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Inverse Square Law

let's talk about the inverse square law and I remember in college in college I studied photography business in political science it's weird that started share that always you um but I remember when my teacher was explaining the inverse square law and drew all the diagrams and all the numbers and I was like okay and later on when I realized he was saying it's just something I like new intrinsically and it just freaked me out because of all the diagrams and numbers okay this is a story this is real it is true in college in my first studio class okay so I was a perfectionist and I got like a head for point owned everything which for people too I don't have that system it's basically like a you know one hundred percent all the way across and one of my first studio classes I got like a b minus because I've refused to drive draw the stupid diagrams and like do the calculations for the inverse square law and so I got doc's because I didn't do the documentation because it just like overwhelmed...

me that I had to like actually draw out on grids where things were placed and how the light was dropping off basically so we're not going to do that because I am traumatized by it mildly traumatized is not that so I am going tio say the technical terms so if it bothers you just two now and then we'll get to like why you actually care afterwards all right so who cares what does it mean to me all right so the law is when you double the distance from the light the power of that light quarters so what that would mean can I brought sydney and stephen please all right so I'm just standing here and I gotta make sure they're all on screen okay yeah what can I send you here sidney right perfect so if I am the light okay right here if on signa jane the light is f eight okay steven is about double the distance from me in the light so it's not f eight five six on him it's actually essay for o on him it's not step by step it's not like it cuts down one stop each time it doubles it actually quarters the power so that's more or less kind of what that means it's not like if I take a picture of her she he's going to be half assed greatest her he's gonna be a quarter as bright as her so that's what the inverse square law means I'm still not to the easy part yet this is still like the semi technical part um let me see I might still stand you out here okay so do you want to just two step that way just for a second sorry so that's the diagram of it which basically means if you see it's the bucket of water doesn't exactly translate but if you were throwing that bucket of water the water just spreads everywhere and it gets weaker very quickly so by the time we're far away there's no light there's no water but what it what you're looking at is double the distance the power doesn't cut in half a quarters okay so let's see what it really means ok so what it really means is light drops off exponentially it's not like a step by step thing it's very very drastic okay so I am going to demo in a second but here's for the people that didn't want to listen to the numbers and all that stuff what is it what does it actually mean and how does it come into practice when you're shooting on location the two important things it means the very first one is if you bring your like closer to your subject there'll be a faster fall off so I'm gonna show you what that means in a second and then the other one is if you move your light away just in general you're moving away from your subject gets dimmer if you move it closer it gets brighter but it's exponential it just it's it's very quick in the amount that it gets dimmer or brighter all right so I'm going to do the example for the bring the light closer example all right so since when have you stand it here all right so in this example how we have it right now they're about double the distance right let's just say it's two feet to her another twelve it's a little off take one half step back we'll say it's about two feet of her and I'm just you know studio um two feet to herd to feed to him okay let's say that I want to go ahead and make them approximately the same brightness and I'm the light in order to make them approximately the same brightness I have to move really far away now if I am going to the double the distance from sydney is way far away he's actually relatively close so the light far off is not that significant they're pretty much similar distance based on how far I backed up if I wanted to go ahead and quarter the power it would be out of this room so right there they're going to be a lot more similarly let similar exposure but if I'm the light and I want steven to be very very dark and city to be very very bright the like to fall off drastically I move way way way way way up right here or as close as you can get your light because now the distance between my light is maybe a half a foot so now it goes quarter power quarter power quarter power and now he's very very dark that's all the inverse square law really means in that sense it's the fundamentals of it if you want the light falls to look drastic you bring it really close and then whatever is in the background will be darker if I want them to be s'more similarly lit I back my light way way up and I'll be more similar the letter so there's more to it but I want to make internet if that did make sense feel free how about you made it okay so just let us know in the chat room if you are getting it I know that we've got green katie who says thank you for breaking this down to this basic level I've been shooting professionally for a few years but really appreciate your explanations especially of problems I've run into and haven't really figured out yet you're super your confidence is making me feel confident excellent so thank you for sharing that green katie so stephen when have you say sydney where you step off for a second so okay so that's one example of how it plays a role but I was just comparing to people how it probably makes a big difference on location is when you want to separate your studio strobe so that it's not lighting the environment as well you want them separated or you want them the same you want your students drug also light your environment so for example if I want steven and that wall to both be illuminated by my strobe both be hit by the strobe if I back up really really far they're relatively close together if I backed that light up so now the light is definitely going to hit him and then we dimmer behind him but it'll still definitely reach the wall but if I want that wall tickle really black really dark I bring my light up really really close and then the fallis is extremely drastic and I can get that to be much darker so of course we're talking about location lighting this is the same in the studio if you can't get your background to be totally black if you bring your light closer it'll make a big difference you brought the light closer wouldn't like literally blow him out