Why Some LED Lights Feel Uncomfortable: Understanding PWM Flicker and Better Alternatives

I recently spent a few weeks running a conference for a community of researchers and writers in a historic chateau in the French countryside. During this time, I also examined the history of the building and how texture, size and proportionality affected thinking in the space.

This experience turned out to be a perfect illustration of how some modern lighting choices can disrupt our experiences in places as beautiful as this.

This beautiful French chateau hosts a community of writers, artists and philosophers in the wintertime, and weddings in the summer. It’s been marvelously restored through a lot of love and hard work.

The Chateau was built in the 1650s on top of a hill overlooking a village of ~400 people in the countryside outside of Paris. During the day, all of the rooms were stunning, but at night, some of them began to feel uncomfortable.

One of the Chateau’s rooms in natural light.

In the past, this room might have been lit by the warm glow of candlelight or a warm incandescent lightbulb on a 100 year old chandelier. But now, like many historic buildings, analog bulbs had been replaced with LED lights for practical reasons; consistent brightness and reduced energy bills.

One room in particular felt worse than the others. I took my camera around to see why.

In my experience at the chateau, the room felt uncomfortable despite the warm light. Others in the group reported similar feelings, though individual sensitivity to flicker varies widely. My camera told the story clearly:

The telltale signs of flickering lights — big bands of dark and light that show up on a camera.

The big bars of color came from modern LED lights fitted into the ceiling chandelier. My camera captured what my eyes couldn’t quite detect: thick bands of light and dark across the frame. The light wasn’t steady; the LEDs were flickering, pulsing on and off thousands of times per second to create the dimmed effect.

This explained the room’s uncomfortable atmosphere. Like many historic spaces, it had been “upgraded” with modern lighting that created an unwelcoming environment despite its warm appearance.

The truth is, most light sources flicker; very few people perceive it directly, but we still feel its effects. You may have noticed that some light bulbs emit a warm glow that somehow doesn’t feel cozy. Often, what we’re unconsciously reacting to is that subtle flicker.

It’s important to note that many people don’t consciously notice PWM flicker, and for most people, modern LED lighting poses no issues. However, for those who are sensitive, whether due to migraines, eye conditions, or individual variation, understanding these technical differences can be helpful.

The technical source of the issue is called pulse-width modulation (PWM), a method of controlling how much electricity a light source (in this case) receives at any given moment; it causes the light source to be off for a split second. Hence the flicker.

PWM is an often-used default for OLED digital displays (smart device screens, computer monitors, etc), LED lights, and some incandescent bulbs.

Flicker is all around us. We usually don’t see it, because our eyes are generally good at averaging out artificial light sources, similar to how we see a rapid series of individual images as a single moving picture. But it’s still a force that causes eye strain or discomfort.

Think of it like a soda dispenser. When you pour yourself a soda at a movie theater or fast food joint, it doesn’t usually dispense your selected brand. It’s cheaper for companies to store soda outside of the flavoring. So instead, what happens is the designated soda flavor “pulses” into the cup, mixing with the soda water.

This is more or less how we see PWM-based light — but in this analogy, our eyes are the cup! More advanced dimming systems pre-mix the light before sending it into your eyes. This greatly reduces eye-strain and makes for a much more comfortable long term experience.

And this is a process that usually happens to us during our entire waking day, forcing to process all the blinking on and off lights around us as a uniform experience. A significant minority of us — from 5% to 20% — have acute reactions to this flicker, up to and including migraines and nausea. There’s even a PWM Sensitive support group on Reddit!

Here’s a breakdown of PWM symptoms and their propensity:

*Up to 15–50% slower decision-making in offices with high flicker (and high CO₂)

Frustratingly, flicker is a problem that’s little discussed in public — but it is a key focus for us at the Calm Tech Institute. In the next section, let’s dive deeper into the science between the flicker, and summarize some of CTI’s recommendations for addressing it:

Inside PWM’s Flicker

Flicker and various dimming methods for lightbulbs.

This chart shows the difference of flicker intensity for various lightbulbs. To understand why PWM bulbs have so much flicker, imagine them being controlled by a robot arm flicking the on/off switch thousands of times per second. When you want bright light, the robot varies the time so the switch is in the “on” mode most of the time, and “off” only briefly (like 50% in the chart). Whereas when you want to dim the light, the robot arm puts the switch in “off” most of the time and “on” only briefly (like 6.25% in the chart).

Generally, our eyes can’t see the super-fast blinking during this process, and it just seems the light is getting dimmer or brighter. This is why PWM can cause so much discomfort: It’s commonly used in LED lights, OLED displays, and many smartphones, laptops, monitors, and TVs. Bulbs flickering below 1kHz are often perceptible to sensitive users, even if it’s not consciously noticed; the human eye can detect flicker as high as 2,000 Hz, especially in our peripheral vision.

Here are kHZ levels for various popular devices — many of them so low, they have high health risks:

Image courtesy of DayLightComputer.com.

Fortunately, there are better alternatives to this constant flicker.

Calm Tech Principles, CCR, and Lighting a Better Way Forward

Calm Tech Certified™ ranks products on their use of attention, periphery, robustness, light, sound and material use in an 81 point specification process. In our certification, Light is a top level category (CT4), with one goal being that illumination sources in the device under review meet a “Flicker Free” standard (CT 4.1.6).

One method for creating light dimming that’s easy on the eyes is called Constant Current Reduction, or (CCR). Calm Tech Institute scrutinizes device dimming methods, with the acceptable options being “CCR Dimming” or ensuring companies display the frequency of their PWM dimming as “High-Frequency PWM Dimming (XX kHz)”. Here’s a breakdown:

Image courtesy Daylight Computer Company

Dimming is done by lowering the current supplied to the LED, without switching it on/off rapidly. It’s commonly used in high-end or flicker-free lighting setups, such as medical and photography equipment. The absence of flicker significantly reduces risk of visual and neurological symptoms, and promotes visual comfort, especially for tasks requiring prolonged screen or light exposure.

In studies, the benefits for using Constant Circuit Reduction (CCR) are substantial:

Benefits to the human experience when using CCR or DC dimming vs. PWM

It’s important to note these advantages, since CCR bulbs tend to be more expensive. However, they should be treated as an investment in better well-being and enhanced life experience, both which have a positive effect on productivity.

Finding the Flicker: What to Look For in Lights Within Your Environment

Check PWM frequency, typically listed in the product specs. Anything under 5,000 Hz may still cause problems. Also look for: “Flicker-free” certification (e.g., TÜV Rheinland) or “High-frequency PWM” (above 20 kHz is considered safe for nearly all users). As discussed in the previous section, devices with “DC dimming” or “hybrid dimming” options are also good alternatives.

Calm Tech Certified™ Daylight Computer deliberately designed their computer with DC dimming in order to improve the experience for their customers.

Fortunately, product developers are beginning to apply these principles. Calm Tech Certified™ Daylight Computer, one of the first products to receive certification, focused on this aspect. They made the choice to deliberately remove PWM from their device display to make screen viewing a restful experience. The company’s reward is a passionate customer base: Its first models completely sold out their production run.

Whether PWM flicker affects you personally, understanding these technical differences can help you informed lighting choices. As LED technology continues to evolve, manufacturers are increasingly offering flicker-free options for those who need them.

This post is part of a continuing series on Calm Tech certification standards.

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