Foot-candle

Foot-candle (fc, lm/ft²) is a non-SI unit of Illuminance or Light intensity. It measures the amount of Luminous flux per square foot. In the metric system, the foot-candle is replaced by the lux, with one foot-candle being equivalent to approximately 10.764 lux. The foot-candle is used primarily in the United States, whereas most other countries use lux for measuring illuminance.

Definition

A foot-candle is defined as one lumen per square foot. This unit of measure is useful in determining adequate lighting levels for various environments. For example, an office space may require a lighting level of 30 to 50 foot-candles for optimal visibility and comfort.

Applications

Foot-candles are commonly used in the fields of Cinematography, Photography, Architecture, and Interior design to ensure that adequate lighting is achieved. In Horticulture, foot-candles are used to measure the intensity of light reaching plants, which is critical for photosynthesis and the overall health of the plant.

Measurement

The measurement of foot-candles is typically done with a Light meter that can be set to display readings in either foot-candles or lux. Proper measurement involves taking readings at various locations within a space to ensure even distribution of light.

Standards and Recommendations

Various organizations, such as the Illuminating Engineering Society (IES), provide guidelines for the minimum foot-candle levels required for different settings. For instance, museum exhibits may require lighting of at least 5 to 50 foot-candles depending on the sensitivity of the items on display, while mechanical workshops may need 30 to 75 foot-candles for safe and efficient operation.

Conversion to Lux

To convert foot-candles to lux, multiply the number of foot-candles by 10.764. This conversion is necessary when working with international standards or equipment calibrated in metric units.

See Also

• Lumen
• Lux
• Illuminance
• Light meter