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6. Artificial light – Project 55, Light Intensity

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The object here was to make a graph, similar to P38 – which measured the intensity of daylight throughout the day – now using flash.

The inverse square law states that light falls off, inversely, with the square of the distance.

If you were to measure the intensity of a flash at perhaps 2 meters distance, then at say 4, 6, 8, 10 & 12 meters you would draw a graph similar to the one shown here.

As the distance (to the camera) doubles, so the intensity of the light from the flash unit halves, requiring the appropriate increase in aperture size, by a constant exposure setting. Basically the intensity of the light from the flash unit will fall off dramatically as the distance increases.

The reason why the power of the light diminishes so rapidly is not because it 'runs out of energy' but because it spreads and so a smaller and smaller proportion of the light hits the object. As you can see from the second diagram the beam of light fans out quite quickly and the object furthest from the light receives only a small proportion of the light, most of the beam misses the target.

A good analogy I read was to imagine the flash as a spatter gun (third image). The gun contains a small amount of paint, and shoots it at the scene. The further away the subject is from the flash, the less paint will get to the subject. If you double the distance from subject to flash, the amount of paint reaching the subject is just one quarter. This is because the paint is spread out over an area, which is related to the square of the distance.
29th Dec 2009, 14:57  


Dhamaka says:

must go through this when I have some time
HNY to you both

29th Dec 2009, 21:39

me says:


6th Jun 2013, 21:32

your dad says:


9th Mar 2015, 17:28

kaysoundafriartgallery2015 (olamoses25-at-yahoo-dot-com) says:

Creative and Lovely

16th Apr 2015, 22:18

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