104. Guide To Understanding Footcandles in Lighting

Lighting is highly important in our daily lives. It can influence productivity, safety, and comfort in different environments. When it comes to choosing the right lighting for a space, one important but often overlooked metric is the footcandle. We are offering this guide to provide an in-depth understanding of footcandles, foot candle lux, the importance of lighting selection, and which footcandle targets are best in different applications.

What is a Footcandle?

A footcandle (FC) is a unit of light intensity or illuminance measuring the amount of light that falls on a surface. More accurately, one footcandle is defined as the illuminance on a one-square-foot surface from a uniform source of light that is positioned one foot away. This is the equivalent of one lumen per square foot. The term comes from early forms of lighting, in which the light source was typically a candle. Even more simply put, a footcandle reading tells us the amount of light that reaches a given surface or workspace. 

Why Are Footcandles Important When Making a Lighting Selection?

Footcandles are a critical factor in lighting design. These include:

• Adequate Visibility—Spaces need to be sufficiently lit for the tasks that will be performed within them. Proper illuminance ensures this. How much light is needed per square foot is not just based on the area’s size but also on what will be happening and in what manner. For example, an office will need lighting levels that are different from those of a warehouse.
• Safety and Comfort—Many people overlook the idea that lighting levels can alter safety and comfort. Appropriate lighting levels reduce the risk of accidents and contribute to safety. Regarding comfort, the right illuminance can prevent eye strain in a setting.
• Energy Efficiency—Knowing and understanding footcandle requirements will help in designing energy-efficient lighting systems for any space. By focusing on footcandles, you can ensure that a space is not over-lit or underlit while still conserving energy.
• Aesthetic Appeal – Having the right amount of lighting can set the vibe of a space. In fact, choosing and creating appropriate lighting highlights architectural features that may otherwise be overlooked.
• Standards Compliance – Many industries and regions have specific standards when it comes to lighting. These regulations must be met to meet the necessary codes. These standards tend to be defined in terms of footcandles and lux.

Factors Influencing Footcandle Requirement

While we know that footcandle requirements are important, the space is what truly influences what is required. Many of these requirements for a given space are determined by the IES footcandle recommendations. The IES is the Illuminating Engineering Society, which asks installers and designers to consider the following factors.

• Type of Activity—It may seem obvious that different activities require different levels of illumination, but this is often overlooked. For example, highly intricate tasks like surgery or fine assembly will require higher footcandle levels than general tasks like resting or walking.
• Age of Occupants in an Area – As we age, more illumination may be necessary for general tasks. This is just because eyesight often begins to fail, and seeing clearly requires more light. This means that spaces frequented by seniors may need a higher footcandle level than typical.
• Nature of the Space – The design and function of a space will influence its lighting needs. For example, a theater will require variable lighting in order to set different moods, but a library would need uniform lighting to allow for reading in all areas.
• Reflectance of Surfaces—The materials chosen to fill a space will also help determine the type and level of lighting needed. The color and materials of stationary items can reflect light in different ways. Light-colored, reflective surfaces can enhance the effectiveness of lighting so that footcandle levels can be reduced while still having the same effect as higher levels on darker surfaces.
• Availability of Natural Light—When a space has ample natural light, fewer footcandle lumens are necessary. Artificial lighting is great for darker spaces, but natural light can reduce the need for artificial options. That said, the time of day and season can drastically affect the amount of natural light that is available in a space, which should be accounted for when creating a space.

DOWNLOAD: Footcandle Lighting Guide as recommended by the IES (Illuminating Engineering Society)

Calculating Footcandles for a Space

To determine the appropriate footcandle levels for a given space, use the following steps:

1. Identify the Activity: Think about the primary activity for a space, whether reading, shopping, processing, or something else. Refer to the chart above to check the recommended footcandle targets for the main activity.
2. Measure the Space: Next, calculate the total area of the space in square feet.
3. Determine the Lumen Requirement: Once you find the area of the space in square feet, multiply the area by the recommended footcandle level to determine the total of required lumens.
4. Select Light Fixtures: Choose the style of light fixtures that can provide the necessary lumens and that work within the space. Make sure also to consider the efficiency and placement of each fixture to ensure uniform lighting in the space and avoid dark corners.

