Foot candle is a traditional measure of light illumination, while candela is a more modern measure of light intensity at the light source.
One foot candle of light is the amount of light that a candle produces 1 foot away from the candle. According to the University of North Carolina at Chapel Hill, the modern way to measure illumination is in lux (lumens per square meter), and 1 foot candle equals 10.764 lux.
Candela is a measure of how much light a light source produces, measured at the light source, rather than how much light is on an object away from the light source.
Candela Technical Definition
According to the University of North Carolina at Chapel Hill, candela is the "luminous intensity of a light source producing single-frequency light at a frequency of 540 terahertz (THz) with a power of 1/683 watt per steradian, or 18.3988 milliwatts over a complete sphere centered at the light source."
TheLEDLight.com sums up foot candle vs. candela this way: candela is a rating of light output at the source and foot candles are a measurement of light at an illuminated object.
According to Spectra, a manufacturer of light meters, candelas are equal to the square of the distance multiplied by the number of foot candles. For example, if your light meter is 10 feet away from the light source with a reading of 10 foot candles, the number of candelas equals 10 feet squared (100) times 10, which is 1,000 candelas.
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