Tyler Brooks
Lighting terminology can be confusing, with terms like lumens, lux, and foot-candles being thrown around. But what do these terms actually mean, and are foot candles and lumens the same? In simple terms, lumens measure the total amount of light emitted by a source, while foot-candles measure the amount of light from a source that falls on a surface. So, while they are related, they are not the same. Understanding the difference between these two measurements is important when planning an LED lighting project.
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What You'll Learn
- Lumens are the most common measurement when shopping for LED lighting
- Foot candles are a go-to unit of measurement of luminescence
- Lux is the metric measurement of lumens per square meter
- Foot candles are important for reading light levels in a facility
- Lumens don't factor in the distance between the light source and surface area
Lumens are the most common measurement when shopping for LED lighting
Lumens are the standard unit of measurement for LED lighting purchases. Lumens (lm) measure the total amount of visible light emitted by a light source, or its brightness. The higher the number of lumens, the brighter the lightbulb. For example, a standard 100-watt incandescent light bulb produces about 1,500-1,700 lumens. When shopping for light bulbs, it is recommended to compare lumens instead of watts.
However, lumens do not factor in the distance between the light source and the surface area intended to be lit. This is where foot-candles come in. A foot-candle is a unit of measurement of luminescence, or the "level of a light source on a surface." It is equal to about 10 lumens or one lux. Lux is the same as lumen, they both measure luminous intensity. Lux is in the International System of Units (SI), which is the modern form of the metric system. A lux is equal to one lumen per square meter.
Foot-candles are important for reading light levels in a facility. They help determine how much light is illuminating a specific area, taking into account the distance between the light source and the surface. This is especially useful when buying multiple lights, as it helps ensure that each lamp sufficiently illuminates the space without overpaying for more fixtures than necessary.
When it comes to LED lighting, it is important to remember that LEDs are directional, meaning the light is focused in a specific direction. As a result, you need fewer lumens when switching to LED fixtures. There are online calculators available to help determine how many lumens are needed to properly light a space based on room size, ceiling height, layout, and other variables.
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Foot candles are a go-to unit of measurement of luminescence
The unit of foot candles is derived from the basic concept of lumens. Lumens are the amount of light given off by a light source, and they are measured by placing a candle in the middle of a two-foot sphere with a one-square-foot hole in it. The light that comes through the hole is what we define as a lumen.
However, lumens fall short as a measurement when you consider that light needs to shine on an object at a certain distance. For example, 100 lumens is bright enough to read by if the light source is within 6 feet, but it won't be bright enough if the light source is 20 feet away.
Foot candles, on the other hand, are measured at a distance. One foot candle is equivalent to one lumen per square foot, or approximately 10 lux. This means that if you know the foot candle measurement of a light fixture, you can determine how much light will fall on a surface at a specific distance.
This is particularly important when planning lighting for a space, as it ensures that you buy lights that are bright enough to illuminate the space effectively. For example, the Illuminating Engineer Society (IES) recommends a foot-candle reading of 10 for a parking garage. If your parking garage has a reading of 7 foot-candles, then you need more lumens to brighten the space.
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Lux is the metric measurement of lumens per square meter
Lighting terminology can be confusing, with terms like lumens, lux, and foot-candles often being used interchangeably. However, these terms have distinct meanings and applications in the lighting industry.
Lumens are the most common measurement you'll encounter when shopping for LED lighting. They measure the total visible light output from a light source. In simple terms, the higher the lumens, the brighter the light source will appear. For example, if you placed a candle inside a two-foot sphere with a one-square-foot hole and measured the light that came through, you'd get one lumen.
While lumens are useful for understanding the brightness of a light source, they don't consider the distance between the light source and the surface being illuminated. This is where the concept of foot-candles comes into play. A foot-candle measures the light emitted by a candle at a distance of one foot, and it's equivalent to approximately 10 lumens. Foot-candles are crucial for determining the light levels in a facility, as they account for the natural loss of light over distance.
Now, let's delve into the metric measurement of lux. Lux is indeed the metric measurement of lumens per square meter. One lux equals one lumen per square meter, and it represents the illuminance or luminous flux per unit area. In simpler terms, lux measures how much light falls on a surface. For example, if you have 1000 lumens concentrated in an area of one square meter, the illuminance level would be 1000 lux. However, if you spread those same 1000 lumens over ten square meters, the illuminance drops to only 100 lux.
