What Is a Foot Candle? How Many Do I Need?

If you’ve ever dabbled in lighting concepts, you may have encountered the term ‘foot candle.’ A foot-candle measures the intensity of light falling on a surface, equivalent to the light cast by one candle from one foot away. This unit is frequently used in architecture, lighting design, and film industries.

But why is understanding foot candles important? Beyond its fundamental role in these professions, foot candles allow us to determine the amount of light required for various environments accurately, be it an office space, a residential interior, or a public sidewalk. Being well-versed in this illuminative unit is crucial to creating comfortable, efficient, and practical lighting solutions, forming the bedrock of multiple other lighting aspects.

Deep Dive Into the Concept of “Foot Candle”

Foot candle measures light intensity, or illuminance, on a given surface. Rather poetically, the name derives from the amount of illumination a single candle produces from a one-foot distance. To make it more concrete, imagine holding a birthday candle a foot away from your open book – the light it provides over that specific area is a one-foot candle of illumination.

But how does this translate into practical usage, particularly in lighting design and planning?

Foot candles are benchmarks for gauging appropriate lighting levels in various spaces. For instance, an office desk is often lit at about 50-foot candles, while a hallway might require only 10. The exact number depends on the specific tasks being performed, the age of people using the space, and other variables. Simply put, by measuring and planning according to foot candles, lighting designers can tailor the lighting levels to ensure both comfort and function, ranging from the ambient mood of a restaurant to the bright clarity required in an operating room.

Despite sounding somewhat old-fashioned to the modern ear, the term’ foot candle’ is significant in lighting history. Introduced in the late 19th century, it formed the basis for international standards in light measurement. It saw extensive use during an era when the primary light source was the humble candle. While other light measurement units like ‘lux’ are more commonly used globally today, the foot candle still holds sway in the United States and is friendlier for those outside the profession to understand. Despite evolving trends and technologies in lighting, the charming foot candle remains a steadfast icon illuminating our evaluation of light.

Foot Candles to Lumens: Understanding the Relationship

To understand how foot candles relate to another common term in lighting, lumens, it’s important to distinguish between them. While foot candles measure the light intensity a surface receives, lumens quantify the total amount of light produced by a light source. Lumens essentially communicate how bright a lamp, or bulb, will be – think of it as the ‘light output.’

Connecting foot candles with lumens involves some science, courtesy of a mathematical equation. Each foot candle is equivalent to approximately 10.764 lumens per square foot. To put it into a formula, multiply the number of foot candles by 10.764 to get lumens per square foot. Conversely, to find the number of foot candles from lumens, you can divide lumens by 10.764.

This relationship between foot candles and lumens is beneficial in practical scenarios. Suppose you’ve got a light bulb that emits 800 lumens, and the targeted illumination area is your work desk with a surface area of 15 square feet. You could divide those 800 lumens across the 15 square feet, which yields approximately 53 lumens per square foot. To convert this to foot candles, simply divide this number by 10.764. The result of around 5-foot candles indicates a dim workspace, suggesting the need for a bulb with a higher lumen output.

Observing how foot candles and lumens interact elucidates these units’ complementary and distinct aspects, providing a clearer perspective on how lighting affects our spaces. With such knowledge, extracting the maximum utility from our light sources while maintaining eye-friendly environments becomes substantially easier.

How to Measure Foot Candles

Measuring foot candles is a direct yet nuanced process. Typically, this is carried out using light or illuminance meters. These handheld devices, available in analog and digital variants, capture the amount of light on their sensors, outputting the values in foot candles or lux. Some advanced smartphone apps can also provide a reasonable estimate of foot candles if a dedicated light meter is unavailable.

The general procedure for measuring foot candles is straightforward: you position the light meter at the point where you want to assess the light level, ensuring its sensor faces the light source directly. For instance, you would place the instrument on the desk surface to measure the light falling on a work desk. Remember, the sensor should not be shaded or blocked in any way – it needs a clear, unobstructed outlook toward the light source.

Despite the apparent simplicity, measuring foot candles can occasionally be tricky, beset by common pitfalls that might distort the results. One frequent issue arises when the meter faces multiple light sources – say, a combination of window daylight and interior artificial lighting. Remember, the meter records cumulative light intensity, which might give inaccurate readings if you’re testing for a single source. In such cases, it’s advisable to block off or turn off additional lights and repeat the measurement.

Another potential challenge is paying attention to the fact that light intensity fluctuates throughout the day. To get a reliable reading, it’s wise to take several measurements at different times and compute an average. This approach can mitigate issues arising from changing natural light or varying intensity of artificial light sources.