I mean we just like be overexposed so as you bring it closer let's say that when my light was here it's a fate okay soon as I move in let's say I get to the point where it's like f sixteen like it just got a gut significantly brighter I have to compensate with my exposure in my camera so get it got really bright but instead of keeping my camera that fate now I compensate and we'll shoot appropriately at whatever he's lit at f sixteen of thirty two phelan's does that so you just have to make a change in your camera at that point um and then also you have the ability as well you bring your light weigh in and weeks we talk about this a bit but I bring it way and it's way too bright for what I wanted to do in my scene you can turn it down you can turn the power of the light down if it's not already is lois power and it'll still have that light fall off effect like the way the light behaves is the same it's just at lower values it's just like not as bright it's doing exact same thing so lindsay just to clarify for joanne la above she says does the power of the light stay the same technically the power stays the same but the amount of light that actually hits them exactly what lower so exactly it's as though you move the light closer and turn the power way down yes oh so for example there's two ways you can do this as I move the light in we'll do the bucket of water thing okay so the bucket of water at him it spreads out it lights him I got the same amount of water but he's a lot more soaked if I'm right here basically so that the amount of lights the same and then if I want him to be the same level of soaked as it was here but I just moved in I got to dump out some water first you know I got to make it less light and hit him so it'll be the same so it is about amount of light it seems like there's more like when you move it closer because of that whole fall off thing so this is the whole practical use of the inverse square law thie other reason becomes important can I borrow sydney again if she's here perfect I'll gonna break all this down billy thing first thing other thing it's important and I see this a lot is for groups this is where one gets people get really messed up on location because let's say I'm going to stand you guys kind of side by side on then take week three steps apart all right so let's say that there's a bunch of people but between them and you're lighting a group and you've got your light over here well stevens about double the distance from that light of sydney which means he's gonna have a quarter of the power of light which means it's in me two stops darker than she is so when lighting groups it becomes a little bit more challenging and so there's some things and I'll talk a little bit about letting groups but let's say I mean on the light on lighting the group here it's probably better for me to flat light a little they move around to the front so roughly they're the same distance versus if I take that light far off to the side or if now I'm lighting her and he's a little dim you might put one light here and then another light over here and so then the late in the middle of everyone's getting kind of evenly illuminated so that's a trick when lighting groups I think yeah again and just because this is ah tricky thing I want to make sure that everyone gets it's the questions after that they want end west where if you have will you have the same follow if effect if you have a narrow beam like if you've snu did the light compared to if you use a big modifier okay so the the answer is yes and no the math is the same but when you have more focused light you've intent intensified in one direction so the numbers are the same but the way it works is a little bit different if what's a good unlike looking for my bucket and love like a good focus here if I have a spotlight on steven okay and it's hitting his face here the light's still going to fall off behind him but it's going to be if I take the huge bucket right and it spreads out everywhere it stays in this church directory more the late back is more dramatic than it is across like the distance makes more of an effect versus more of the spread of the light so I if you want the light to stay focused longer it does help to have a more focused beam but it's still going to have same life off so I would say for simples city's sake the math is still the same like even if I have a focus light if she's up here and bring you this way even if I have that focused beam he'll still be a fuse double that is since he's still going to be quarter of the power that's the easy way of explaining that makes sense well to say the answer is yes to make it easy okay all right so next one um now stephen you can step out we're rotating okay and sit back just a little bit all right so then I just gave you that light fall off thing the other important one for our purposes is you move the light closer it gets brighter you move the light away it gets dimmer if you have that same bucket of water okay we're talking about that here's why it makes a difference to you we will definitely run into issues where our studio strobes we can't quite get them bright enough or we can't quite get them dim enough you will definitely run into this on location where you're shooting you're trying to overpower the sun and it's just not bright enough to do it well since we know if we move the light closer we're like as we move the light closer here it will quadruple the power we're going the office it's way instead of quartering we're going to quadruple it so if I'm shooting about trying to overpower the sun the light's not right enough I know that if I can bring the light half that distance right now have increased the power by two stops which is a big difference if you're trying to overpower the sun okay and then the same thing is sometimes you're in like really like I've had this situation recently actually the very end of the day I show this I was in a really dim lit library really dim lit and I'm shooting wide open at like one point four and I was having my subjects hold really still um and it was bringing up the exposure but everything was really really dark and so I needed that one point four toe let in light okay my studio strobe with the five hundred watts second strove if you guys have tried five hundred watt seconds in the studio to be able to turn it down far enough to get one point four isn't easy the gate's not easy to get that damn there are tricks around it but one of the things if it was still just too bright too bright too bright I've got rid of all the tricks in my bag I couldn't get any dimmer if I double the distance a quart of the power I just dropped it down two stops so those air this is why these things become practical walls and groups if you want fast light fall off if you need to make your light dimmer or brighter so you're all done first second those are the most important things that you'll need to know about how light behaves for taking it on location and trying to give this all to work