Jessie Taylor
Foot-candles and lumens are both units of measurement used to describe light intensity. Foot-candles are a non-SI unit of illuminance, defined as one lumen per square foot. This unit is commonly used in lighting layouts in the United States. Lumens, on the other hand, measure the quantity of light produced by a fixture. This means that one foot-candle is equal to one lumen per square foot. In other words, if you have a light source emitting one lumen of light, and it spreads out evenly over a one-square-foot area, you would have a light intensity of one foot-candle in that area.
| Characteristics | Values |
|---|---|
| Definition | A foot-candle is a non-SI unit of illuminance or light intensity. |
| In Layman's Terms | One foot candle equals 1 lumen per square foot. |
| Metric Equivalent | One foot-candle is equivalent to approximately 10.764 lux. |
| Usage | Foot-candles are a common unit of measurement used by architects to calculate adequate lighting levels. They are also used in the museum and gallery fields, sports lighting, and cinematography. |
| Practical Applications | In many practical applications, such as measuring room illumination, it is often sufficient to consider one foot-candle as about ten lux. |
| Compliance | Compliance with foot-candle and lighting standards is essential for safe and adequately lit workplaces. |
| Conversion | To convert lux to foot-candles, divide your lux reading by 10.76. |
| Examples | Indoor lighting for residences: 5-40 fc for general spaces, 70-90 fc for workspaces. |
| Full, unobstructed sunlight: up to 930 fc. |
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What You'll Learn
One foot candle equals 1 lumen per square foot
One foot-candle is equal to one lumen per square foot. This unit is used to measure light intensity, specifically the illuminance of one lumen on a one-square-foot surface. Foot-candles are a non-SI unit of measurement, primarily used in the United States, where United States customary units are standard. The SI-derived unit for measuring light intensity is lux, which is defined as one lumen per square meter.
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. This is equivalent to one lumen per square foot. In other words, a foot-candle measures the light that reaches a surface, while lumens measure the quantity of light produced by a fixture.
Foot-candles are important for measuring light intensity in various contexts, including commercial, industrial, and sports lighting. For example, in sports lighting, foot-candles ensure optimal visibility for players and spectators. In the motion picture cinematography field, incident light meters are used to measure the number of foot-candles present, allowing cinematographers to set up proper lighting-contrast ratios when filming.
In practical applications, such as measuring room illumination, it is often sufficient to consider one foot-candle as approximately ten lux. This conversion factor is based on the relationship between the two units: one foot-candle is equal to approximately 10.76 lux. Therefore, if you have a light meter that only reads in lux, you can divide your reading by 10.76 to convert it to foot-candles.
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Foot candles are the imperial measurement
Foot candles are a measure of the light that reaches a surface, while lumens measure the quantity of light produced by a fixture. In other words, a lumen is the amount of light given off by a light source, whereas a foot candle measures the light over a specific area. This is why foot candles are defined as the illuminance of the inside surface of a one-foot-radius sphere with a point source of one candela at its centre.
The foot candle is a non-SI unit, with the SI-derived equivalent being lux, which measures light over a one-metre square area. One foot candle is equal to approximately 10.76 lux, so conversion between the two units is a simple division or multiplication. Lux is the metric equivalent of the foot-candle and is used almost everywhere outside of the US.
In the US, foot candles are used to calculate lighting levels in a variety of settings. For example, the Illuminating Engineer Society (IES) recommends a foot-candle reading of 10 for a parking garage. If the lighted areas are reading 7 foot-candles, then more lumens are needed to brighten the space. In sports lighting, foot-candles are used to ensure optimal visibility for players and spectators.
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Lux is the metric measurement
A foot-candle is a unit of illuminance or light intensity. It 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. In other words, it is the illuminance of one lumen on a one-square-foot surface with a uniform distribution. One foot-candle is equal to one lumen per square foot. This unit is commonly used in lighting layouts in the United States.
Lux, on the other hand, is the metric measurement of illuminance. It is defined as one lumen per square metre. Nearly all of the world uses this SI-derived unit, whereas foot-candles are an imperial measurement. One foot-candle is equal to approximately 10.76 lux (or 10.764 to be precise). So, if you are using a light meter that only reads in lux, you can divide your reading by 10.76 to convert it to foot-candles.