Understanding how to measure foot candles and anticipate and overcome potential issues ensures more accurate, effective, and user-friendly lighting designs. As with many things, knowledge and careful application can turn illuminating ideas into reality.

Interpreting Footcandles: From Theory to Application

As we’ve learned, foot candles are pivotal for quantifying and understanding lighting requirements. However, the application and interpretation of foot candles extend beyond simple measurement—it guide us to achieve optimal lighting conditions for various activities and settings.

The number of footcandles depends mainly on the nature of the tasks being performed. Higher precision activities, like drafting or intricate handwork, often demand 50-75 footcandles. In contrast, less visually intensive tasks, such as casual reading or walking through a hallway, require considerably fewer footcandles, usually around 10-20.

Similarly, foot candle requirements differ based on settings. An office workspace, where activities like reading, writing, and computer work are prevalent, may require around 30 to 50-foot candles for comfort and efficiency. On the other hand, a residential kitchen—where safety is paramount but where glare must be minimized—might best function at around 30-75-foot candles, depending on specific zones. Ideally, a cozy reading area would be lit with about 30-50 foot candles, balancing sufficient light to prevent eye strain and a relaxing atmosphere.

In a broader sense, footcandles are instrumental in effective lighting planning. It informs designers about the intensity and placement of lights and enables anyone to customize their surroundings based on their needs and tasks. Understanding foot candles allows us to strategize energy usage, balancing sufficient light and energy conservation. By allowing us to match the lighting conditions with the needs of the space, foot candles truly elevate the art and science of lighting design.

Lumens to Foot Candles: Converting and Comparing

As we walk between the realms of lumens and foot candles, understanding how to convert between these units can provide a fuller picture of our lighting scenarios. Remember, lumens measure total light output, while foot candles consider the light intensity received by a surface.

To convert lumens to foot candles, start with the lumen rating of your light source, then divide it by the surface area in square feet you intend to illuminate. This calculation gives you lumens per square foot. To obtain foot candles from this value, divide by the conversion factor, 10.764.

Consider an example where you’re using a 1200-lumen lamp to light a space of 20 square feet. This gives you an illumination of 60 lumens per square foot. Dividing by 10.764 results in approximately 5.57-foot candles. This lower foot candle level suggests a larger lumens output or a smaller area could benefit the space’s intended function.

In reverse, if you know the foot candles required and the surface area, you can calculate the lumens necessary. Multiply the foot candles by the area and then by 10.764 to get the lumens output needed.

Comprehending this conversion is not merely an academic exercise—it serves practical applications. It helps interpret the lighting specifications of products, ensuring an educated purchase. It lets you tailor your lighting solutions for optimal brightness, energy efficiency, and mood setting.

IES Recommended Lighting Levels: The Role of Foot Candles

The Illuminating Engineering Society (IES) is a reputed authority that provides guidelines on recommended lighting levels for various settings meticulously delineated in foot candles.

Foot candles play an essential role in these recommendations by offering a user-centric perspective—focusing on the light as received and experienced by the human eye in a given environment. This perspective makes the standards practical, application-oriented, and easily understandable.

Before and after images of LED lighting project at General Mills in Cedar Rapids, Iowa

For example, the IES suggests a range of 30 to 50 foot candles for typical office work or around 10-foot candles for general outdoor nighttime lighting. A museum showcasing acceptable, intricate art could require 30 to 50-foot candles.

These guidelines are ideal starting points for lighting design, facilitating spaces that are visually comfortable and conducive to the tasks. However, it’s also important to consider additional factors like natural light, the age of the occupants, and the presence of reflective surfaces. Understanding foot candles and the IES recommendations empowers individuals and professionals alike to create well-lit spaces that are both performance-oriented and environmentally considerate.


Embarking on a comprehensive exploration of foot candles, we’ve illuminated this lesser-known yet crucial component of lighting spaces—from its definition to its practical applications and its role in the guidelines from bodies like the Illuminating Engineering Society (IES). Foot candles control our surroundings, enabling us to tailor the lighting to optimize productivity, ambiance, and comfort. It is intertwined with our daily lives, influencing professional workspaces, home interiors, and public spaces.

In the end, understanding foot candles transmutes abstract lighting concepts into tangible, actionable knowledge. It allows us to make informed lighting decisions, shaping our environments with a precise blend of functionality, comfort, and aesthetics. This understanding truly puts the power of light in our hands, encouraging us to make enlightened, illuminative choices with confidence and clarity.If you have a specific question about suggested light levels, contact WattLogic, who will help guide you every step of the way.