Which light measurement indicates intensity of illumination on a surface?

Footcandles are the measure that indicates the intensity of illumination on a surface. This unit quantifies how much light is illuminating a specific area, specifically a surface that is one square foot in size, when one lumen of light is uniformly distributed across that area. It is a practical and common measurement used in lighting design to assess how well lit an area is, which is critical for various applications such as workplace settings, retail environments, and residential spaces.

Understanding this measurement helps lighting professionals ensure adequate lighting levels that support tasks and enhance visibility without causing glare or discomfort. Other measurements like lumens represent the total amount of light produced by a source, candelas refer to luminous intensity in a particular direction, and lux is the metric equivalent of footcandles, measuring the illumination on a surface in square meters. However, footcandles specifically pertain to intensity per area, making them the appropriate choice for this question.