Light Flicker is Stressing Us All Out

§Introduction

If you had to describe modern society in one single word, what would it be? It would be tough to pick just one, but where my mind goes is the following: activated, over-stimulated, desensitized. I think there are very few individuals, if any at all, who cannot relate to the feeling of the words that I just listed out. For most, it is an all too familiar state of being. These feelings have always existed, but in my opinion, never to the degree of prevalence that they do now. Our nervous systems are collectively “cooked”, and I think it is of utmost importance to understand why that is happening.

There are many reasons of course, but I believe that distinct elements of our day to day environment are the main culprit. One specific element that is a potent stressor to our body and activator of our nervous system is light flicker. Light flicker is in my opinion one of the most under discussed environmental stressors and one that is so mind-numbingly frustrating as to why it even exists in the first place…that it is worth hammering awareness on this topic until changes are made.

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Light flicker can be defined as a rapid and repeated change or modulation in the intensity (or brightness) of light over time (IEEE - PAR1789). It is easy to grasp the concept of flickering light when the light flicker is visible to the naked eye (ie a strobe light), but the real problem arises when flicker is invisible to our eyes yet perceivable by our brains, eyes, and nervous system. This is the flicker that we need to fix.

There are two main types of light flicker that we are exposed to on a daily basis that I will focus on: that from lights and that from screens. They flicker for different reasons, but both have a negative impact on our biology.

§Overview

1. Flicker from lights

   1. A result of our 50/60Hz AC electrical power grid (AC ripple).
   2. Far worse in cheap LEDs vs filament lights.
   3. Avoidable with higher quality bulbs/electronic design.

2. Flicker from screens

   1. A result of engineering optimization for controlling brightness.
   2. “Pulsed Width Modulation” (PWM) dimming is the main culprit.
   3. Avoidable in consumer hardware design, but extremely hard to find phones that don’t use PWM dimming at problematic frequencies.

§Flicker from Lights (LEDs and AC Power)

Flickering lights are everywhere. Light bulbs, car headlights, street lights. LEDs are especially problematic. Most lights today seem innocent, aside from their overbearing blue dominant light spectrum…yet the slow motion camera reveals the truth about the lights in real time. No research paper should be required for you to understand that this is probably not good for your brain (will share same later for the “need to see the science” stans), and also for you to surmise that this could be a probable cause of cellular energy drain if you were to sit under lights like these for 8-12 hours/day.

Try yourself: if you have a newer smartphone and the slow mode is at least 240fps you should be able to capture a “bad flickering LED”. If you have a 480 or 980fps camera…you’ll be blown away at what you can capture (try your phone screen also).

So why do our modern LED light sources flicker to such a bad degree? Ironically enough it is not the sole blame of the cheap, highly commoditized LED bulbs/fixtures themselves…but rather combining cheap electronics with an AC power grid.

The issues:

1. The nature of our grid is that it provides alternating current (AC), which oscillates in amplitude at 60Hz or 60 times per second. This creates modulation in a light source at two times the frequency (120Hz).
2. LEDs run off of direct current (DC), so in order to power them up we need to take our 60Hz (or 50Hz internationally) AC power and convert it into DC. This conversion process does not happen perfectly (especially with the cheap power electronics in most LEDs), so the result is AC “ripple” current** riding on top of the DC current that creates an even higher amount of light modulation or flicker.
3. LEDs are a semi-conductive material, so they power on instantaneously - meaning they bare the full brunt of the light modulation. Filament bulbs (incandescents) have a “thermal inertia” since they are a heating element, that blunts the effect of the AC ripple and thus lowers the light modulation output quite significantly.
4. High quality or “low to no flicker” LEDs contain passive components to “smooth” this AC ripple, minimizing the effect of its highly variable input signal to whatever device it is powering. Cheap LED bulbs or fixtures skip investing into components that do this because of how cost competitive the market is.

This entire situation is ironic because LEDs were touted as the modern upgrade to fluorescent lighting (especially in the commercial market), and they actually flicker far worse than a modern fluorescent fixture. Old fluorescents used to flicker very bad because of a magnetic ballast design (also at 120Hz), but those were pretty much phased out over 20 years ago.

Spectrometer plot showing light modulation of a white LED

§Flicker from Screens (PWM Dimming)

There are a few different characteristics of a modern electronic display (aka screen) that cause flicker, but the main culprit is something called “PWM dimming”. PWM (Pulse Width Modulation) is an electronics control mechanism that uses pulsed signals as the LED driver function to control the brightness of the device display.

PWM dimming has become the standard way to drive LEDs because it has specific advantages when it comes to retaining color consistency at lower brightness, and it typically is more power consumption efficient. In a PWM dimming application, the diodes are being modulated to turn on and off very rapidly (faster than our eyes can perceive) to reduce the overall appearance of brightness of the light emission of the LEDs (aka luminance).

The lower the brightness setting, the longer the “off time”. The “duty cycle” refers to the ratio of the LED being modulated “on” vs the total period of the cycle. Higher screen brightness setting = higher % duty cycle = more “time on” for the LED. This can be visualized in the graphic below.

PWM Display luminance plot showing the change in light output over time

As a result we have to look at smartphone screens as shown in the above videos. Not only that either, as because the peak luminance of a PWM dimmed LED stays the same and only the duty cycle changes, that means our eyes are exposed to the same peak intensity of light at night vs during the day even if we changed the “brightness” setting on our phone. Only the perceived brightness is lower.

Screen flicker, coupled with the blue light dominant light spectrum of screens, is why looking at your phone right before bed is highly disruptive to our sleep (and thus our overall health).

