An overly-bright or overly-dim room can break what would otherwise be a stunning project. But how does one choose how many luminaires are needed in a space? How does one decide how much light is enough to light up a given room? That’s where light output calculation comes in. This task is particularly crucial in lighting design for commercial, office, and hospitality projects where the light outputs affect the brightness and boost the functionality and productivity of the space. Industry experts often use lumens or footcandles as a reliable way to measure light, and to quantify something that can be very abstract, in turn, makes the planning stage a lot easier.
What are lumens?
Lumens, abbreviated by lm, are a way of calculating the light output of luminaires; they are the industry-standard way of calculating how bright a fixture is. One thing to keep in mind: lumens aren’t interchangeable with watts. Watts measure the amount of power consumed by the light, not the brightness itself. Having a high wattage doesn’t necessarily mean greater output (lumens), but they can go hand in hand.
What is a footcandle?
Footcandles are also a way to measure light, however this is a predecessor to lumens. Before LED or even light bulbs were invented, people used candles for illumination – that’s where foot “candles” comes from. Nowadays, footcandles are widely and most popularly used by lighting professionals to measure the brightness/light intensity in any indoor and outdoor spaces. Experts identify a footcandle as a one square foot square of light a foot away from a light source and on any surface.
The main difference between lumen and footcandle
While lumens are more widely used in Europe, North American peers commonly use footcandles to calculate sufficient light levels.
As with wattage, footcandles are also not interchangeable with lumens. Lumens measure the light output, or brightness, that comes from a light source, while a footcandle measures how much light reaches any given surface a foot away from the light source.
Why are lumen or footcandle ratings important?
During modern planning and design process for lighting of a specific space, it is important to show accurate data and information about the light output of the luminaires. This helps with choosing and placing the luminaires in a lighting design plan.
Because different buildings and spaces require different light levels to satisfy the illuminance requirement and to ensure comfort of the occupants, the lumen or footcandle ratings play an important role to show how much light the space will receive from a given fixture, how many fixtures are needed to provide optimal illumination, and how to position the fixtures in a way that makes sense both aesthetically and logistically for the space.
Converting lumens into footcandles (and vice versa)
A footcandle equals 10.76 lumens. Therefore, using simple math, in order to do a conversion from footcandles to lumens, multiply the amount of footcandles by 10.76.
How to measure light output?
Laboratory tests are often the way to go to measure light out. Because of this, lighting manufacturers often have a testing environment set up in their factory and can provide the results in their product details, descriptions, or, more often, in the specification sheets. This makes it easier for lighting designers to grab the information and apply it to their design projects to decide if a lighting fixture can be used to illuminate a given space.
For on-site testing, there are portable devices to help measure footcandle and lumen.
Light output calculation applications
Different rooms or spaces require different light levels. For this specific reason, having the light output information available allows lighting designers to decide during the planning and design phase the type and number of fixtures needed for a project.
Higher footcandle measurements of about 30 – 50 FC are ideal for office lighting (source: Archtoolbox). Commercial spaces, Conference rooms, boardrooms, libraries and reading rooms can also benefit from this level of footcandle since it helps occupants work easier and reduce eye strain. In such an environment where productivity is key, having the right kind of lighting to enable workers to focus on work is important.
Lower footcandle levels are suitable for hallways and lobbies, where brightness is needed to light up the space just enough to subtly showcase the interior decorations. The ideal range is from 20 – 30 FC (source: Archtoolbox) since hallways and lobbies aren’t areas that require productivity from them, the lighting can be softer, and the footcandles lower.
20 – 50 FC is recommended for lighting in retail settings (source: Archtoolbox), depending on whether the focus is on specific items or to create a pleasant shopping ambience for customers.
Other places can be trickier when it comes to lighting design requirements, and require more detailed lighting solutions. Museums, for example(see Audain Art Museum), need thorough planning so that the interior lighting is bright enough to fully showcase the artwork on display, but not so bright that museum-goers are uncomfortable or can’t enjoy the art due to glare. Finding the perfect in-between can be a bit of a puzzle, but by understanding and using lumens or footcandles to one’s advantage, the planning stage will to a grand end result.
