What Is PWM Dimming and Why It Affects Your Eyes?

Описание: The Invisible Flicker
Welcome to the deep dive on digital displays. Today, we're dissecting an unseen technology that may be impacting your health: Pulse Width Modulation, or PWM dimming. We’ll explore exactly what this invisible flicker is, why manufacturers rely on it, and its often-overlooked effects on your visual comfort.
Pulse Width Modulation (PWM)
At its core, PWM is a digital trick. Most modern displays, especially OLEDs, cannot adjust brightness by simply lowering voltage. To simulate dimming, the screen rapidly cycles between being fully ON and fully OFF. Your brain integrates these cycles together, interpreting the reduced illumination as lower brightness, but those constant "off" periods are the fundamental source of the flicker.
The Duty Cycle
The level of dimming is precisely controlled by the Duty Cycle. This metric is the percentage of time the screen spends in the ON state during one full cycle. At 100% brightness, the cycle is fully ON. Critically, as you lower the brightness, the duration of the “off” period widens significantly. This dramatic increase in darkness gaps is where sensitive users start experiencing the most severe symptoms.
Why Manufacturers Use PWM
Despite the side effects, manufacturers favor PWM for solid technical reasons. First, it ensures superior Color Accuracy, allowing sub-pixels to run at optimal voltage. Second, PWM controllers are highly efficient for Cost and Design, simplifying complex driver circuits. Finally, it adheres to essential OLED Physics, preventing uneven lighting, or “mura,” which occurs when trying to regulate extremely low DC current.
The Stroboscopic Effect
Even if the flicker is too fast for your conscious brain to detect, it creates what is known as the Stroboscopic Effect. You can test this: if you move your eyes or wave an object quickly across the screen, you'll see a distinct trail of multiple, ghostly images—a "phantom array." This visual anomaly is a clear indicator that the display is rapidly blinking, even when it appears perfectly steady.
Biological Impact
The major concern here is the biological impact. Your brain’s visual cortex works overtime trying to constantly integrate those rapid shifts in luminance. Furthermore, the muscles in your iris may be forced to micro-adjust constantly in response to the light pulses. The resulting physical symptoms are unmistakable: severe Eye Strain, persistent Headaches, and even feelings of Nausea, similar to mild motion sickness.
Who Is Affected?
This isn't a universal issue, but it’s significant. Research indicates that approximately 10% to 15% of the population is highly sensitive to Temporal Light Modulation. For this minority, low-frequency PWM screens can, regrettably, be unusable, often forcing them to specifically seek out alternative display technologies, such as certain LCD panels or certified flicker-free OLEDs.
Frequency Matters: The Hz Race
The key to mitigation is frequency. The rate at which the screen cycles, measured in Hertz, dictates the risk. Older OLEDs often use low-frequency PWM, around 240 to 480 Hertz, which falls into a High Risk zone. Modern displays, marketed as "Eye-Care," are pushing this modulation frequency up to 1920, 3840, or even higher, moving the flicker beyond the physical and biological limits of human perception.
The Alternative: DC Dimming
The primary alternative is Direct Current Dimming. Instead of cycling on and off, DC dimming manages brightness by directly regulating the current supplied to the LEDs, offering a constant, steady stream of light with zero flicker. The trade-off? At extremely low brightness, the colors can become less accurate, and blacks can appear uneven or muddy—a common visual artifact sometimes termed "mura."
IEEE 1789 Standard
For technical guidance on safety, we look to the IEEE 1789 Standard. This defines accepted safety practices. Any frequency above 3000 Hertz is considered No Effect, safe for all users. Frequencies between 1250 and 3000 Hertz are Low Risk, though sensitive users may still feel slight fatigue. Crucially, any frequency below 1250 Hertz falls into the High Risk category, directly correlating with headaches and pronounced stroboscopic effects.
Mitigation Tips
If you own a device with PWM, there are steps you can take. First, always Keep Brightness High, as PWM typically slows down below 50% brightness. Second, check your developer options for an "Anti-Flicker" or DC Dimming setting. Third, always Use Bias Lighting; ambient light in the room helps mask the perceived flicker. Finally, when purchasing new hardware, look for high-Hz PWM specs or TÜV Rheinland Flicker Free certification.
Questions?
Understanding PWM is crucial for digital health and display technology selection. We hope this presentation empowers you to protect your eyes in the digital age. Thank you for your time. Feel free to reach out with any further questions.