Example: Suppose you need to determine the lighting for a kitchen that is 1,000 square feet. The recommended footcandle level for a kitchen in the hospitality industry is 40-50 fc. So, to calculate, you would:

Area: 1,000 sq. ft.

Recommended Footcandle Level: 40-50 FC

Total Lumens Required: 
For 40 FC: 1,000 sq. ft. x 40 fc = 40,000 lumens
For 50 FC: 1,000 sq. ft. x 50 FC = 50,000 lumens.

Select lighting fixtures that can provide a total of between 40,000 and 50,000 lumens to use in the space.

Other Considerations

When choosing lighting, there are more considerations than those listed above. These include:

• Lighting Control Systems – The use of lighting control systems like dimmers or occupancy sensors allows you to optimize lighting levels and enhance energy
  efficiency. These systems adjust or can be adjusted based on time of day, occupancy, availability of natural light, and even desired mood.
• LED Lighting—Light-emitting Diode (LED) technology has revolutionized the lighting industry by providing high lumens per watt while reducing energy consumption. The initial cost may be higher, but a longer lifespan means savings in the long term.
• Light Quality – Beyond footcandle lumens, consider color temperature and the color rendering index (CRI) of light sources. Warmer color temperatures in the 2700K to 3000K range create a cozier atmosphere, while cooler temperatures in the 4000K – 5000K range are better for task-oriented environments. A high CRI of 80+ will ensure accurate color representation.
• Maintenance – Keeping up with the maintenance of lighting systems regularly, including fixture cleaning and replacement of bulbs, will create consistent lighting levels while prolonging the lifespan of the system.
• Human-Centric Lighting—Consider designing lighting systems that support human health and well-being. This form of lighting adjusts the color temperature and intensity of light throughout the day to mimic natural daylight patterns. This improves mood, productivity, and alertness, as circadian rhythms are supported.
• Codes and Standards – It is important to adhere to a space's local energy codes and standards. Check out the International Energy Conservation Code (IECC) and ASHRAE standards, as they may dictate the maximum allowable lighting power densities (LPD) and other requirements.

Health Impacts of Lighting

Choosing lighting for a space is not just about the space but also about the humans that are in that space regularly. This applies to residential and business spaces. When considering the human aspect of lighting, think about the following.

• Circadian Rhythm Regulation – Our internal biological clocks are highly influenced by light exposure. Bright, cooler lighting in the morning helps people wake up, while warmer lighting in the evening supports winding down. Choosing the wrong lighting can disrupt this rhythm and negatively affect productivity.
• Visual Comfort—Excessive or insufficient lighting can cause health problems, such as eye strain, headaches, and discomfort. To ensure the proper footcandle levels, use lighting with strong glare control and even distribution. Consider task lighting to create focused light for specific activities.
• Psychological Effects—Lighting can affect mood and mental health. Bright natural light can have positive effects and enhance energy levels, making it perfect for work environments. Proper lighting can reduce stress, enhance concentration, and improve well-being for employees, patients, students, and others.

Wrapping Up

Understanding footcandles and their importance when considering lighting selection is essential for creating well-lit yet comfortable and efficient spaces. By considering a space's specific needs, like activities and recommended footcandle targets, you ensure an optimal lighting design. Furthermore, implementing advanced lighting control systems and maintaining lighting quality will further enhance effectiveness.

This guide has provided a comprehensive overview of footcandles while offering valuable insights for architects, facility managers, and designers who are involved in lighting selection and design. If you adhere to these principles, you can effectively create environments that enhance safety, well-being, and productivity. And if you need guidance planning your lighting project and selecting the right product for your application, please contact our team at (800) 553-2112 or email [email protected].