearing a hat and shade 5 welding glasses triggered a headache behind my right eye (mostly pain without much pressure) and nausea with loss of appetite that lasted at least 6 hours, until I fell asleep. Note that data in the Powerpoints at the top of this page suggests that color-to-color flicker may be especially harmful for me, perhaps explaining the toxicity of these lights.

The flicker of the color-changing LED device below is even more complex. The flicker seems slower than 120 Hz. although it's hard for me to figure out how many frames constitute a cycle, partly because the device is continually changing colors, so the time that individual colors are displayed varies. This device was very triggering of my symptoms. The image shows 21 consecutive frames from a slow-motion smart phone video filmed at 240 fps; frames are slightly cropped around the device. Notice how the frames with 2 colors show how the smart phone records each slow-motion frame by scanning from one long side of the image to the other long side, with the color changing while the scan is in progress in some cases.

(6.5 cycles per frame) x (240 frames per second) = 1560 cycles per second = 1560 Hz

The images below show the very subtle flicker from the LED strip lighting that triggered my months-long symptoms in 2018. This was the first time, at age 42, that lighting had caused severe headaches and other neurological symptoms for me. Each of the 2 panels shows 6 consecutive frames from a slow-motion smart phone video filmed at 240 fps. The entire image for the first frame is shown, then only the rightmost portion of each of the next 5 frames is shown to the right side of the preceding frame. The vertical lines between the 2 panels indicate the divisions between the frames. The top panel shows the original images. The left portion of the frame shows the LED strip through a gap in the covering diffuser panels. The right portion of the frame shows a diffuser panel that is covering additional LEDs in the strip. The bottom panel shows the same images as the top panel, except that the images have been enhanced together in Photoshop to maximize the visibility of the horizontal bands that are parallel to the long edges of the frames. In the original video, very subtle bands of increased brightness seem to move across the screen as the slow motion video is played back. This is an example of the flicker percent being about at the limit of what can be detected using a smart phone. I see between 6 and 7 bands across the frame, which would indicate that the frequency of the flicker is about 1500 Hz, as calculated above. However, the data I provide for these lights in the graph above and in the linked spreadsheet lists 1000 Hz because that was the highest frequency setting for these lights for which a lighting analyst provided statistics. There are other examples of LED strip lighting that cause my symptoms, but for which I haven't been able to detect the flicker with a smart phone, although measurements from lighting analysts show flicker.

Sometimes the banding may be much more obvious if the dim phase of the flicker is dimmer, such as in this image of a color-changing LED device. This following image shows one complete frame from a 240 fps smartphone video. This is the original image except that a black rectangle covers a portion of the image; the colors and contrast have not been enhanced. There are 5 cycles of banding visible over the device and probably a similar number of bands over the other parts of the frame. So if there are about 10 cycles of banding, (10 cycles/frame) x (240 frames/second) = about 2400 cycles/second = ~2400 Hz for the flicker frequency.

Note that if you are attempting to detect very fast flicker with an iPhone, the banding will be parallel to the longer side of the phone. I didn't realize this when I first started testing lights in 2018, but one should ideally orient the phone so that an LED strip light spans the short distance across the phone (from left to right, rather than from top to bottom) so that you have a chance of observing the banding pattern as a variation in brightness, either across the strip light or across a part of the ceiling that is approximately evenly illuminated. Orienting the phone in the other direction, which is the more intuitive way that maximizes the length of the light in the video, makes it nearly impossible to observe the banding because there isn't a region of approximately uniform brightness in which to look for brightness variation. Focusing the camera on the brightest part of the light can help to maximize the contrast in the images. The banding pattern is generally more visible for a dimmed strip light than for a strip light at full brightness; see Background: LED Lights for a discussion of dimming strategies for LED strip lights, which often introduce or enhance flicker.

Lessons from mistakes in flicker testing:

From my perspective as a scientist, this seems obvious. However, when working with a lighting consultant, I realized that this was not their standard practice. They tended to have all of the lights on and then they'd hold a handhold meter up near individual light sources. This probably is fine under most circumstances, but when trying to obtain data about lights that are flicker-free or have very low flicker, other lights with higher flicker in the vicinity can contaminate the tests of the lights with low flicker.