Maddie James
Foot-candles and lux are both units of measurement used to determine light intensity. A foot-candle is a non-SI unit of illuminance or light intensity commonly used in the United States, whereas lux is the corresponding SI-derived unit used in most other parts of the world. One foot-candle is approximately equal to 10.76 lux. This means that to convert foot-candles to lux, you divide by 10.76, and to convert lux to foot-candles, you multiply by 10.76.
Foot-candles vs Lux
| Characteristics | Values |
|---|---|
| Definition | Foot-candles are a non-SI unit of illuminance or light intensity. Lux is the corresponding SI-derived unit. |
| Unit | Foot-candles are measured in lumens per square foot. Lux is measured in lumens per square meter. |
| Conversion | 1 foot-candle = approximately 10.76 lux. 1 lux = approximately 0.0929 foot-candles. |
| Usage | Foot-candles are commonly used in the US and other places that follow US customary units. Lux is used in most other parts of the world, including Europe. |
| Application | Foot-candles are used in lighting layouts, electrical construction, and to ensure that specific areas receive the required light levels. Lux is used to determine light intensity and appropriate lighting levels in commercial, industrial, and sports spaces. |
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What You'll Learn
One foot-candle equals 10.76 lux
A foot-candle is a unit of illuminance or light intensity, defined as one lumen per square foot. This unit is commonly used in lighting layouts in parts of the world where United States customary units are used, such as the US and the UK. The foot-candle is defined as the illuminance of the inside surface of a one-foot-radius sphere with a point source of one candela at its centre. Alternatively, it can be defined as the illuminance of one lumen on a one-square-foot surface with a uniform distribution.
In many other parts of the world, the SI-derived unit "lux" is used. Lux is essentially the same as foot-candles, but it defines the area being lit as a one-metre square, rather than a one-foot square. So, one lux is equal to 0.092903 foot-candles. A lumen is the amount of light given off by a light source, where a foot candle is the measure of lumens per square foot.
Given the relation between candela and lumen, the two definitions of a foot-candle are identical, with the second one potentially being easier to relate to in some everyday situations. One foot-candle is equal to approximately 10.76 lux. In many practical applications, as when measuring room illumination, it is often not needed to measure illuminance more accurately than ±10%. In these situations, it is sufficient to think of one foot-candle as about ten lux.
Light intensity is the primary factor in the photosynthesis of plants, so US horticulturalists often measure and discuss optimum intensity for various plants in foot-candles. Full, unobstructed sunlight has an intensity of up to 930 fc. An overcast day will produce an intensity of around 100 fc. The intensity of light near a window can range from 100 to 460 fc, depending on the orientation of the window, time of year and latitude.
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Lux is the metric measurement for light
Light intensity is a crucial factor in various contexts, from horticulture to commercial lighting. The measurement of light intensity is necessary to ensure optimal lighting conditions for specific tasks, conserve artwork, and provide adequate illumination for different spaces. While the foot-candle is a unit of illuminance or light intensity, it is an imperial measurement primarily used in the United States. Lux, on the other hand, is the metric measurement for light.
A foot-candle is defined as one lumen per square foot. This unit is especially relevant in the US lighting industry, where architects and lighting professionals use it to calculate appropriate lighting levels. It is also commonly employed in museums and galleries, where precise control of lighting is essential for preserving light-sensitive artworks. In the field of horticulture, US horticulturalists rely on foot-candles to determine the optimum light intensity for different plants.
However, in most parts of the world, the SI-derived unit, lux, is the standard for measuring light. Lux is defined as one lumen per square meter, making it a metric measurement. This unit is commonly used in places that follow the International System of Units (SI), such as Europe. Lux is advantageous because it defines the area being illuminated as a one-meter square, providing a larger reference area than the foot-candle.
The conversion factor between foot-candles and lux is approximately 10.76. Thus, one foot-candle is equivalent to approximately 10.76 lux, and to convert lux to foot-candles, you divide by this factor. For example, 15 foot-candles would be approximately 161.46 lux (15 x 10.76).
