foot-lambert
Noun: A unit of measurement for luminance (the intensity of light emitted or reflected from a surface). One foot-lambert is defined as a luminance of one lumen per square foot. It is a non-SI unit historically used in photometry, particularly in contexts related to screen brightness and reflected light.
The term is used in technical and historical contexts to specify the brightness of a surface. * The old projector screen had a luminance of approximately 30 foot-lamberts. * This measurement, expressed in foot-lamberts, helps calibrate the display's perceived brightness.
- The foot-lambert is directly related to the apostilb, another non-SI luminance unit. One foot-lambert is approximately equal to 3.426 apostilbs.
- In modern scientific contexts, the SI unit for luminance, the candela per square meter (cd/m² or nit), has largely superseded the foot-lambert.
- Lambert (L): A related, larger unit of luminance. One lambert is equal to 1/π candela per square centimeter. The foot-lambert is 1/π candela per square foot.
- Luminance: The physical quantity being measured, describing the luminous intensity per unit area of light traveling in a given direction.
- Nit (cd/m²): The modern SI unit for luminance, now more commonly used than the foot-lambert.
- Apostilb (asb): A closely related non-SI luminance unit (1 fL ≈ 3.426 asb).
This word has a single, specific technical meaning as a unit of measurement. It is considered an archaic or legacy unit in most contemporary technical fields.
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a former luminance unit equal to one lumen per square foot
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