What is the unit that describes the illumination produced by one candle at a distance of 1 foot?

What is the unit that describes the illumination produced by one candle at a distance of 1 foot?

• A. Foot Candle
• B. Lumen
• C. Lux
• D. Candela

Answer: (A)

Illuminance on a surface is quantified by how much light lands on that surface from a source at a specific distance. The unit foot-candle is defined exactly this way: it measures the illumination produced on a surface by a light source of one candela at a distance of one foot. In practical terms, one foot-candle is equivalent to one lumen per square foot. So when a candle sits one foot away from a surface, the surface receives about one foot-candle of illumination. Lumen describes the total amount of light emitted by the source, not how much lands on a surface. Candela refers to the brightness of the source in a particular direction (luminous intensity), not the illuminated level on a surface. Lux is the metric counterpart of foot-candle (one lux equals about 0.0929 foot-candle), measuring illuminance per square meter. Since the scenario specifies illumination at a one-foot distance from a single candle, foot-candle is the exact term for that measurement.

Illuminance on a surface is quantified by how much light lands on that surface from a source at a specific distance. The unit foot-candle is defined exactly this way: it measures the illumination produced on a surface by a light source of one candela at a distance of one foot. In practical terms, one foot-candle is equivalent to one lumen per square foot. So when a candle sits one foot away from a surface, the surface receives about one foot-candle of illumination.

Lumen describes the total amount of light emitted by the source, not how much lands on a surface. Candela refers to the brightness of the source in a particular direction (luminous intensity), not the illuminated level on a surface. Lux is the metric counterpart of foot-candle (one lux equals about 0.0929 foot-candle), measuring illuminance per square meter. Since the scenario specifies illumination at a one-foot distance from a single candle, foot-candle is the exact term for that measurement.