# Is the Inverse Square Lux calculation accurate for flashlights?



## Blindasabat (Jul 12, 2010)

The inverse square law appears to assume that the radiation is a point source. Since flashlights use a collimating optic of some sort that projects light off of a surface of a definite area, I surmise that calculating lux at one distance based on lux measured at another distance may be subject to some inaccuracy. The point source may be a virtual point some distance behind the flashlight. It is likely difficult to determine that point. 
The extreme example of this is a laser. 
Has anyone taken lux readings of the same light at several distances to see if they confirm the inverse square law is accurate?


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## Bullzeyebill (Jul 13, 2010)

There has been discussion regarding this topic recently, and mudman cj did this thread last year, a pretty good study.

Bill


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## Blindasabat (Jul 13, 2010)

I figured the discussion would have been in this sub-forum so I searched here for it. My bad. Thanks for the link. It is exactly what I was looking for.


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