lux second

Total exposure of the film or sensor, the product of focal-plane illuminance times exposure time, is measured in lux seconds.

Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.

ISO speed ratings of a digital camera are based on the properties of the sensor and the image processing done in the camera, and are expressed in terms of the luminous exposure H (in lux seconds) arriving at the sensor.