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If PWM flicker seems to trigger eye strain, shop for a phone whose display has independently measured, low-amplitude light modulation at the brightness levels you actually use. Check more than a “DC dimming” or “flicker-free” label: ask for measurements at low, medium and high brightness, including modulation frequency, modulation depth and waveform. Then test the exact regional model with your normal brightness, refresh rate and software settings during the return period. No display mode is proven to prevent or treat eye strain for every person.
Start with the measurements that matter
Display brightness is not always steady. A phone can regulate light by rapidly varying the electrical drive (PWM) or by changing the drive level more continuously (DC dimming). Your eyes may react to the resulting modulation even when the screen appears stable. Because sensitivity differs, the useful question is not “Which brand is safest?” but “How does this exact phone behave at my usual settings?”
- Modulation at low brightness: Ask for data near the dim level you use at night or in a dark room. Some panels change behavior substantially as brightness is reduced.
- Modulation at medium brightness: Include the level used for reading, messaging and indoor work. A phone that performs well at maximum brightness may use a different dimming scheme lower down.
- Frequency: Record how rapidly the light pattern repeats, in hertz (Hz). A higher number can reduce the visibility of some effects, but frequency alone does not describe the amount of light change.
- Modulation depth and waveform: The percentage swing between bright and dim portions, and the shape of that swing, indicate how strongly the light output changes. Reliable independent measurements should report these where possible.
- Exact configuration: Verify the regional model, panel variant, software version, refresh-rate setting and any eye-comfort or flicker-prevention option. A specification for one market or mode may not apply to another.
Independent laboratory results are more useful than a marketing term, but they still describe a particular unit and test setup. Treat them as evidence for comparison, not as a personal medical prediction.
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PWM and DC dimming are different control methods
How PWM works
Pulse-width modulation (PWM) keeps a light source near a chosen drive level and switches it on and off rapidly. The proportion of each cycle that is on—the duty cycle—sets the average brightness. A short on-time produces a dimmer average output, while the switching frequency determines how often the cycle repeats.
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A camera or light sensor can detect this variation even when you see a continuously lit image. The important variables are the frequency, the depth of the variation and the waveform. Two phones can both advertise “high-frequency PWM” yet produce different modulation amplitudes at the same brightness.
How DC dimming works
Direct-current (DC) dimming changes the supplied voltage or current to alter brightness instead of relying solely on on/off pulses. Xiaomi’s official support page describes the Xiaomi 15 this way: “The Xiaomi 15 adopts DC dimming, which is a method of adjusting screen brightness by controlling the power (voltage or current) supplied to the screen.” Xiaomi’s support explanation is a manufacturer feature statement, not an independent brightness-by-brightness measurement and not proof that the mode will relieve your symptoms.
Real phones can combine methods. A panel may use DC-like control over part of its range and switch to PWM at very low brightness, or offer a selectable mode that changes color, brightness or uniformity. Confirm the behavior of the exact model rather than assuming the label describes every setting.
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Why frequency alone is not a buying rule
Frequency is easy to quote, so it often dominates phone specifications. It should be one column in your comparison, not the verdict. A high-frequency signal can still have substantial modulation depth, and a lower-frequency signal with a smaller amplitude may affect people differently. Measurement equipment, test brightness and the point on the screen being measured also influence the result.
When a test report is available, look for a graph or table covering several brightness points. Note the measured frequency, percentage modulation or amplitude, and waveform. If the report gives only one number at maximum brightness, it cannot tell you what happens at your normal reading level. If a reviewer says “flicker-free” without describing the instrument, brightness and refresh-rate settings, treat the phrase as unverified marketing rather than a standardized result.
What current manufacturer claims actually say
Xiaomi 15: an advertised DC-dimming mode
Xiaomi states that the Xiaomi 15 uses DC dimming. The statement identifies the company’s intended brightness-control method, but the available public information does not provide independent measurements for every regional variant at each brightness setting. Before buying, check the phone’s display settings and ask whether the mode is active across the range you use. A store demonstration or a return-period test is more informative than assuming that every Xiaomi 15 behaves identically.
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HONOR: high-frequency PWM options with a refresh-rate condition
HONOR’s global eye-comfort page advertises ultra-high-frequency PWM dimming at 3,840, 4,320 and 5,280 Hz. HONOR qualifies the maximum 5,280 Hz figure: it is effective only when the screen is set to a 165 Hz refresh rate. Read that as a company claim tied to particular hardware and settings, not as an independent comfort certification. Verify the exact phone, country version and software controls before applying the figure to a retailer listing. The company also maintains a regional page, so specifications can differ by market: HONOR’s global technology page and its South Africa page should be checked against the model you can actually purchase.
What the independent evidence can—and cannot—tell you
The 2025 IEEE conference comparison
An IEEE Xplore record added on 2025-12-31 describes a short experiment in which participants performed 45-minute visual tasks on PWM- and DC-dimmed displays at 45–55 nits. The abstract reports that PWM dimming had a significantly greater impact on ocular imaging quality, while accommodative-convergence (ACC) testing found no statistically significant difference in visual-fatigue indices. Read the result narrowly: it is one study under stated conditions, not a ranking of every phone and not evidence that DC dimming prevents eye strain. The record is available at IEEE Xplore.