§PWM Flicker on OLED screens vs LCD screens

Not all PWM flicker is created equal. The flicker frequency used for PWM dimming is directly related to how potentially stressful it can be to our eyes and brains. It is well agreed upon that the lower the frequency is, the more it can stress us out and cause eye strain. This is because at a high enough frequency, the oscillations are happening so rapidly that your brain basically perceives them as a continuous signal.

The “risk factor” of flicker is also dependent on the modulation % (similar to duty cycle) of the flicker as well, but since we all use our devices across different brightness settings and modulation % ‘s, it is best to focus on the frequency as the independent variable in our control.

Up to and including the iPhone 11, liquid crystal displays (LCD) were the standard for smartphones. A big switch was made to OLED display technology and the tech giants have never looked back. When it comes to PWM dimming frequency, there was a big shift when this swap occurred:

• Most LCD display use a PWM frequency of 1000Hz+ or no PWM at all.
• Nearly all OLED smartphone use a PWM frequency of 240Hz or 480Hz.

(This is due to the OLEDs being controlled as singular pixels, and thus needing lower PWM frequency to maintain that extremely precise color consistenecy at lower brightness settings).

§The Impact of Light Flicker on our Health

Most people don’t realize it, but light flicker is one of the most pervasive biological stressors in modern life. From office lighting to smartphone screens, we’re exposed constantly. Both electrical engineers and biological scientists agree it can cause:

• Headaches, eye strain, blurred vision and migraines
• Aggravation of autism symptoms in children

This is documented in the Institute of Electrical and Electronics Engineers (IEEE) 1789 standard for best practice in LED lighting applications, amongst other scientific reviews.

The P1789 committee from IEEE identified the following major effects of flicker:

• Photo epilepsy
• Stroboscopic effect
• Increased repetitive behavior among people suffering from autism
• Migraine or intense paroxysmal headache
• Asthenopia (eye strain); including fatigue, blurred vision, headache and diminished sight-related task performance
• Anxiety, panic attacks
• Vertigo

The side effects are directly in line with what one would experience during, or at the end of a long work day looking at a computer display or a smartphone screen.I have found that light flicker is extremely activating to our nervous system, and thus keeps us stuck in “fight or flight”, which downstream can lead to a whole slew of other health issues.

When your body and nervous system is activated chronically, there are two main negative repercussions:

1. Your body burns through energy at an accelerated rate - depleting you at a biological level.
2. Cellular repair shuts down - inhibiting your body’s ability to recover and heal.

Chronic nervous system activation is the hallmark of our modern world, and an ever present threat to our physical health and human psyche. Overstimulated, drained and desensitized is the antithesis of peak human experience…and it compromises your cellular health in the long run.

The cellular impact of stress on energy metabolism.

Light flicker is an unnecessary evil. One that quietly drains your vital biological energy and disrupts your parasympathetic nervous system. Thankfully, it can be avoided to some degree. Here’s how to take back control.

§How to Minimize Your Flicker Exposure

It is impossible to fully avoid light flicker, especially if you work a 9-5 in a typical commercial office building and use a modern smartphone. So here is a list of what I think are the most meaningful tips to minimize light flicker and its impact on your health - focusing on your at home light environment + personal device usage.

• Swap your at home lights for flicker free LEDs or incandescent bulbs. You can test with the slow motion camera on your phone.
• Avoid going to notorious high flicker commercial light places (grocery stores, gyms, etc.) late at night.
• Minimize screen time to the best of your ability.
• Use your laptop in place of your phone as much as you possibly can.
• Consider a swap to devices that use DC dimming by default (Daylight Computer or iPhone 11) - or high frequency PWM (Xiaomi phones, Nothing phone, etc.).

PWM dimming is why we made Daylight Computer DC dimming and flicker free from the start. You can also read more in depth about screen flicker on our site.

§My Low Flicker Lifestyle

As someone who is extremely sensitive to light flicker due to my history of concussions, I have a very curated light environment that is low flicker to the highest degree. This is also because I get a headache after looking at a PWM dimming OLED smartphone after 60-90 seconds (not kidding).

• iPhone 11 as my daily driver smartphone

• Investigating TCL Nxtpaper 60 and LCD swapped iPhone 15 pro as 2nd/better phone options

  • TCL is Android and not native to work in US
  • Early data on 2nd version of iPhone 15 Pro w/ LCD is promising! (more in depth coming very soon on this)

• Use my MacBook + Daylight for 90% of my screen time (try to avoid phone time)

• Late night work on an incandescent backlit monitor

• Work outside as much as possible

• Halogen + incandescent lights indoors, as well as candles at night time

  • Read my popular substack article on Incandescents vs LEDs which discusses flicker

I find it much easier to regulate my nervous system when I am in a low flicker environment. I know that others would benefit greatly from that switch as well.

Working outdoors is the ultimate low flicker environment

We need to demand lower flicker / less PWM on our phones and less flicker in LED based lighting solutions as the default. It is completely unnecessary and is having a profound, negative impact on humanity. We did not consent to this, and in our already over-stimulating and stressful modern world nobody should need to consciously worry about light flicker.

(Be warned, if you do swap out your home lighting and screens to be low flicker - going back in a high flicker environment will be telling. I rest assured that your nervous system will thank you. As will those closest to you).

-Tristan

§Flicker Research Studies:

§1) Potential Biological and Ecological Effects of Flickering Artificial Light

§2) PMCLight Emitting Diode Lighting Flicker, its Impact on Health and the Need to Minimise it

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