What is a Foot Candle & How Is It Measured?

If you're considering upgrading the lighting on your property, chances are you've encountered some confusing terminology while doing your preliminary research. If you're unfamiliar with how lighting is measured, attempting to abide by the illumination recommendations set by OSHA and the IES may seem overwhelming.

One term that throws off a lot of our customers is "foot candle," as it's one you will rarely hear in everyday conversation. To help you make the best decisions for your property, we've put together this easy guide on what a foot candle is and how it's measured. If you have any questions or want to learn more about a lighting upgrade for your property, don't hesitate to call us at (754) 200-5872.

Metal roof structure of a large building, indoors. Built-in windows at the top for lighting

What is a Foot Candle?

A foot candle is a measurement of light intensity in an area. It does not measure the intensity of light at its source but instead measures the brightness of the space being lit.

One foot candle is defined as the illumination on a one-square-foot surface from a consistent light source. One foot candle is enough light to saturate a one-foot square with one lumen of light.

Foot candles are the most common unit of light measure that lighting professionals use to calculate light levels in businesses and outdoor spaces.

What Is the Purpose of a Foot Candle?

A foot candle is commonly used to determine sufficient lighting levels for a given space. The measurement helps determine help determine if an area is receiving adequate lighting.

Why Are They Important?

Adequate illumination is vital for both safety and wellness. Properly lit outdoor spaces experience lower levels of crime and property damage. Having the right lighting in offices and classrooms reduces eye strain and guards against accidents caused by low visibility.

A uniform measurement that can be used in any scenario is essential to ensure all guidelines and requirements are followed and all private, public and commercial spaces are properly lit.

How To Measure Foot Candles

When measuring a foot candle, you would use Photometry, a way to measure light as it is perceived. This differs from “radiometry,” which measures all forms of radiant energy (including light) in absolute terms. For example, putting a lampshade over a light bulb will reduce its photometry readings, but NOT its radiometry readings.

Photometry is the measurement of light as our eyes interpret it, and businesses and organizations of all kinds need to understand it to curate their lighting.

The best tool for your photometric, and thus your foot candle readings, is a sensitive light meter. Light meters are inexpensive and can be purchased to measure light in either Foot Candles or Lux units.

To measure foot candles, place a light meter on the surface that is being lit.

How to Calculate How Many Lumens Are in a Foot Candle?

One foot candle is equal to one lumen of brightness per square foot, measured at least a foot from the light source.

One foot candle equals 10.76 lumens. A lumen is considered the same as lux, which is what most modern light meters calculate their measurements in. To convert your foot candles to lumens, you will need to take the number of foot candles measured and multiply by 10.76 to get the number of lumens.

How to Calculate How Many Watts Are in a Foot Candle?

There are 1.578 watts per square centimeter in one foot candle of light. If you’re looking to convert a higher number of foot candles into watts, use the formula below. It’s important to note that this formula measures watts per square meter, so your numbers will be smaller.

Number of foot candles x 10.76 (lux.) x 0.001496

For example, there are .16 watts per square meter (or 16 foot candles per square centimeter) in 10 foot candles.

How Do You Read Foot Candles?

It’s possible to measure foot candles using a light meter directly placed on the surface that is being illuminated. Light meters are inexpensive, widely available, and most give you the option of reading in either lux or foot candles, saving you the hassle of doing the conversion mathematics yourself.

You should use a light meter on the most important surface. For commercial applications, you may want to check the light intensity on the floor so that any potential hazards are visible. For sporting venues, you’ll want to measure the court’s surface so that lighting uniformly reflects onto the lines.

How Many Lumens Does a Room Need?

To determine the needed lumens, you must multiply your room’s square footage by your room’s foot candle requirement. For example, a 100-square-foot living room, which requires 10-20 foot candles, will need 1,000-2,000 lumens. A 100-square-foot dining room, which needs 30-40 foot candles, will need 3,000-4,000 lumens.

Foot Candle Recommendation by Application

Public areas surrounded by darker areas generally require at least 2 to 5-foot candles, or 20 to 50 lux, while typical offices and classrooms without highly detailed work will need 10 to 20 foot candles, or 200 lux. Light in public areas should typically be lower and warmer, while work areas should receive lots of bright light.

