In a lighting plan, what does an illuminance value expressed in foot-candles represent?

• A. The luminous flux incident on a surface per unit area (lumens per square foot)
• B. Total lumens emitted by a light source
• C. The luminous intensity in a given direction
• D. The power consumption of a lighting fixture

Answer: (A)

Illuminance is the amount of light that arrives on a surface. When expressed in foot-candles, it indicates lumens per square foot on that surface, i.e., how many lumens fall onto each square foot of area. This distinguishes it from total luminous flux (how many lumens the fixture emits overall), luminous intensity (how bright the light is in a specific direction), or electrical power (watts used by the fixture). So the foot-candle value directly represents lumens per square foot on the surface.