Foot-candles are important for measuring light intensity in commercial, industrial, and sports lighting. They define the required lighting levels for various environments, ensuring safety and functionality. For example, the Illuminating Engineer Society (IES) recommends a foot-candle reading of 10 for a parking garage. If the lighted areas in your parking garage are reading 7 foot-candles, then you need more lumens to brighten the space.
In the motion picture cinematography field in the US, incident light meters are used to measure the number of foot-candles present. This allows cinematographers to set up proper lighting-contrast ratios when filming. Since light intensity is the primary factor in the photosynthesis of plants, US horticulturalists often measure and discuss the optimum intensity for various plants in foot-candles.
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Foot candles are used to calculate lighting in indoor and outdoor spaces
Foot candles are a unit of illuminance or light intensity, defined as one lumen per square foot. This means that one foot candle is equal to one lumen of light per square foot. Foot candles measure the light that reaches a surface, while lumens measure the quantity of light produced by a light source. As an imperial unit of measurement, foot candles are commonly used in the United States, particularly in architecture, cinematography, horticulture, and commercial and industrial lighting.
In architecture, foot candles are used to calculate lighting levels in indoor and outdoor spaces. Architects use lighting plan software to determine the right amount of lighting for a given space. This software allows architects to simulate foot candle readings on the ground and generate detailed reports on light levels and balance. For example, a dining room measuring 100 square feet, which needs 30-40 foot-candles, will require 3,000-4,000 lumens.
In cinematography, incident light meters are used to measure foot candles, which help cinematographers set up the proper lighting-contrast ratios for filming. In horticulture, foot candles are used to measure the intensity of light for optimal plant growth. Full, unobstructed sunlight, for example, has an intensity of up to 930 foot-candles, while an overcast day produces around 100 foot-candles.
Foot candles are also essential in commercial and industrial lighting to ensure safety and functionality. Organizations like OSHA mandate compliance with foot-candle and lighting standards to maintain adequately lit workplaces. In sports lighting, foot candles are used to ensure optimal visibility for players and spectators. For instance, the Illuminating Engineer Society (IES) recommends a foot-candle reading of 10 for parking garages. If the lighted areas are reading 7 foot-candles, then more lumens are needed to brighten the space.
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Lumens measure the quantity of light produced by a fixture
To understand the relationship between lumens and foot-candles, it's important to know that lumens are a measure of the total amount of light emitted by a source, regardless of direction. In contrast, foot-candles consider the light that reaches a specific surface or area. This distinction is crucial when planning lighting setups, as it ensures that the desired amount of light reaches the intended areas.
For example, let's consider a 100-square-foot dining room that requires 30-40 foot-candles of illumination. To achieve this lighting level, we need to provide 3,000-4,000 lumens. This calculation ensures that each square foot of the dining room's surface receives the desired amount of light. By adjusting the number of lumens, we can control the brightness and lighting levels in the room.
In certain applications, such as cinematography, horticulture, and sports lighting, foot-candle measurements are essential for achieving specific lighting requirements. Cinematographers use foot-candles to set up lighting-contrast ratios, horticulturalists use them to determine optimal light intensity for plant growth, and in sports lighting, foot-candles ensure optimal visibility for players and spectators.
It's worth noting that while foot-candles are commonly used in the US, the metric equivalent is Lux, which measures lumens per square meter. Conversion between foot-candles and Lux is straightforward, with one foot-candle being equivalent to approximately 10.76 Lux.
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Frequently asked questions
There is one foot candle in a lumen per square foot.
A foot candle is a unit of illuminance or light intensity. It is defined as the illuminance of the inside surface of a one-foot-radius sphere with a point source of one candela at its center.
A lumen is the amount of light given off by a light source.
Since one foot candle is equal to one lumen per square foot, you can simply divide the number of foot candles by the square footage of the area to get the number of lumens.
The number of lumens you need for a room depends on the desired number of foot candles and the area of the room. For example, a 100-square-foot dining room that needs 30-40 foot candles will require 3,000-4,000 lumens.
