What is a foot-candle and how do you find out how many 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. A foot-candle is a measurement of light intensity and equals one lumen one square foot or about 10 lux. A lumen is the amount of visible light given off by a source. If you were to set a candle 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.
We use light meters to measure the amount of foot-candles at numerous points in your spaces to determine any specific dark spots and develop an average foot-candle value for each space. Additionally, for new installations or retrofits, photometric software can be used to calculate proper fixture spacing, lumen outputs, and use of proper lenses or distribution patterns.
How do you determine how many you need? It depends on the location and what the space is used for. For example, you would generally 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 has a set of standard guidelines for particular applications when it comes to safety and adequate illumination. For example, according to the IES’ The Lighting Handbook, 10th edition, for a 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. A classroom should also have 40. An automotive showroom or service area is ideally lit with a 50 maintained foot-candle average.
Most major corporations set lighting standards using the IES’ standards as a guideline and if needed adjust those levels to suit their specific operations. Click on this link to download a reference guide for suggested light levels in even more facility types than mentioned in the previous examples: U.S. Energy Recovery Lighting Reference Guide.
If you have a specific question about suggested light levels within your business please give us a call at (800) 834-8737 and one of our team members would be glad to assist you. Thanks for watching!