Understanding the relationship between foot-candles and lux is essential for ensuring proper lighting in various contexts. Lux, as the metric measurement, offers a standardized way to quantify light intensity, making it a valuable tool for professionals in fields ranging from architecture to horticulture.
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Foot-candles are a unit of illuminance
Nearly all of the world uses the corresponding SI-derived unit, lux, defined as one lumen per square meter. Lux is the same as foot-candles but measures a one-metre-square area, rather than a one-foot-square area. One foot-candle is equal to approximately 10.76 lux, or 10 lux when rounded to the nearest whole number. In many practical applications, such as when measuring room illumination, it is sufficient to think of one foot-candle as about ten lux.
To convert lux to foot-candles, divide your lux reading by 10.76. For example, 15 lux is equal to approximately 1.4 lux, or 1.39 lux when rounded to two decimal places.
Light meters are available from many manufacturers at various price points. Most light meters will output their readings in foot-candles or lux.
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Lux is a derived SI unit
The lux (lx) is a derived SI unit of illuminance, or luminous flux per unit area. It is equal to one lumen per square meter. In photometry, lux is used as a measure of the irradiance, as perceived by the spectrally unequal responding human eye, of light that hits or passes through a surface. The unit is analogous to the radiometric unit watt per square meter, but with the power at each wavelength weighted according to the luminosity function, a model of human visual brightness perception standardized by the CIE and ISO. The word "lux" is derived from the Latin word for "light".
The foot-candle is a non-SI unit of illuminance or light intensity. It is defined as one lumen per square foot and is commonly used in lighting layouts in parts of the world where United States customary units are used, mainly the US. One foot-candle is equal to approximately 10.76 lux. In many practical applications, such as measuring room illumination, it is often sufficient to consider one foot-candle as about ten lux.
The lumen is a significant entity in the measurement of light as it quantifies the total amount of visible light emitted by a given source. All other measurements are based on the lumen. The lumen measurement originated from the basic concept of foot-candles. A foot-candle equals one lumen per square foot, and using the metric system, a lumen is measured by a square meter or a lux. Thus, a foot-candle is equivalent to approximately 10 lux.
As with other named SI units, SI prefixes can be used with lux. For example, 1 kilolux (klx) is 1000 lx. The illuminance provided by a light source on a surface perpendicular to the direction of the source is a measure of the strength of that source as perceived from that location. For instance, a star of apparent magnitude 0 provides 2.08 microlux (mlx) at the Earth's surface. A barely perceptible magnitude 6 star provides 8 nanolux (nlx).
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Foot-candles are used in the US
Foot-candles and lux are both units of illuminance or light intensity. One foot-candle is approximately equal to 10.76 lux, or 10 lux when rounded to the nearest 10%.
Foot-candles are also used in the US in the museum and gallery fields, where lighting levels must be carefully controlled to conserve light-sensitive objects such as prints, photographs, and paintings. Cinematographers in the motion picture cinematography field use foot-candles to set up proper lighting-contrast ratios when filming.
US horticulturalists also use foot-candles to discuss and measure the optimum light intensity for various plants, as light intensity is the primary factor in photosynthesis.
In summary, foot-candles are used in the US in various industries, including lighting, museums and galleries, cinematography, and horticulture, to measure and control light intensity and ensure adequate lighting levels for specific purposes.
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Frequently asked questions
A foot-candle is a unit of illuminance or light intensity. It is defined as one lumen per square foot. Foot-candles are used in lighting layouts in places that follow United States customary units of measurement.
Lux is the SI-derived unit of illuminance or light intensity. It is defined as one lumen per square meter. Lux is used in places that follow the metric system, such as Europe.
One foot-candle is equal to approximately 10.76 lux. To convert from lux to foot-candles, divide your lux figure by 10.76.
