A foot-candle is a measurement of light intensity or illuminance, and it equals 10.76 lumens or one lux per square foot. If you 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. To find out how much lighting you need at your facility, lighting professionals use foot candles as their go-to unit of measure to calculate light levels
Lux is the modern form of the metric system and measures the luminous intensity and perceived light output just like a foot candle. The difference between lumens and candela is that candela measures the brightness of light output in a particular direction, while lumens measure how bright a light source is in terms of light given off in all directions or the spread of the light.
To measure foot candles, lighting professionals use tools like light meters that display readings in foot candles or lux. They may also use photometric software to calculate proper fixture spacing, lumen output, and the use of proper lenses or distribution patterns. When it comes to calculating foot candles, there is no practical physical way to do it, but you can find out how bright an area is by figuring out the lumen equivalent. For example, 10-foot candles are equal to 107.6 lumens in a 10-square-foot area.
The amount of foot-candles needed depends on the location and use of the space. Covered parking garage light levels are generally in the 2-10-foot candle range, while a gym requires 30-100 foot candles, and an office or chemical lab needs 40 or more foot candles.
What are some common light sources and their foot candle outputs?
Different light sources produce different levels of foot candles. Here are some common light sources and their approximate foot candle outputs:
- A 60-watt incandescent bulb produces about 15-foot candles at a distance of 8 feet.
- A 100-watt incandescent bulb produces about 25-foot candles at a distance of 8 feet.
- A 23-watt compact fluorescent bulb produces about 15-foot candles at a distance of 8 feet.
- A 15-watt LED bulb produces about 7-foot candles at a distance of 8 feet.
- A 40-watt fluorescent tube produces about 30-foot candles at a distance of 8 feet.
It’s important to note that the foot candle output of a light source can vary based on factors such as the type of fixture, the angle of the light, and the distance from the light source.
In conclusion, understanding foot candles is important for ensuring that your space is properly illuminated. By knowing the difference between foot candles and Lux, lumens, and candela, and how to measure and calculate foot candles, you can make informed decisions about the lighting in your facility. Also is always good to consider a photometric plan from professional lighting designer prior installing any fixtures. Remember, the number of foot-candles you need will depend on the location and use of the space, so it’s always best to consult with a lighting professional to ensure you are getting the right amount of light for your needs.