Most LED bulbs and fluorescent tubes flicker at 50 or 100 Hz — too fast to see,
but your phone's camera captures it frame by frame. Sustained exposure to invisible
flicker causes headaches, eye strain, and migraines in sensitive people.
Point the camera at any light source and see what your eyes are missing.
cheap LED bulbs can flicker up to 120 times per second.
Offices lit with LED panels commonly run at 100% flicker depth — the light actually
goes completely off between pulses. EEG studies show this disrupts alpha waves in the
brain even when subjects report no discomfort. Some people are more sensitive than others.
Your phone already knows. You just never looked.
point at a light source
—
Hz · flicker frequency
waiting
—freq Hz
—depth %
—camera fps
verdict
Point the camera at any light source — lamp, screen, ceiling light — to begin analysis.
LED and fluorescent lights typically show 50Hz or 100Hz flicker. Incandescent and sunlight show none.
▶ why does flicker matter?
The human visual system can detect flicker up to about 60 Hz consciously. Above that,
flicker is invisible but not necessarily harmless. The IEEE has guidelines (IEEE 1789) that
recommend flicker depth below 8% at 100 Hz to avoid health effects.
The camera captures frames at 30 or 60 fps. To detect 100 Hz flicker, we need a camera
that can sample faster than 200 Hz (Nyquist). Most phone cameras have a high-speed mode
(120/240 fps) but the browser API typically exposes 30 or 60 fps. At 60 fps we can reliably
detect 50Hz and 60Hz (one alias each). Higher frequencies may alias — we report them with a note.