Point your camera at a light source. Get frequency, modulation depth, and a quick health verdict in seconds.
Tap Start, then aim at a light source for 2–3 seconds.
Many LED, fluorescent, and screen lights pulse rapidly. Even when you can't see it, low-frequency or deep-modulation flicker is linked to headaches, eye strain, and reduced focus.
Phone cameras capture each row of an image at slightly different moments (rolling shutter). A flickering light shows up as horizontal banding in a single frame.
FlickerTest reads the brightness of each row, finds the periodic pattern, and converts band spacing into frequency in Hz.
Frequency. 100 Hz or 120 Hz means standard mains-driven LED. Above 200 Hz usually indicates PWM dimming. Below 80 Hz is biologically problematic.
Modulation %. Peak-to-peak amplitude vs average brightness. IEEE 1789 considers under 8% safe at 100 Hz, under 25% acceptable.
Flicker Index. A more rigorous waveform metric. Below 0.1 is generally fine.
Hold the phone 20–50 cm from the light, fill most of the frame, and stay still for 2–3 seconds.
Test in a dim room with the target light as the dominant source — bright ambient light washes out banding.
For lab-grade measurements, use a calibrated photodiode and oscilloscope. This tool is for quick checks.