footcandle
Definition
Noun: A footcandle is a unit of measurement for illuminance, or the amount of light that falls on a surface. Specifically, one footcandle is defined as the illuminance on a surface that is everywhere one foot away from a uniform point light source with an intensity of one candela.
Usage
The term is used in technical contexts, particularly in lighting design, architecture, photography, and engineering, to quantify light levels. It describes how much light is actually present on a surface area.
Examples
- The building code requires a minimum of 30 footcandles of illumination on office work surfaces.
- To read comfortably, a light level of about 10 to 20 footcandles is recommended.
- The photographer measured the light on the subject's face and found it was 50 footcandles.
Advanced Usage
- Historical Context: The footcandle was a common unit in countries using the imperial system (like the United States) but has largely been superseded by the lux, the SI unit for illuminance (1 footcandle ≈ 10.764 lux).
- Technical Calculation: It is a direct measure of luminous flux per unit area. One footcandle equals one lumen per square foot.
Variants and Related Words
- Illuminance (n): The general concept of the total luminous flux incident on a surface per unit area. Footcandle is a unit of illuminance.
- Lux (n): The SI unit of illuminance, equal to one lumen per square meter.
- Candela (n): The SI unit of luminous intensity, which is part of the definition of a footcandle.
- Lumen (n): A unit of measurement for the total quantity of visible light emitted by a source.
Synonyms
- Light level (general term)
- Illuminance (the measurable quantity for which footcandle is a unit)
Related Phrases
- Footcandle meter: (Also called a light meter) An instrument used to measure illuminance in footcandles.
- The engineer used a footcandle meter to check if the factory lighting met the safety standards.
Noun
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a unit of illuminance on a surface that is everywhere 1 foot from a point source of 1 candle
