When considering a lighting upgrade, which element focuses on how light levels are measured over a given area?

The focus on how light levels are measured over a given area is encapsulated by the concept of illumination level. This term refers specifically to the amount of light that is cast onto a surface and is typically measured in units such as foot-candles or lux. It considers both the intensity of the light source and how it disperses across the area in question, making it a critical factor in assessing the effectiveness of lighting upgrades.

While foot-candles is a unit that quantifies illumination levels, the term "illumination level" itself encompasses the broader context of the measurements and their implications for lighting design and effectiveness. Efficacy relates to how well a light source converts electrical energy into light but does not directly convey the light's distribution over an area. Distribution refers to how light is spread out in a space, which is linked but not specifically focused on measuring the levels of illumination themselves. Therefore, "illumination level" is the most appropriate choice when discussing the measurement of light intensity across a given area.