📱 "Camera shows horizontal lines but eyes don't see flicker" (PWM frequency)
What's happening: PWM (Pulse Width Modulation) dimming rapidly turns backlight on/off at 120-480Hz to control brightness. Camera shutter speed (1/60s, 1/120s) captures backlight in different ON/OFF states creating horizontal bands in photos/video. Human eyes don't consciously see >100Hz flicker but subconscious processing may cause eye strain, headaches, or discomfort after prolonged use. Worse at low brightness (0-30%).
PWM frequency ranges: Budget monitors (AOC, ViewSonic): 120-250Hz PWM = visible flicker to sensitive users. Mid-range (Dell, ASUS): 250-500Hz = less noticeable. High-end/flicker-free (BenQ, EIZO): DC dimming or >1000Hz PWM = imperceptible. Test with camera: Record at 60fps - more horizontal bands = lower PWM frequency. Phones use similar dimming: iPhone OLED 240Hz, Samsung Galaxy 240-480Hz (varies by model).
✅ Solution: If sensitive to PWM: Use brightness 70-100% (many monitors switch to DC dimming above 70%). Enable "Flicker-Free" mode if available (ASUS VG279Q, BenQ EW2780Q). Use external lighting instead of lowering monitor brightness. Upgrade to DC dimming monitor (check reviews - TFTCentral tests PWM). OLED monitors (LG 27GR95QE) use per-pixel dimming with high-frequency PWM (3840Hz) - less noticeable. Or choose W-LED edge-lit monitors with DC dimming (some Dell UltraSharp models).
💡 "Flicker-free at 100% brightness but flickers at 30-50%" (Hybrid dimming)
What's happening: Hybrid dimming system: DC (Direct Current) dimming at high brightness (70-100%), PWM dimming at low brightness (0-70%). DC dimming adjusts LED voltage directly - no flicker but can cause color shift at low brightness. PWM maintains color accuracy at low brightness but introduces flicker. Transition point (70% typical) varies by manufacturer. Some monitors advertise "flicker-free" but only above 50% brightness.
Why manufacturers use hybrid: Pure DC dimming: Color temperature shifts 500-1000K from 100% → 20% brightness (whites turn yellow). Pure PWM: Flicker risk but stable colors. Hybrid compromise: Best of both but confusing for users. ASUS, BenQ, LG use hybrid. Budget monitors (Acer, MSI gaming): PWM across full range (0-100%). Professional monitors (EIZO ColorEdge): True DC dimming with LUT calibration compensating color shift - no PWM at any brightness.
✅ Solution: Check monitor reviews (TFTCentral, RTINGS) for PWM testing at multiple brightness levels. If hybrid PWM starts < 70%: Stay above that brightness, use room lighting to compensate. Adjust monitor OSD: Some allow choosing "DC Dimming" vs "PWM Dimming" mode. For dark room usage requiring low brightness: Upgrade to true DC dimming monitor or high-frequency PWM (>1000Hz). OLED with high PWM frequency (3840Hz on LG OLED) acceptable for most users.
📸 "Camera test shows banding - is this harmful?" (PWM sensitivity varies)
What's happening: Individual PWM sensitivity varies widely. Some users: No issues with 120Hz PWM for years. Others: Immediate eye strain, migraine, or nausea from 250Hz PWM. Risk factors: Photosensitive epilepsy (rare, <1% population), migraine sufferers (15% population more PWM-sensitive), people with astigmatism or eye focusing issues. Long-term health effects unclear - no conclusive studies on sub-conscious flicker damage.
Symptoms of PWM sensitivity: Immediate (<1 hour): Eye strain, dry eyes, difficulty focusing, headache starting behind eyes. Delayed (2-4 hours): General headache, neck tension, nausea, "heavy eyes" feeling. Chronic: Insomnia if using monitor before sleep (melatonin suppression), general eye fatigue. Not everyone affected - if you don't feel symptoms after 4+ hours use, likely not sensitive. Camera test confirms PWM presence but doesn't predict your sensitivity.
