Measuring Industrial Illumination in Foot Candles
Exact lighting measurements enable warehouse managers to meet OSHA and other industrial regulations, and help to create a safer workplace. If you check the OSHA standards that govern illumination requirements, though, you may encounter an unfamiliar term: foot-candles. It may sound unscientific, but the science behind the term gets fairly involved.
Unfortunately, you can’t define foot-candles without understanding a few preliminary technical terms. First, we need to define another unit of light measurement, the "lumen," and to define the lumen, we have to explain the "candela." Let the definitions begin:
The candela is the base unit of luminous intensity, roughly equal to the amount of light generated by a classic wax candle. There is a more technical definition — monochromatic radiation with a frequency of 540 x 1012 hertz and a radiant intensity of 1/683 watts per steradian — but we find that the light of one candle is easier to imagine.
The lumen is the standard unit of luminous flux used by the International System of Units (SI). For our purposes, “luminous flux” basically means the brightness of visible light. One lumen is equal to one candela facing a given direction.
Now that we understand these concepts, we're ready to define a foot-candle. Put simply, a foot-candle is equal to one lumen per square foot, abbreviated as lm/ft2.
Note that this measurement is peculiar to the United States; most other industrialized countries measure light output in "lux," which describes one lumen per square meter.
How to Measure Foot-Candles in Warehouses and Other Environments
Light levels can fluctuate within a given space, but that’s okay. You just need a minimum level of illumination to meet OSHA standards. To obtain this measurement, use a light meter; most industrial models can be set to display the metric unit, lux, or foot-candles.
Once you’re sure your light meter is set on foot-candles rather than lux, take measurements in spaces where a given task will be completed. For instance, if you’re testing the illumination at an order-packing station, position the light meter at the surface of the desk or lift-table.
If you’re curious as to how different light sources affect the total illumination in your warehouse, just point the light meter at the individual bulb; the reading will reflect the intensity of that lamp. You can use portable work lights for a quick fix if you find low light levels, although eventually you’ll probably want to find a permanent lighting solution.
Foot-Candles in the OSHA Standards
In standard 29 CFR 1926.56(a), OSHA lists the minimum amount of light for operating zones encountered in the construction industry. For warehouses and similar indoor spaces, this standard requires illumination of at least 5 foot-candles. In mechanical shops, electrical equipment rooms, and other indoor spaces that host exacting manual work, OSHA mandates a light intensity of 10 foot-candles.
According to OSHA standard 29 CFR 1910.178(h)(2), forklift operating areas must be lit with at least 2 foot-candles; in darker spaces, lift trucks will have to use an auxiliary light source, such as headlights.
To learn about lighting requirements for other industrial settings, the OSHA standards recommend the American National Standard A11.1-1965, R1970, Practice for Industrial Lighting. The American National Standards Institute also provides useful information about workplace lighting at their website.
Armed with your trusty light meter and these hard numbers, you can easily ensure that your workplace is bright enough to keep your staff safe and productive. Plus, you’ll be certain that your facility is compliant with OSHA and ANSI standards.
“Discover Lighting.” IES. Illuminating Engineering Society, n.d. Web. 30 Sept. 2015.
“Illumination - 1926.56(a)” OSHA. Occupational Safety & Health Administration, United States Department of Labor, n.d. Web. 30 Sept. 2015.
“The NIST Reference on Constants, Units, and Uncertainty: Unit of Luminous Intensity (Candela).” NIST. National Institute of Standards and Technology, United States Department of Commerce, n.d. Web. 30 Sept. 2015.
“Powered Industrial Trucks - 1910.178.” OSHA. Occupational Safety & Health Administration, United States Department of Labor, 2006. Web. 30 Sept. 2015.