CISSP Practice Exam 2026 – Complete Prep Guide

The definition of Lux, a unit used to measure illuminance, is indeed one lumen per square meter. This measurement quantifies the amount of light that is received on a surface area. The lux is specifically designed to provide an understanding of how well a certain area is illuminated, making it vital in various fields such as photography, architecture, and safety assessments.

By setting the definition as one lumen per square meter, Lux takes into account both the intensity of the light source (measured in lumens) and how that light spreads over a particular area. This characteristic allows for a practical assessment of lighting conditions in terms of human perception and comfort, thus highlighting its importance in establishing adequate and effective lighting in both indoor and outdoor environments.

The other options refer to different physical quantities: a foot-candle is an illuminance measurement based on a different standard, watts pertain to power, while joules describe energy; none are related to the specific definition of Lux as clearly as lumens per square meter.