Point a second device’s camera at a plain screen area. This tool describes bands in the camera image. It cannot measure physical PWM frequency or modulation depth, identify the cause of bands, or certify safety. Processing stays in your browser.
Capture the same plain screen area with hardware dimming and with software dimming. Keep the framing and camera settings fixed where possible. Changes describe these camera images; automatic exposure and display content can change the result independently of the physical waveform.
Turn Tap Zap OFF. Choose a comfortable hardware brightness. Aim at a plain white area, hold steady, and capture. Record the setting.
If comfortable, set hardware brightness to 100%, turn Tap Zap ON, and dim the picture in software. Keep the same white area, framing, and exposure. Maximum hardware brightness does not guarantee absence of PWM.
Many cameras use a rolling shutter, exposing different rows at different times. Temporal light variation can appear as bands. Image content, ambient lighting, sensor processing, and aliasing can also affect the pattern.
Row timing and exposure differ across cameras and modes. The browser does not provide a calibrated row-readout time. A camera can miss temporal variation; an image without bands is inconclusive.
We draw each frame to a canvas, read the pixels, and collapse each row to a single brightness value. The result is a 1D signal — brightness versus row — shown in the waveform above.
An FFT summarizes repeating brightness patterns across image rows. We report cycles across the sampled frame and a relative image-band amplitude. Neither number measures the time-domain optical waveform.
No result here establishes flicker-free light, a safe display, or a health outcome.
The dominant repeating row pattern, in bands per sampled frame. This is a spatial image measure, not hertz. Static stripes and camera/display interference can produce the same pattern as temporal variation.
The dominant row-pattern amplitude relative to mean camera-image brightness, expressed as a percentage. Exposure, clipping, gamma processing, focus, and content affect it. It is not optical modulation depth.
Tap Zap adjusts screen warmth and software brightness. PWM-Safe holds supported hardware brightness at 100%, which may reduce brightness-control PWM on some displays. Optical behavior is display-specific; the mode is not a safety certification.