Sky Ember Journal
Why your MacBook might give you headaches at low brightness
If your eyes ache or your head throbs after evenings at a dim screen, and the symptoms ease at full brightness or on paper, the culprit may be something you can't consciously see: PWM flicker.
What PWM is
Most displays don't dim by lowering their light's intensity. They dim by pulsing: switching the backlight (or each OLED pixel) fully on and off hundreds or thousands of times per second, spending more time "off" the dimmer you go. This is pulse-width modulation. At 50% brightness the panel may be dark half of every cycle; your visual system averages the pulses into "dimmer," but in some people the flicker is still processed, showing up as strain, fatigue, or headache.
Sensitivity varies enormously. Many people never notice PWM at any frequency. Others react to anything below a few kilohertz. If low-brightness screens bother you while bright ones don't, you're in the second group.
Test your own display in 30 seconds
Set your screen to about 30% brightness, open your phone's camera, and point it at the display while watching the phone's preview. Rolling dark bands across the preview mean your panel is pulsing at a frequency the camera can catch. Now set the screen to 100%. On most panels the bands vanish, because at full brightness there's nothing to pulse.
What actually helps
- Keep the backlight where it doesn't pulse. Typically that means at or near maximum, or above the panel's PWM threshold.
- Dim in software instead. Remapping every pixel darker in the display's gamma table lowers the light reaching your eyes without touching the backlight. Nothing pulses, ever. This is the "brightness without PWM" approach, and it can also dim far below the hardware minimum for dark rooms.
- Warm the screen in the evening. Less blue-green output is simply less of the light most implicated in evening strain.
Sky Ember is built around exactly this combination: flicker-free soft dimming with shadow compensation (so dimmed blacks stay black instead of turning milky), sun-timed warmth, and a true red mode for full darkness.