What are Foot Candles?
In the world of lighting, there are several methods to measure a light’s output. While in the past this was typically measured simply by its wattage rating, the process is much more sophisticated today. As LED technology has rapidly evolved, methods to quantity a lights output have improved as well – allowing for more efficient and effective lighting plans for facilities.
Generally speaking, the two main ways for measuring lighting intensity are lumens and foot candles (FC). While both of these methods measure total light output, the way they are measured is quite different. Lumens is the most straightforward, as it is a measurement of the amount of light produced by a lighting fixture (at the fixture itself). Foot candles on the other hand measure light intensity at specific distances away from the light source, such as floors, desks, walls, etc.
Why are FC ratings Important?
Because the modern planning process for building lighting configurations requires precise data and information regarding the performance characteristics of specific lighting fixtures, a lights foot candle measurement is by far the most important measurement in the eyes of photometric planners. This provides the most accurate data possible, and allows for the precise selection and placement of lighting fixtures in a lighting plan.
This accuracy is vital due to several factors, namely the variance in the distance of light fixtures from the areas they are illuminating. As the distance between the light fixture and area being illuminated increases, the FC rating will decrease accordingly. Because all buildings have some sort of a minimum light intensity requirement for a particular area, those designing lighting plans will be looking for fixtures that produce the appropriate foot candle rating at the specified distance they are from the area they are illuminating.
In most cases, this is usually the vertical distance from the fixture mounted on a ceiling to the floor below, although it can also be a semi-horizontal distance such as a flood light illuminating a sign. Combined with beam angle, selecting a fixture with the right foot candle rating for the application is the last major component of a proper lighting plan. For most plans, it is simply a matter of determining the appropriate number of fixtures in the right arrangement in order to provide the correct amount of lighting for the area.
Foot Candle vs. Lux
Both Foot Candle and Lux are types of light output measurements, just on different scales. Lux is an SI derived unit of measurement used on certain applications that dictate the use of SI units for all project engineering. Converting the two units is simple, as 1 foot candle equals 10.77 lux and 1 lux equals 0.0929 foot candles. Below a calculator to help with this conversion process:
Foot Candles =
Recommended FC Levels
While the appropriate foot candle levels for an application can be subjective, there is a generally accepted amount for standard lighting applications. These applications can vary quite a bit however in their requirements. For instance, a large big box retail store will not have the same lighting requirements as a warehouse of the same size and dimensions.
Even though these two buildings may have the exact same square footage and ceiling heights, the lighting requirements differ considerably due to the intended usage of the facilities. It is for this reason that a simple one size fits all take on lighting is ill advised and unrealistic for most end users. In fact, OSHA even sets forth minimum lighting requirements for different workplaces in order to ensure a safe foot candle rating for the application.
Below are a list of the most common foot candle ratings for different facilities: