YongLee Posted January 9, 2008 Share Posted January 9, 2008 i know the"the inverse sqare law " of light ,but i think it is apply to spot light only, for large surface light , it is not right. who can tell me how the"the inverse sqare law " of light to use in lighting film sence? thanks! Link to comment Share on other sites More sharing options...
Premium Member Michael Nash Posted January 9, 2008 Premium Member Share Posted January 9, 2008 The inverse square law applies to a point source only. The larger the source (in surface area), the less the light falls off with distance. How much less depends on the size of the source, relative to the distance. Link to comment Share on other sites More sharing options...
Matthew Parnell Posted January 9, 2008 Share Posted January 9, 2008 The maths that specifically applies to the falloff of a diffused source has been discussed in the past, it is rather complex and confusing. just do a quick search of the forums. Link to comment Share on other sites More sharing options...
Premium Member John Sprung Posted January 9, 2008 Premium Member Share Posted January 9, 2008 The maths that specifically applies to the falloff of a diffused source has been discussed in the past, it is rather complex and confusing. ... Nah, all you gotta do is treat every point on the large surface as a point source, and just do an integral in two variables. Piece o'cake. ;-) -- J.S. Link to comment Share on other sites More sharing options...
Steve London Posted January 9, 2008 Share Posted January 9, 2008 Besides large sources the inverse square law doesn't apply to collimated sources either, where a reflector and perhaps lenses direct light (more or less) in one direction. So, while our movie lights rarley rigorously obey the law it's a useful first approximation in practical circumstances, though. Link to comment Share on other sites More sharing options...
Steve London Posted January 9, 2008 Share Posted January 9, 2008 Piece o'cake. ;-) -- J.S. I got As in more than a year of Calculus and you took the words right out of my mouth. :lol: Trivial. I'm a little busy though, so I'll let you post the equations and get the credit. (Hope the humor is obvious, John.) Link to comment Share on other sites More sharing options...
YongLee Posted January 11, 2008 Author Share Posted January 11, 2008 thanks , everybody! : :rolleyes: Link to comment Share on other sites More sharing options...
Premium Member Tim O'Connor Posted January 12, 2008 Premium Member Share Posted January 12, 2008 The inverse square law applies to a point source only. The larger the source (in surface area), the less the light falls off with distance. How much less depends on the size of the source, relative to the distance. I know this and yet...everything is relative. The inverse square law doesn't apply to the largest soft light on Earth and yet the largest point source in the world (to us anyway) is the sun, which is bigger than any soft light or frame of diffusion that I've seen. I'll never forget shooting for NASA (footage still classified) when we got so close in the rocket to the sun that the light coming in the window went from casting shadows to being the biggest wrap around soft light. Link to comment Share on other sites More sharing options...
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