Jessie Taylor
A foot-candle is a unit of measurement for light that reaches a surface area. It is used to determine the quantity of light that falls on a particular surface, as opposed to the amount of light that a source emits. Foot-candles are used in the US by architects, lighting specialists, and horticulturalists to calculate adequate lighting levels for various purposes. For example, foot-candles are used to measure lighting in workspaces, stores, and outdoor spaces.
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What You'll Learn
Foot-candles are a unit of illuminance
The foot-candle is a useful tool for businesses and organisations, as it helps them understand the lighting experience of customers and staff in their buildings. For example, hallways and lobbies require lower foot-candle readings to create a pleasant atmosphere, while work areas need higher readings to ensure sufficient lighting for tasks.
In the US, foot-candles are also used in museums and galleries to preserve light-sensitive objects, and in cinematography to set up the correct lighting ratios. Horticulturalists use foot-candles to determine the optimum light intensity for various plants, as light is a primary factor in photosynthesis.
While the term "foot-candle" may sound old-fashioned, it is still a widely used unit of measurement. The equivalent metric unit is the lux, which defines the area being lit as one square metre, rather than one square foot.
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They measure light as perceived by the human eye
Foot-candles are a unit of measurement used to determine the amount of light that reaches a surface area. They are a way to measure light as perceived by the human eye, or "photometry". This is different from "radiometry", which measures all forms of radiant energy, including light, in absolute terms.
The term "foot-candle" dates back to when beeswax candles were the primary source of lighting. It refers to the illumination produced by a source of one candle at a distance of one foot, which is equal to one lumen per square foot or approximately 10.764 lux. While the amount of visible light given off by a light source is measured in lumens, the number of lumens produced can vary drastically from the number of lumens that reach a surface, depending on factors such as shades or obstructions. Foot-candles tell us how bright a light source is perceived to be in a given space.
Foot-candles are commonly used by lighting design specialists and project managers to measure and quantify light levels in commercial or industrial spaces. They are also used by architects to calculate adequate lighting levels in workplaces, stores, and outdoor spaces. For example, foot-candles are used to determine lighting for athletic fields, ensuring that there is sufficient light for safe use.
Foot-candles are also important in the museum and gallery fields, where lighting levels must be carefully controlled to conserve light-sensitive objects such as prints, photographs, and paintings. Horticulturists use foot-candles to discuss and measure the optimum light intensity for various plants, as light is a primary factor in photosynthesis. In cinematography, incident light meters are used to measure foot-candles, allowing cinematographers to set up proper lighting-contrast ratios when filming.
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Foot-candles are used in horticulture to measure light for plants
Foot-candles are a unit of illuminance or illumination, equivalent to the illumination produced by a source of one candle at a distance of one foot. In other words, it measures the intensity of light falling on a surface. This is different from measuring the amount of light that leaves a light source (lumen output).
There is no clear consensus on what levels of light individual plants need, and foot-candle recommendations vary. However, some plants classified as ""indoor" plants are actually tropical understory plants, meaning they have adapted to the filtered light available on the jungle floor. Therefore, too much direct sun can burn these plants.
To measure foot-candles, a hand-held, digital light meter is often used. If the unit displays readings in foot-candles or lux, and is accurate to one foot-candle, it will be sufficient for houseplants. There are also many phone applications that help your device measure light levels, such as Light Meter for iPhones.
It is important to note that foot-candles are an imprecise form of measurement, and that the human eye automatically compensates for brightness, making judging light levels difficult. However, foot-candles give a good idea of how much light a plant is getting and can help determine the amount of light required for various environments.
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They're used in cinematography to measure lighting for filming
Foot-candles are a unit of measurement for light intensity, or illuminance, and are used in cinematography to measure lighting for filming. Cinematographers use light meters to measure the number of foot-candles and calculate the intensity of motion picture lights, allowing them to set up the proper lighting and contrast ratios when filming.
Foot-candles are defined as one lumen per square foot, and this unit is commonly used in the United States and other countries that follow US customary units of measurement. In simple terms, one foot-candle is the amount of light produced by a standard candle placed one foot away from the subject. This measurement focuses on the amount of light reaching a surface area, rather than the light emitted from the source.
In cinematography, foot-candles are used to determine the lighting requirements for different scenes and ensure consistent lighting across shots. Cinematographers may use light meters that provide readings in foot-candles, or they may memorise conversions, such as 100fc being equivalent to f/2.8 at ISO 100. This allows them to quickly adjust lighting setups and camera settings accordingly.
Additionally, foot-candles are crucial in the film industry for preserving light-sensitive objects. Museums and galleries use foot-candle measurements to ensure that lighting levels are carefully controlled to prevent damage to sensitive artifacts, prints, photographs, and paintings. Similarly, in cinematography, proper lighting techniques based on foot-candle measurements can help protect light-sensitive materials used in set design or costume fabrication.
While foot-candles are widely used in the US, other parts of the world, especially Europe, use the SI-derived unit "lux" for illuminance measurements. One foot-candle is approximately equal to 10.764 lux, and in many practical applications, it is considered sufficient to treat one foot-candle as approximately ten lux. Cinematographers and lighting professionals may need to be familiar with both units, depending on the production's location and equipment specifications.
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Foot-candles are used to measure lighting in museums and galleries
A foot-candle is a unit of measurement for light intensity. It is defined as one lumen of light per square foot. In other words, it measures the amount of light that reaches a surface area of one square foot. This is different from simply measuring the amount of light that a source emits.
Museums also require specific light levels to create the right ambiance. Hallways and lobbies, for example, need lower light levels than work areas. Foot-candle measurements are used to ensure that the desired amount of light is reaching the intended areas.
In the motion picture cinematography field, incident light meters are used to measure the number of foot-candles present. This allows cinematographers to set up the proper lighting-contrast ratios when filming.
Foot-candles are a common unit of measurement in the US, where they are used by architects to calculate adequate lighting levels. In other parts of the world, such as Europe, the SI-derived unit "lux" is used instead. One foot-candle is equal to approximately 10.764 lux.
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Frequently asked questions
A foot-candle is a unit of illuminance or illumination, equivalent to the illumination produced by a source of one candle at a distance of one foot. It measures the amount of light that reaches a surface area.
Foot-candles are commonly used in the US by architects, lighting specialists, and horticulturalists to calculate adequate lighting levels. For example, a foot-candle reading might be taken to measure the amount of light on the ground surface beneath a parking lot light.
One foot-candle is equal to approximately 10.764 lux. Lux defines the area being lit as a one-meter square, while a foot-candle defines it as a one-foot square.
