How the Measurement Works

Where supported, the tool first uses the device Ambient Light Sensor, which reports illuminance directly in lux. On most mobile browsers this sensor is not exposed to websites, so the tool automatically switches to camera-based photometric estimation.

Camera mode analyses the central image area over multiple frames and converts RGB values to linear-light luminance. If the browser exposes camera exposure time and ISO, these are used to compensate for automatic camera exposure and improve consistency across different light levels.

Camera exposure, lens transmission, aperture, image processing and sensor response vary between devices. Calibration against a suitable reference lux meter substantially improves camera-based measurements for the same device and camera.

Browser-based camera measurements are estimates and are not a replacement for a calibrated photometric instrument where regulatory, occupational, laboratory or compliance-grade measurements are required.