In which unit is illuminance measured?

In which unit is illuminance measured?

• A. Footcandle (fc)
• B. Lumen (lm)
• C. Lux (lx)
• D. Watt per square meter (W/m²)

Answer: (C)

Illuminance is a measure of how much light is received on a surface and is defined as the luminous flux per unit area. The correct unit for measuring illuminance is lux (lx), which quantifies how much light (in lumens) is spread over a given area (in square meters). One lux is equivalent to one lumen per square meter, making it a direct measure of light intensity on a surface area. This makes lux particularly suitable for applications in lighting design, architecture, and other fields where understanding how light interacts with surfaces is crucial. While footcandle (fc) is also used to measure illuminance, particularly in the United States, it is not the standard international unit, which is lux. Lumen measures the total amount of visible light emitted by a source, and watts per square meter relates to power density rather than illuminance. Hence, lux is the most appropriate unit to describe illuminance.

Illuminance is a measure of how much light is received on a surface and is defined as the luminous flux per unit area. The correct unit for measuring illuminance is lux (lx), which quantifies how much light (in lumens) is spread over a given area (in square meters).

One lux is equivalent to one lumen per square meter, making it a direct measure of light intensity on a surface area. This makes lux particularly suitable for applications in lighting design, architecture, and other fields where understanding how light interacts with surfaces is crucial.

While footcandle (fc) is also used to measure illuminance, particularly in the United States, it is not the standard international unit, which is lux. Lumen measures the total amount of visible light emitted by a source, and watts per square meter relates to power density rather than illuminance. Hence, lux is the most appropriate unit to describe illuminance.