What unit is used to measure luminance emitted or reflected from an area?

The correct choice is candelas per square meter or foot lamberts. These units are specifically designed to measure luminance, which refers to the quantity of light emitted or reflected from a surface in a given direction per unit area. Luminance is important in various fields, including industrial hygiene and lighting design, as it affects visibility and overall work environment conditions.

Candelas, which are a measure of luminous intensity, offer a precise way to quantify how much light is perceived from a surface. When this measurement is normalized to area (such as per square meter), it effectively provides a comprehensive understanding of how bright that surface appears from a particular viewpoint.

Other units, such as lux and foot candles, measure illuminance, which refers to the total amount of light hitting a surface area rather than the light being emitted or reflected from it. Watts per square meter measures power per unit area and is more about energy rather than how that energy manifests as visible light.

Therefore, candelas per square meter captures the concept of luminance accurately, providing a necessary specification for situations where seeing and assessing light levels is critical for health and safety.