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:
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:
Fortunately, there are better alternatives to this constant flicker.
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:
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:
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.
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.
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.
This post is part of a continuing series on Calm Tech certification standards.
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