Jessie Taylor
Foot-candles are a unit of measurement for light intensity, predominantly used in the United States. One foot-candle is defined as the amount of light emitted by a candle that illuminates a one-foot square area with one lumen of light. Foot-candles are used to ensure that areas requiring certain light levels are receiving them, such as in electrical construction, cinematography, photography, and horticulture. To measure foot-candles, a light meter is placed on a flat white surface perpendicular to the light source, and the reading is taken from one foot away from the source.
| Characteristics | Values |
|---|---|
| Definition | Foot-candles is a measurement of light intensity |
| Unit of Measurement | Foot-candle, fc, lm/ft2, or ft-c |
| Conversion | 1 lux is equal to 0.092903 foot-candles |
| Measurement | Foot-candles measure the amount of light that falls on a surface that is 1 foot away from a singular candle |
| Purpose | To ensure that areas that require certain light levels are receiving those light levels |
| Examples | Museums, horticulture, movie and video shoots, electrical construction, offices, manufacturing facilities, workrooms, hallways, lobbies, factories, gyms, laboratories, commercial kitchens, etc. |
| Tools | Light meters, photometric modelling software |
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What You'll Learn
Understanding foot candles
In modern usage, foot candles are used to ensure that specific areas receive the required light levels. This is particularly important in electrical construction, office design, and horticulture. For example, workspaces like offices and manufacturing facilities require higher foot-candle measurements to enhance task performance and reduce eye strain. On the other hand, hallways and lobbies need lower foot-candle readings as the lighting in these areas serves mainly to showcase decor and ensure safety.
Museums are another setting where foot-candle measurements play a crucial role. Curators must carefully control light levels to create the desired ambiance and protect light-sensitive artefacts. Similarly, in horticulture, precise foot-candle readings are necessary to ensure that plants receive the appropriate amount and type of light for optimal growth.
Foot candles are also widely used in cinematography and photography. Filmmakers and photographers use light meters to gauge the light in a scene and make creative and technical decisions accordingly. Additionally, any business or organisation with physical security requirements, such as cameras and doors, must also consider foot-candle readings in these sensitive areas.
To measure foot candles, light meters are commonly used. These meters are placed on the illuminated surface to measure light intensity. While foot candles are predominantly used in the United States, other parts of the world, like Europe, use the SI-derived unit "lux," which measures light intensity over a one-metre square area. The conversion factor between the two units is approximately 0.092903 (foot-candles per lux).
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How to measure foot candles
Foot candles, or fc, are a unit of measurement for light intensity, or illuminance. One foot-candle is defined as the amount of light produced by a candle that is one foot away from the subject. In other words, it is a measurement of the amount of light that reaches a surface area, rather than the light reflected from it (luminance).
Foot candles are especially useful for ensuring that areas requiring certain light levels are receiving those light levels. For example, offices, manufacturing facilities, and workrooms need higher foot-candle measurements to make work easier on the eyes, while hallways and lobbies need lower foot-candle readings.
To measure foot candles, a light meter is the best tool. Light meters are available from many manufacturers at various price points, from $20 to $200 or more. The right meter is one that is accurate and fast. Most light meters will output their readings in foot-candles or "lux," the SI-derived unit that measures light intensity over a one-metre square area. To convert lux to foot-candles, divide the lux value by 10.764.
For those who want to measure foot candles without a light meter, one source recommends using a candle, a sphere with a two-foot diameter, and a flat wall. First, cut a hole that measures one square foot in the centre of the sphere. Then, place the candle in the middle of the sphere and position the sphere so that it is 0.30 meters (one foot) away from the wall. The light that shines through the hole and onto the wall is one foot-candle.
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Lighting requirements
Several factors determine the recommended foot-candles for a specific area, including the age of the occupants, the nature of the task being performed, the background brightness of the space, and the level of light or lux provided by fixtures. For instance, older adults may require brighter lights than younger ones to accomplish the same task. Lighting levels are essential considerations for facilities management, as more detailed tasks necessitate higher foot-candles than simpler tasks.
Residential spaces generally require fewer foot-candles than commercial and industrial spaces. Bedrooms, living rooms, and dining rooms should utilize more ambient lighting for a cozier aesthetic. 10-20 foot candles often work well for areas like these. Commercial spaces (offices, retail stores, and educational institutions) require slightly brighter lighting for greater productivity and visibility. Aim for approximately 30-50 foot candles to ensure a well-lit environment.
Industrial settings, such as workshops, warehouses, and factories, tend to require higher foot-candle levels due to their detailed, precision-focused tasks and safety requirements. It is recommended to have lighting that’s at least 75-100 foot candles – but upwards of 200 foot candles for tasks that demand more specific tasks, like medical laboratories.
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Light meters
Foot-candles are a measurement of the amount of light that falls on a surface that is one foot away from a singular candle. It is predominantly used in the United States, while other parts of the world, such as Europe, use the SI-derived unit "lux", which measures light intensity over a one-metre-square area.
To measure foot-candles using a light meter, position the light meter at the point where you want to assess the light level, with its sensor facing the illumination source directly. For example, to measure the light falling on a work desk, you would place the device on the desk surface. The sensor should have a clear, unobstructed view of the light source. Take measurements in a horizontal position, as foot-candle measurements assume a surface directly receiving light.
It is important to note that light intensity changes throughout the day, and common issues can distort readings, such as when the meter is exposed to multiple light sources. To get a reliable reading, you should take multiple measurements at different times and calculate an average.
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Foot candles in cinematography
Foot candles are a unit of measurement for light intensity, or illuminance. It is defined as one lumen per square foot. In other words, one foot-candle is the amount of light produced by a candle placed one foot away from a surface. This unit of measurement is especially useful in cinematography to determine the amount of light falling on a subject. Cinematographers use light meters to measure foot-candles and adjust lighting setups accordingly.
Foot candles are a non-SI unit of measurement, mainly used in parts of the world where United States customary units are followed. In cinematography, foot-candles are often used alongside lux, which is the SI unit of illuminance. Lux measures the amount of light falling on a one-metre square surface, whereas foot-candles measure the amount of light on a one-foot square surface. Cinematographers may use either metric depending on the set and location.
To measure foot-candles, cinematographers use light meters that display foot-candles, lux, and f-stops simultaneously. This allows them to monitor lighting values and adjust their camera's exposure accordingly. By experimenting with different light setups and distances, cinematographers can create the desired lighting effects for their scenes.
Foot candles are crucial in cinematography as they help determine the lighting requirements for different scenes. For example, a brightly lit office scene would require higher foot-candle measurements, while a dimly lit hallway scene would call for lower foot-candle readings. Cinematographers can also use their knowledge of foot-candles to emulate lighting from references or recreate specific lighting conditions.
Additionally, foot-candle measurements are essential for filming in locations with specific light requirements. For instance, museums need controlled light levels to protect artefacts, and cinematographers must adhere to these requirements. Horticulture is another field that demands precise foot-candle readings to ensure plants receive the appropriate amount and type of light. Cinematographers can use foot-candles to ensure their lighting setups do not cause damage or adverse effects in such locations.
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Frequently asked questions
A foot-candle is a unit of measurement for light intensity, or illuminance. It measures the amount of light that falls on a surface that is one foot away from a singular candle.
To convert lux to foot candles, divide the lux value by 10.764.
Foot candles are used in the imperial measurement system, while lux is used in the metric system.
The idea of using foot candles is to ensure that areas that require certain light levels are actually receiving those light levels.
Foot candles are typically measured using a light meter.
