What is the difference between footcandles and lux?
There is no difference between foot candles and lux in respect of what they measure.
In the same way that feet, inches and metres both measure length, foot-candles and lux both measure the illuminance (the amount of light) that falls onto a surface.
The footcandle is an ‘imperial measurement’, while lux is a metric (or SI) measurement.
What is the difference between the two figures?
Footcandles are more or less ten times the equivalent lux measurement, which comes from the way that the light is measured.
Take a beam of light and measure its intensity at one foot away from the source and that will give you the foot candle reading. Take the same beam of light and measure it from one metre away from the source and that will give you the lux measurement.
One footcandle equals 10.764 lux.
One lux equals 0.09 ftc.
How to Convert Foot-Candles to Lux?
Scientists measure the brightness of a light source in units of candles or, when using the metric system, in candelas. The amount of illumination — or illuminance — a surface receives depends on the distance from the light source and the intensity of the light source.
Illuminance is measured in either foot-candles or the metric system units of lux. You can readily change foot-candles to lux by using a simple numerical conversion factor.
Enter the numerical value of illuminance, in units of foot-candles, into the calculator. For example, if your illuminance value is 22 foot-candles, you would enter 22.
Multiply the value which you just entered by 10.76. This is the conversion factor between foot-candles and lux. In the above example, you would calculate 22 x 10.76 = 237.
Report the result of the previous calculation as the illuminance in units of lux. You have now converted the original value of illuminance in units of foot-candles to units of lux. The example would therefore be reported as 237 lux.