Converting foot candles to lumens
In the lighting industry most people understand what a foot candle is, which is a measurement of light intensity.
In the LED we prefer a more useful unit of measurement of Lumens and Wattage. It becomes much easier to access lighting from foot candles to lumens once you know a few calculations.
Although, most digital light meters measure in lumens (which makes it very easy) some don’t. The following simple steps will help you calculate from foot candles to lumens.
First Step:Light Intensity
The first thing that you need to do is use your light meter to measure the number of foot-candles that there are hitting the subject, which could be a floor or table. Once you have this number, you can then use it to convert it into Lumens or Watts depending on what you want to do. For the case of this example, we will base our calculations on a measurement of 100 foot-candles.
Second Step: Converting to Lumens
One foot-candle is equal to 10.76 Lumens. This means that you need to take your foot-candles measurement and multiply it by 10.76. Using our measurement of 50 foot-candles, we get the following equation: 100 x 10.76. By working out this calculation, you will be able to get 1076 lumens. A lumen is the same as Lux and is what many modern light meters will calculate their measurement in.
Third Step: Converting into Watts
The next thing that you can do is to calculate the number of watts. This is very easy to do once you have converted into watts. One lumen is equal to 0.001496 watts. This means that you simply need to take your answer to step 2 and multiply it by 0.001496. In our example, 538 x 0.001496 equals 1.61 watts per square meter. I always write the calculations down since it’s easy to forget when numbers and calculations are being used.
Understanding how all the numbers come into play using these calculations makes it easy to do you own measurements in the field.
Remember to work out Lumens or Lux use the following Equation: Lumens = Foot-Candles x 10.76
Also, to work out the Watts use the following equations: Watts = Lumens x 0.001496
Additionally, you can also calculate the number of watts directly from the foot-candles by combining both equations and using the following: Watts = Foot Candles x 0.01609696 This is because 10.76 x 0.001496 = 0.01609696).
If you can remember these numbers you’ll even be able to do calculations in the field without too much effort.