Lux (lx) is the SI unit of illuminance: luminous flux received by a surface per unit area. One lux equals one lumen per square meter. Lux depends on the light pattern, distance, aiming, mounting position, and the number of lights, so lumens alone do not determine the lux at a work area. Illuminance normally decreases as distance from a source increases, although the exact result depends on the lamp’s distribution and geometry. Lux measurements are useful for checking whether a lighting installation provides sufficient light at defined points. They should be made on a stated plane with consistent distance, orientation, and ambient conditions.