What are lumens and how to apply lumens in lighting design?
An overly-bright or overly-dim room can break what would otherwise be a stunning project. But how does one choose how many luminaires are needed in a space? How does one decide how much light is enough to light up a given room? That’s where light output calculation comes in. This task is particularly crucial in lighting design for commercial, office, and hospitality projects where the light outputs affect the brightness and boost the functionality and productivity of the space. Industry experts often use lumens or footcandles as a reliable way to measure light, and to quantify something that can be very abstract, in turn, makes the planning stage a lot easier.
What are lumens?
Lumens, abbreviated by lm, are a way of calculating the light output of luminaires; they are the industry-standard way of calculating how bright a fixture is. One thing to keep in mind: lumens aren’t interchangeable with watts. Watts measure the amount of power consumed by the light, not the brightness itself. Having a high wattage doesn’t necessarily mean greater output (lumens), but they can go hand in hand.
What is a footcandle?
Footcandles are also a way to measure light, however this is a predecessor to lumens. Before LED or even light bulbs were invented, people used candles for illumination – that’s where foot “candles” comes from. Nowadays, footcandles are widely and most popularly used by lighting professionals to measure the brightness/light intensity in any indoor and outdoor spaces. Experts identify a footcandle as a one square foot square of light a foot away from a light source and on any surface.
The main difference between lumen and footcandle
While lumens are more widely used in Europe, North American peers commonly use footcandles to calculate sufficient light levels.
As with wattage, footcandles are also not interchangeable with lumens. Lumens measure the light output, or brightness, that comes from a light source, while a footcandle measures how much light reaches any given surface a foot away from the light source.
Why are lumen or footcandle ratings important?
During modern planning and design process for lighting of a specific space, it is important to show accurate data and information about the light output of the luminaires. This helps with choosing and placing the luminaires in a lighting design plan.
Because different buildings and spaces require different light levels to satisfy the illuminance requirement and to ensure comfort of the occupants, the lumen or footcandle ratings play an important role to show how much light the space will receive from a given fixture, how many fixtures are needed to provide optimal illumination, and how to position the fixtures in a way that makes sense both aesthetically and logistically for the space.
Converting lumens into footcandles (and vice versa)
A footcandle equals 10.76 lumens. Therefore, using simple math, in order to do a conversion from footcandles to lumens, multiply the amount of footcandles by 10.76.
How to measure light output?
Laboratory tests are often the way to go to measure light out. Because of this, lighting manufacturers often have a testing environment set up in their factory and can provide the results in their product details, descriptions, or, more often, in the specification sheets. This makes it easier for lighting designers to grab the information and apply it to their design projects to decide if a lighting fixture can be used to illuminate a given space.
For on-site testing, there are portable devices to help measure footcandle and lumen.
Light output calculation applications
Different rooms or spaces require different light levels. For this specific reason, having the light output information available allows lighting designers to decide during the planning and design phase the type and number of fixtures needed for a project.
Higher footcandle measurements of about 30 – 50 FC are ideal for office lighting (source: Archtoolbox). Commercial spaces, Conference rooms, boardrooms, libraries and reading rooms can also benefit from this level of footcandle since it helps occupants work easier and reduce eye strain. In such an environment where productivity is key, having the right kind of lighting to enable workers to focus on work is important.
Lower footcandle levels are suitable for hallways and lobbies, where brightness is needed to light up the space just enough to subtly showcase the interior decorations. The ideal range is from 20 – 30 FC (source: Archtoolbox) since hallways and lobbies aren’t areas that require productivity from them, the lighting can be softer, and the footcandles lower.
20 – 50 FC is recommended for lighting in retail settings (source: Archtoolbox), depending on whether the focus is on specific items or to create a pleasant shopping ambience for customers.
Other places can be trickier when it comes to lighting design requirements, and require more detailed lighting solutions. Museums, for example(see Audain Art Museum), need thorough planning so that the interior lighting is bright enough to fully showcase the artwork on display, but not so bright that museum-goers are uncomfortable or can’t enjoy the art due to glare. Finding the perfect in-between can be a bit of a puzzle, but by understanding and using lumens or footcandles to one’s advantage, the planning stage will to a grand end result.