IEEE 1789 is guidance for LED current modulation, not a phone certificate
The IEEE Standards Association describes IEEE 1789-2015 as recommended practices for modulating current in high-brightness LEDs to mitigate potential health risks to viewers. Its page lists a publication date of 2015-06-05 and an inactivated date of 2026-03-26, with the status “inactive-reserved.” The document concerns LED modulation practice; it does not certify a particular smartphone panel or establish a universal safe threshold. See the status and scope at the IEEE 1789 page.
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A practical phone-comparison checklist
Use this checklist when shortlisting models or asking a retailer for details:
- Identify the exact model. Record the model number, sales region, panel type if listed, and current operating-system version. Regional substitutions can change the panel or available display modes.
- Find independent measurements. Prefer reports that name the instrument and show results at multiple brightness levels. Capture frequency, modulation depth or percentage modulation, and waveform information rather than a single “PWM rate.”
- Prioritize your real brightness range. If you normally use 10–30% brightness, measurements at 80–100% are not enough. Include a medium level for indoor work and a low level for evening use.
- Check the control in software. Look under the display or eye-comfort settings for labels such as DC dimming, flicker prevention or high-frequency PWM. Note whether enabling an option changes color temperature, maximum brightness, battery behavior or refresh-rate choices.
- Record refresh-rate interactions. A 120 or 165 Hz refresh rate describes image updates, not the dimming waveform. If a vendor ties a PWM mode to a particular refresh rate, verify that both settings can remain enabled together.
- Compare like with like. Put candidate phones at the same brightness, refresh rate, color mode and content. A bright white page and a dark interface can exercise the panel differently.
- Plan a return. Keep the packaging and confirm the seller’s return window before opening the phone. A personal trial is informative, but it is not a clinical test.
How to test a phone in a shop or during the return period
Set up a repeatable trial
- Disable automatic brightness temporarily and write down the brightness percentage or slider position.
- Test at the low level you use in bed or a dark room, then at your normal indoor level and a brighter outdoor level.
- Repeat the sequence with each available refresh-rate setting and with any DC-dimming or flicker-prevention option on and off.
- Use the same tasks for each setting: reading black text on white, scrolling, watching video and viewing a dark interface. Keep sessions short and take breaks.
- Note symptoms, timing and conditions in a simple log. Record whether discomfort appears immediately, after prolonged reading or only at a particular brightness.
This comparison cannot establish a diagnosis or guarantee future comfort. It can reveal whether one configuration feels better to you than another and whether a software option introduces an unacceptable color or brightness trade-off.
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When measurements and experience disagree
If a phone has impressive published numbers but feels uncomfortable, trust the repeatable personal result and return it if allowed. If it feels fine in a five-minute shop visit but causes symptoms during a longer session, the longer trial is the more relevant observation. Conversely, a brief reaction can come from glare, dry eyes, viewing distance, text size or room lighting rather than the panel’s modulation alone. Change one variable at a time so you can identify what matters.
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Trade-offs to check before choosing a mode
| Feature or claim | What it may change | Questions to ask |
|---|---|---|
| DC dimming | May reduce pulse-style modulation over part of the brightness range; color accuracy or minimum brightness can change on some panels. | At which brightness levels is it active? Is it enabled by default? Are independent measurements available? |
| High-frequency PWM | Raises the repetition rate of modulation; does not by itself specify modulation depth or waveform. | What are the measured depth and waveform at low and medium brightness? Is the quoted rate tied to a refresh-rate setting? |
| “Flicker-free” label | Usually a vendor-defined marketing description unless a test method is supplied. | Who measured it, with what instrument, at what brightness and refresh rate? |
| Higher refresh rate | Makes motion updates more frequent and can affect power use; it is separate from brightness dimming. | Does changing refresh rate alter the dimming mode or the quoted PWM behavior? |
| Eye-comfort filter | Often shifts color temperature or reduces blue content; it does not necessarily change light modulation. | Can the filter be enabled independently, and does it affect the brightness range you use? |
How to compare phones without overclaiming
Create a small record for each candidate rather than a single winner. List the low-, medium- and high-brightness measurements; the available dimming controls; the refresh-rate dependency; any color or brightness trade-off; and your own result during a consistent trial. Mark missing values as “not stated” instead of inferring them from a product label.
For example, the Xiaomi 15 has an official DC-dimming statement but no publicly supplied independent, brightness-by-brightness results for all regional variants in the available material. HONOR publishes specific high-frequency figures and a 165 Hz condition, but those figures remain company claims until independently measured for the exact device. Those two descriptions are not directly comparable until the same measurement method is applied.
If eye strain continues
Stop using a configuration that repeatedly causes discomfort, reduce glare and reflections, enlarge text, keep a comfortable viewing distance and take regular breaks. If symptoms persist, worsen, or occur away from phone use, seek advice from an optometrist or other qualified clinician. A phone’s dimming specification cannot determine the cause of an individual symptom.
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