What is a foot candle? How do you find out how many lighting foot candles you need at your facility? As lighting professionals, foot candles are our go-to unit of measure to calculate light levels. The word foot candle dates back to when candles were the main light source available. Read on to learn what are foot candles and how to measure foot candles!
A foot candle is a measurement of light intensity or illuminance and equals 10.76 lumens or one lux per square foot. A lumen is a unit of luminous flux or all of the visible light emitted from a uniform point source. If you were to set a candle or light bulb a foot away from a wall and draw a one-foot square on the wall, the amount of light filling up the square equals one lumen. The more lumens, the brighter the space and the higher the lighting level.
Lux measures luminous intensity and perceived light output just like a foot candle, but is in the International System of Units (SI), which is the modern form of the metric system.
Lumens and candela both measure light output as perceived by the human eye. Candela was once known as “candlepower,” which is now considered outdated. Candela measures the brightness of light output in a particular direction, while lumens measure how bright a light source (or candle as it once was) is in terms of light given off in all directions or the spread of the light.
To better illustrate this, imagine your employees’ workspaces. If they perform intricate and detailed work you would want to concern yourself with the candela values. On the other hand, hallways and conference rooms need more illumination across wider areas and in these types of cases you should concentrate on the lumens values.
One foot candle of light equals 10.76 lumens per square foot.
There is 10.76 lux in 1 foot candle.
The scientific term for foot candle measurements is “photometry,” which is the science of measuring visible light in terms of how it is perceived by the human eye.
Foot candle units are difficult to measure and it is best to get the help of a lighting company to help you get an accurate measurement through the use of tools like light meters. Light meters will display their readings in foot candles or lux.
Some lighting manufacturers will list the lumen count of their products, but even then when it comes to the actual application of the light in the real world the lumen light measurement may be off.
Our auditors will use a light meter (also called a lux meter or illuminance meter) to obtain an accurate foot candle measurement when they visit your facility. We use light meters at numerous points in your spaces to determine any specific dark spots and develop an average foot candle reading for each area.
There are two types of light meters: incident or reflected. Incident light meters measure the light illuminating the subject, while reflected light meters measure the light that is reflecting from the subject.
In addition to light meters, in the case of new light fixture installations or lighting retrofits, photometric software can be used to calculate proper fixture spacing, lumen output, and use of proper lenses or distribution patterns.
As mentioned above, the best way to obtain an accurate foot candle measurement unit is through the use of a light meter. There is no practical physical way to calculate foot candles, but you can find out how bright an area is by figuring out the lumen equivalent since lighting products in the U.S. include brightness levels measured in lumens on their labels. Remember, a foot candle is equal to 10.76 lumens.
Here are some quick formulas you can use if you need to figure out other measurements related to foot candles.
Foot candle to lumen/lumens from foot candles: Foot candles X 10.76 (for example, 4 foot candles is equal to 43.04 lumens)
Lumen to foot candle: Lumens ÷ 10.76
Lux to foot candles: Lux ÷ 10.76
Foot candles to lux: Foot candles X 10.76 (for example, 30 foot candles to lux would be 322.917 lux)
Watts from foot candles: Lumens X .001496 (for example 6 foot candles is equivalent to 0.0966 watts using the above formula to calculate 6 foot candles is equal to 64.56 lumens)
Watts to foot candles: Watts X 634527.76
Note: Watts is measured in watt/square centimeter (W/cm2)
By now we know a footcandle is equal to 10.76 lumens. To find out how bright 10 foot candles are we need to figure out the lumens equivalent of 10 foot candles. To do that you will need to multiply the square footage of the room or area of the building you are measuring by 10.76 foot candles to get your lumens equivalent. For example, if you have a 100-square-foot room, it would be as bright as 1,076 lumens.
It depends on the location and what the space is used for. For perspective, generally, you would see covered parking garage light levels in the 2-10 foot candle range, a gym 30-100 foot candles, and an office or chemical lab would have light levels in the 40 or more foot candle range.
The Illuminating Engineering Society of North America (IES) does not issue foot candle requirements but has a set of standard guidelines for particular applications when it comes to safety and adequate illumination levels. The IES cannot require a business to follow its guidelines and they should be considered recommendations. The IES guidelines are highly researched and considered the gold standard in the lighting industry. The IES’ recommendations should be followed by businesses that want to keep their employees safe and productive.
The guidelines are outlined in the IES’ “The Lighting Handbook, 10th edition.” According to the IES lighting handbook recommended light levels, for industrial lighting as it applies to cold storage or warehouse space, it is suggested to maintain an average of 20-foot candles in the area. The same goes for an open warehouse or a warehouse with aisles. When it comes to office spaces, an open office or private office area should have a light level average of 40-foot candles. According to the handbook, adequate lighting levels for a classroom is also 40. An automotive showroom or service area is ideally lit with 50 foot candles of light.
When it comes to recommended light levels for manufacturing, it will depend on if it’s assembly or component manufacturing. For simple, large item assembly manufacturing the suggested light level is 30 average maintained foot candles. For difficult, fine assembly manufacturing the suggested light level is 100 maintained foot candles. When it comes to large component manufacturing the suggested light level is 30 maintained foot candles, while the suggestion for medium component manufacturing is 50 maintained foot candles.
To further enhance the safety of your facility, the Occupational Safety and Health Administration (OSHA) provides lighting standards for safety. To learn more about those, please read this blog article.
Most major corporations set lighting standards using the IES guidelines and if needed adjust those levels to suit their specific operations. WattLogic’s Lighting Reference Guide is a free resource you can use to see what the suggested light levels are for all types of facilities.
If you’re looking to meet recommended lighting levels in your facility the most cost-effective way to do it is through LED light. Upgrading to LED lighting technology is one of the best ways to reduce energy consumption and save money. On top of that, you’ll see an increase in productivity, quality, and safety. An added bonus is you will experience a brighter and more welcoming facility.
If you have a specific question about suggested light levels within your business please contact us at (800) 834-8737 and one of our team members would be glad to assist you.
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