Understanding the relationship between lumens and lux is essential when planning lighting installations. Lux is the standardized unit of measurement for specifying the required light intensity or illuminance in a space. By knowing the lux levels needed for different activities and environments, lighting professionals can determine the number and placement of light fixtures required to achieve the desired lighting conditions. This is particularly crucial in commercial and industrial settings, where specific tasks may demand precise lighting requirements.
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Foot candles are important for reading light levels in a facility
Foot candles are a unit of measurement for luminescence, or the "level of a light source on a surface". They are important for reading light levels in a facility because they indicate how much light is illuminating a given area, rather than just how much light is being emitted by a fixture. This is important for ensuring that areas that require certain light levels, such as offices, manufacturing facilities, and workrooms, are receiving those light levels. Foot candles are also necessary for meeting special lighting requirements, such as in museums, horticulture, and physical security.
When buying lights for a facility, it is important to consider the activities that will be carried out in the space. The work done in a building typically determines the lighting fixtures needed. For example, offices and workrooms require higher light levels to make work easier and reduce eye strain, while hallways and lobbies need lower light levels that are bright enough to move around safely but not so bright as to feel harsh.
Foot candles are measured at a distance, taking into account the distance between the light source and the surface area it is illuminating. This is in contrast to lumens, which measure light output without considering the distance to the surface area. As such, foot candles can help ensure that you buy the right number of lights to sufficiently illuminate your space without overpaying for more fixtures than you need.
To determine the ideal lighting situation for a facility, light meters can be used to measure foot candles. Photometric layouts can also be conducted to show exactly how much light is illuminating the intended surfaces and how much a lighting change can increase foot candle measurements. These tools can help lighting professionals calculate the current lighting situation in a facility and what type of lighting is needed to meet suggested lighting levels.
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Lumens don't factor in the distance between the light source and surface area
Lumens are the most common measurement you'll see when shopping for LED lighting. Lumens (lm) measure visible light from a lamp or light source. The higher the lumens, the "brighter" the source will look. However, lumens fall short as a measurement when you consider that light needs to shine on an object at a certain distance. Knowing that a fixture is 100 lumens doesn't tell you how bright it will be at the distance you intend to use it. For example, 100 lumens is bright enough to read by if the light source is within 6 feet without obstruction, but it won't be bright enough if the light source is 20 feet away.
Foot candles, on the other hand, are a unit of measurement of luminescence, or the "level of a light source on a surface." One foot candle is the amount of light that falls on a surface one foot away from a single candle. Foot candles are measured at a distance—the distance between the light source and the surface area it's illuminating. By knowing a fixture's foot-candle measurement, you can determine how much light will saturate a surface at a specific distance. This can help you calculate if a light fixture is right for you, based on how bright you want your light to be and the distance it will be from whatever it's illuminating.
Lux is another unit used to measure the illuminance or amount of light falling on a surface. 1 Lux is equal to 1 lumen per square meter. Lux is measured using the number of lumens in the bulb, taking into account the amount of visible light falling on the surface. Foot candles and lux are more important than lumens for reading light levels in a facility. You need to know how much light is illuminating the area in question, not just how much light is coming from the lighting fixture.
When planning out an LED lighting project, it is important to understand the difference between lumens and foot candles. While lumens measure light output, they don't factor in the distance between the light source and the surface area you intend to light up. This can be a misleading measurement when buying lights for a workshop, warehouse, or garage. By knowing the foot-candle measurement, you can ensure that the lights you buy are bright enough to light up your space based on a target foot-candle measurement for that space. Additionally, if you're buying multiple lights, buying based on foot candles can help ensure you make the most of each lamp and don't overpay for more fixtures than you need.
There are also free calculators available online that can help you determine how many lumens you need to properly light a space based on room size and type, ceiling height, layout, and other variables. Photometric layouts can also show you exactly how much light is illuminating the intended surfaces and how much an LED lighting retrofit can increase your foot-candle measurements.
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Frequently asked questions
A lumen is the amount of light given off by a light source. The higher the lumens, the brighter the source will look.
A foot-candle is a measure of lumens per square foot. It is the amount of light that falls on a surface one foot away from a single candle.
No, foot-candles and lumens are not the same. Foot-candles are a measure of the number of lumens per square foot, whereas lumens are a measure of the total amount of light emitted by a source.
