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Inverse square law 

Date: 20120321 
Inverse square law

Light Source = Light source Intensity, I = Illumination h = Distance P1 = Flat Lux = Lux
Light exposure to the vertical plane of a point on the direction of illumination is equivalent to the brightness of the light source divided by the square of the distance to the plane, if we say that the distance h, to deduce the following formula:
For example: an exposure light source out of 100 cd candlelight, when the light source to the vertical plane at a distance of 3 meters, the plane illumination will be 100/32 = 11 lux lux; When the light source to the vertical plane of the distance of two public Feet, the plane illumination would be: 100/22 = 25lux lux.
This relationship is called the inverse square law, but directly to say, this only applies to point source; In general, the law of the light source to the most suitable for measuring the distance between points is greater than the maximum area of the light source for more than three times the length; to the other laboratory measurements of the data, the distance light source is required at least five to ten times the largest area long.
Brightness (I) and luminance (E) relationship  inverse square law
 

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