Depending on a space’s intended purpose, there are different foot candle recommendations. OSHA and IES general guidelines help you understand what lighting is needed and where.

2-10 Foot Candles

2-10 foot candles is the appropriate light level for low-lit outdoor spaces such as walkways, train stations, parking lots, and parking garages.

10-25 Foot Candles

10-25 foot candles would be an appropriate light level for multi-purpose rooms such as a school cafeteria or auditorium, parcel distribution facilities, gun ranges, and auto dealerships.

25-40 Foot Candles

25-40 foot candles describe the light levels in airports, indoor gymnasiums, workshops, and indoor basketball courts.

40-55 Foot Candles

40-55 foot candles of lighting can be found in factories, gyms, gymnastics studios, and painting booths.

60+ Foot Candles

60+ foot candles is the appropriate lighting level for commercial kitchens, office spaces, chemical laboratories, and operating rooms. These rooms need excessively bright lights to keep operations functioning properly.

OSHA Lighting Requirements

The foot candle is OSHA’s preferred unit of measurement. Title 29 of the Code of Federal Regulations, section 1926.56, sets the light’s foot candle requirements for various areas.

As a general rule, lighting should be evenly distributed through all workplaces, without interruption, so that workers can comfortably see and move around without straining their eyes.

OSHA recommends specific foot candle breakdowns for various types of work:

  • First-aid stations, offices, and infirmaries: 30 foot candles
  • General construction plants and shops: 10 foot candles
  • General construction area: 5 foot candles
  • Warehouses, walkways, corridors, exits, and other indoor spaces: 5 foot candles
  • General underground work areas, including shafts and tunnels: 5 foot candles
  • Concrete placement, waste areas, loading platforms, active storage areas, field maintenance areas, refueling areas, and excavation sites: 3 foot candles

Underground work areas do have one exception. When drilling, mucking, and scaling is performed, at least 10 foot candles are required. This lighting can usually be achieved with the installation of overhead lights, though sometimes other forms of lighting are permitted, for example- cap lights in mines.

OSHA’s 1910.305 Emergency Lighting and Lighting Installation Standards

OSHA standard 1910.305 governs the installation requirements for lighting implements.

Unless otherwise specified, these rules, which apply to permanent light fixtures, also apply to temporary fixtures. All grounding conductors need to be safely grounded where necessary. No wiring systems should be installed in ducts that transport dust or flammable vapors.

Most restrictions on temporary lighting apply to implements under 600 volts. These can only be used in remodeling, repair, emergency work, or similar tasks.

Standard 1910 governs the use of emergency lighting (i.e., lighting from a reserve source, triggered when general lighting becomes unavailable due to power failure).

The good news is that most of the same rules that apply to general lighting also apply to emergency lighting, except for temporary electrical installations. Temporary lights of more than 600 volts may only be used in emergencies, tests, or temporary construction activities.

IES Foot Candle Requirements

The Illuminating Engineering Society of North America (IESNA) has created a handbook that recommends the level of foot candles that should be aimed for in each room or outdoor area of a home or business.

In terms of a home, the IES recommends 20 to 30 foot candles for bedrooms and up to 75 foot candles for kitchens, where more activity, which requires better visibility, occurs.

Regarding commercial spaces, the IES recommends that parking garages have around 5 to 10 foot candles, offices between 30 and 50, and for laboratories where precise measurements are needed, between 75 and 120 foot candles.

Have More Questions About Commercial Lighting Solutions?

If you have any questions about commercial lighting solutions, our team of experienced commercial electricians is here to help. We have helped property owners all over Florida to lower maintenance and energy costs by upgrading or retrofitting their existing commercial lighting systems.

Suncoast Power has been locally-owned and operated for more than three decades. We specialized in a wide range of lighting solutions such as LED lighting installations, LED retrofits, and comprehensive lighting audits.

Call us at (754) 200-5872 or fill out our online contact form to schedule a lighting assessment with one of our electrical experts. Our representatives are standing by to answer any questions you may have and get you booked!