✅ Solution: Self-test: Use monitor at 50% brightness (where PWM active) for 2-3 hours. Monitor symptoms. No issues = PWM doesn't affect you - camera showing bands is irrelevant. If symptoms develop: Increase brightness, add ambient lighting, take breaks (20-20-20 rule: every 20 mins, look 20 feet away for 20 seconds). Long-term sensitive: Invest in flicker-free monitor (BenQ EW2780Q, Dell P2723DE with DC dimming). Blue light filters help with sleep but don't eliminate PWM flicker.
😣 "Eye strain even on flicker-free monitor" (Other causes beyond PWM)
What's happening: "Flicker-free" only addresses PWM backlight - many other eye strain causes. Temporal dithering (FRC on 6-bit panels): 60-120Hz color flickering in gradients. VRR flicker: G-Sync/FreeSync changing refresh rate 40-144Hz causes luminance changes. Poor ergonomics: Monitor too bright (300+ nits in dark room strains eyes), too close (<20" from 27" monitor), wrong height (top of screen should be eye level).
Other technical causes: Low refresh rate (60Hz has visible sample-and-hold "shimmer" vs 120Hz+ smoother). Overdrive overshoot causing inverse ghosting (bright halos strain eyes tracking motion). Blue light exposure (450-480nm wavelength suppresses melatonin, harder eye focus). Poor pixel density (24" 1080p = 92 PPI shows individual pixels causing eye to constantly refocus). Ambient lighting too dim (high contrast between screen and room) or too bright (glare/reflections).
✅ Solution: Multi-factor approach: (1) Brightness: 120-150 cd/m² in office, 80-100 cd/m² in dark room - use lux meter or colorimeter. (2) Distance: Arm's length minimum (20-30" from 24-27" monitor). (3) Ergonomics: Top of screen at eye level, slight downward viewing angle (10-20°). (4) Lighting: Bias lighting behind monitor (6500K LED strip), no direct glare on screen. (5) Refresh rate: 120Hz+ reduces strain vs 60Hz. (6) Breaks: 20-20-20 rule. (7) Eye exam: Rule out vision problems (astigmatism, focusing issues).
🎮 "Screen brightness pulses during gaming" (VRR luminance changes)
What's happening: Variable Refresh Rate (VRR) changing monitor refresh dynamically (40-144Hz) causes perceived brightness fluctuations. LCD response time optimized for fixed refresh - at 60Hz pixels transition differently than 120Hz causing luminance variance. Worse on VA panels (slow pixel response 8-15ms) than IPS (4-6ms). G-Sync Compatible monitors (non-module) worse than hardware G-Sync (NVIDIA scaler compensates). FPS drops 144 → 60 Hz = visible "pulse".
Overdrive and VRR interaction: Fixed overdrive tuned for 144Hz looks wrong at 60Hz - too aggressive (inverse ghosting) or too weak (smearing). Variable overdrive (G-Sync module monitors) adjusts per refresh rate but can cause visible transitions. Some monitors (Samsung Odyssey G7, Gigabyte M27Q) have severe VRR flicker bugs - firmware issue. ELMB/ULMB strobing incompatible with VRR - must choose one. Frame rate consistency matters: Stable 100-120 FPS better than wildly varying 40-144 FPS.
✅ Solution: Update monitor firmware (VRR optimizations). Set VRR range narrower: NVIDIA Control Panel → Manage 3D Settings → Max Frame Rate → 138 FPS (for 144Hz monitor) prevents low-Hz flicker. In-game: Cap FPS to stable value (100/120) instead of unlocked. OSD: Lower overdrive to "Normal" (reduces VRR artifacts). For severe flicker: Disable VRR, use fixed 120/144Hz + V-Sync (trades tearing for stability). Or upgrade to G-Sync Ultimate monitor with variable overdrive (ASUS PG27AQN, $899) or OLED with instant response (no overdrive needed).