Understanding PWM Flicker in High-Refresh-Rate Displays

Most modern smartphones use OLED panels, which control brightness through pulse-width modulation (PWM). Instead of continuously supplying power, the screen rapidly switches on and off at a certain frequency. At low brightness levels, the duty cycle shrinks, causing the display to flicker more noticeably. High refresh rates—90Hz, 120Hz, or even 144Hz—do not automatically eliminate this flicker; they often change the timing of the PWM pulses, but the fundamental on-off switching remains. When the refresh rate increases, the PWM frequency may be tied to or decoupled from the refresh rate, leading to unpredictable beat frequencies or sub-harmonic flicker that can be especially bothersome to sensitive users. Some devices use a higher PWM rate, such as 480Hz or 960Hz, to reduce visible flicker, yet many still fall short of the 1250Hz threshold considered safe by the IEEE. Furthermore, the interaction between high refresh and variable refresh rate (VRR) can cause the PWM frequency to shift dynamically, creating inconsistent strobing effects. Users often report eye strain, headaches, and dry eyes after prolonged sessions on such screens. Understanding the technical mechanism is crucial because the issue is not merely about refresh rate or brightness; it is about how the display's temporal light modulation interacts with human visual perception. A higher refresh rate can actually make flicker more perceptible in some scrolling contexts, because the content moves smoothly while the backlight flickers at a different frequency, producing a stroboscopic artifact. This fundamental mismatch between refresh and modulation is the root of the problem.

Why Eye Comfort Mode Falls Short on Modern Smartphones

Eye comfort modes, often marketed as “DC dimming” or “low blue light” features, aim to reduce visual discomfort. However, their effectiveness on high-refresh OLED screens is limited. DC dimming attempts to regulate brightness by varying the current rather than pulsing the display, which can eliminate PWM flicker. But in practice, many phones only activate DC dimming at high brightness levels, or they sacrifice color accuracy and contrast when enabled. At low brightness, the display may revert to PWM because the low-current approach causes mura and tint uniformity issues. Meanwhile, blue light filtering only adjusts the color temperature, not the temporal flicker. Even a warm-toned screen can still pulse at low frequencies, causing invisible but biologically active modulation. Some eye comfort modes also introduce systematic blur or response time degradation when attempting to smooth out the PWM waveform, which defeats the purpose of a high refresh rate. Another major shortcoming is the lack of adaptive behavior: the eye comfort mode is usually a static toggle rather than a dynamic system that monitors ambient light, content type, refresh rate, and user fatigue. For instance, a user reading text in a dark room at 120Hz with 20% brightness still faces severe PWM flicker, while the phone proudly displays an eye-care icon. Manufacturers need to integrate PWM frequency control into the display driver and allow users to choose a comfortable frequency, but many current implementations are superficial software patches that fail to address the root cause. Until eye comfort mode operates at the hardware timing level and actively adjusts the modulation frequency and duty cycle in real time, it will remain a marketing label rather than a genuine health solution.

The Trade-Off Between Smoothness and Visual Health

The push for higher refresh rates has dominated smartphone marketing, with 120Hz now standard on mid-range devices and 165Hz appearing on gaming phones. Yet this race for smoothness has a hidden cost: temporal dithering and flicker. In many high-refresh OLED panels, the PWM frequency is only slightly higher than the refresh rate, such as 120Hz refresh with 480Hz PWM. This creates a complex beat pattern that the human eye and brain must process. While some individuals perceive fluid animations as more comfortable, a significant portion of the population experiences migraines, nausea, or vertigo after short exposure. Studies on photosensitive epilepsy have long warned about flashing lights in the 10-60Hz range, but modern PWM flicker at 240-960Hz is not harmless either—it can still cause autonomic nervous system responses, pupil oscillation, and accommodation spasms, even if not consciously visible. The conflict between smoothness and visual health is not inherent; it exists because manufacturers prioritize motion clarity metrics over human factors. High refresh rates expose the flicker more clearly during smooth motion, especially in fast-paced games or when scrolling long documents. Users then face a cruel choice: disable the high refresh rate to reduce eye strain, or endure the discomfort for smoother interactions. This trade-off should not be forced upon consumers. A well-engineered display should offer both high refresh and flicker-free operation simultaneously. The industry needs to embrace alternative technologies such as liquid crystal modulation for backlighting, or advanced TFT driving schemes that maintain brightness through multiple sub-cycles rather than simple pulse cutting. Until then, every flagship phone is a compromise between visual performance and visual health, and the “high refresh” feature can become a liability for sensitive users.

Future Solutions: Toward Flicker-Free High Refresh Screens

The path forward lies in reinventing brightness control and refresh synchronization. One promising approach is continuous-on modulation, where the OLED emits light in short, high-frequency bursts that exceed the critical flicker fusion threshold of 2500Hz. Samsung and LG have demonstrated displays with PWM frequencies up to 6000Hz, but power consumption and driver IC complexity remain barriers. Another solution is duty-ratio correction combined with ambient-light feedback: when the phone detects low ambient brightness, it automatically shifts to a higher PWM frequency and a lower duty cycle, ensuring flicker remains imperceptible. More advanced techniques include hybrid dimming, which mixes current-based dimming for low luminance and pulse-based dimming for high luminance, avoiding the low-brightness flicker trap. Additionally, the refresh rate itself can be dynamically uncoupled from the backlight frequency. For example, a 120Hz refresh display can use a fixed 2400Hz PWM clock independent of the frame rate, eliminating beat flicker entirely. Manufacturers should also adopt open standards under the IEEE 1789 guidelines, clearly listing PWM frequencies in device specifications so consumers can make informed choices. Eye comfort modes should evolve into “temporal health profiles” that access the display driver’s timing registers and allow granular user adjustments, from 480Hz to 10000Hz. While regular software updates can improve sensor algorithms, the core fix requires silicon-level redesigns and closer collaboration between SoC vendors, panel makers, and OEMs. The future is not about abandoning high refresh rates, but about making the refresh process genuinely flicker-free. Once that is achieved, smoothness and visual health will no longer be competing priorities, and users can enjoy their phones without hidden headaches.