I’m always amazed at how much geometry is involved in lighting a set.  Two simple rules will help clarify the way you think about what you’re doing.  Don’t be fooled by their simplicity…they’re based on the laws of physics.

            The closer you get to a light source, the greater its intensity.

            The further away you get, the less its intensity.

            It seems obvious because it is.  It’s also the basis of the Inverse Square Law.  Look it up for further explanation.  Once you play around with it for a bit, you’ll begin to understand why we use nets, scrims, dimmers and all manner of light attenuating equipment to control the volume of what’s reaching our subject.


8 thoughts on “STUDENT QUICK TIP #18”

  1. From my observations, soft sources such as KinoFlo do not adhere to the Inverse Square Law which is used to define “Point Sources” — Close but not accurate. Moving a soft source 2 feet does not decrease the amount of light hitting a surface by 1/4. Comments?

  2. Gee, Greg, I don’t know about that. I’ll have to ask a physicist! 😉

  3. Instead of a physicist, pull out your Spectra with a flat disc and experiment!

  4. The inverse square law applies to ALL light sources. 50 years of moving and arranging every lighting unit imaginable has proven this to me, my Gaffers, Key Grips and our crews.

  5. A student asked me what light beam diameter he needed to fill a window of a certain size — I told him it was the diagonal measurement of the window which could be calculated using the Pythagorean Theorem (which is grade-school geometry…) Cinematography doesn’t involve much use of advanced math (unless you really want to) but it does require you can deal with calculating ratios, percentages, etc.

  6. David – I was a terrible math student growing up, but I’m amazed at how quickly and accurately I can calculate the various numeric challenges we face on a daily basis! My assistant once observed that I do it so well because it’s important to me…

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