Skip to main content

Lighting 101

Lesson 21 of 65

Inverse Square Law in Practice

SLR Lounge, Pye Jirsa

Lighting 101

SLR Lounge, Pye Jirsa

Starting under


Get access to this class +2000 more taught by the world's top experts

  • 24/7 access via desktop, mobile, or TV
  • New classes added every month
  • Download lessons for offline viewing
  • Exclusive content for subscribers

Lesson Info

21. Inverse Square Law in Practice


  Class Trailer
Now Playing
1 Chapter 1 Introduction Duration:01:26
2 Why Just One On-Camera Flash Duration:04:22
3 5 Reasons to Use Flash Duration:10:37
4 Common Flash Myths Duration:06:51
6 Chapter 2 Introduction Duration:01:36
9 Flash vs. Ambient Demo Duration:06:42
13 Understanding Flash Duration Duration:08:37
14 Chapter 3 Introduction Duration:01:34
15 5 Common Key Light Patterns Duration:08:38
18 3 Primary Subject Patterns Duration:05:27
19 Light Qualities Duration:09:56
20 The Inverse Square Law Duration:07:50
21 Inverse Square Law in Practice Duration:08:21
22 Corrective White Balance Duration:10:02
23 Creative White Balance Duration:05:47
24 Chapter 4 Introduction Duration:01:58
25 On Board vs. Hot Shoe Flash Duration:05:57
27 TTL vs. Manual Control Duration:08:12
28 TTL vs. Manual Recycle Times Duration:04:43
29 Flash Power & Zoom Duration:09:18
30 HHS vs. ND Filters Duration:12:29
31 FCS vs. RCS Duration:07:11
32 Chapter 5 Introduction Duration:01:38
34 Bare Bulbing Done Right Duration:11:42
35 Grid Snoot + Direct Flash Duration:06:43
36 Mini Beauty + Direct Flash Duration:06:08
37 Ring + Direct Flash Duration:07:52
38 Understanding Modifiers Duration:09:24
39 Direct Flash + Shutter Flash Duration:09:07
40 Chapter 6 Introduction Duration:01:55
42 Silver Bounce Duration:14:27
43 More Light Silver Duration:11:02
44 Soft White Bounce Duration:15:41
45 Overhead Bounce Duration:11:39
46 Overhead Bounce + Fill Duration:09:42
47 Event Bounce Duration:12:42
48 Chapter 7 Introduction Duration:01:38
49 Natural vs. Dramatic Light Duration:17:43
53 Chapter 8 Introduction Duration:00:43
54 Case Study 1 - Dramatic Sunset Duration:09:45
55 Case Study 2 - Desert Sunset Duration:10:04
57 Case Study 4 - Family Portrait Duration:08:21
59 Case Study 6 - Working Angles Duration:07:22
61 Case Study 8 - Less is More Duration:07:16
62 The Good Karma Jar Duration:01:41
63 Favorite Feature Flashes Duration:05:52
64 Favorite Manual Flashes Duration:21:35

Lesson Info

Inverse Square Law in Practice

It isn't my favorite slide inverse square pie man kind of like pac man but I'm pie. You get it? Okay, you will get in just a second. This lovely rhea world demonstration or kind of early my world demonstration gives you an example of inverse square law in breakfast. This isn't really good practice, but it does show you an example. We have the light placed over here on the left side. Okay, these are all different frames. And basically here, where one foot two feet, three feet, four feet five feet six feet away from the life let's say that at one foot we're getting one hundred percent of the desired light that we want when we set away to two feet, you're gonna notice that I'm far darker then this shot right here this shot I mean is virtually on the edge of being blown out. This shot is like one quarter, not like one quarter that is one quarter of the intensity of this shot. As we step away, you can see me getting darker and darker and darker. Now the interesting to note is that the diffe...

rence mean one foot and let's say three feet is extremely dramatic in brightness, okay that's a huge difference there, but there's protein, five feet and even seven feet is a very small difference it's much smaller then that initial different. So what we're essentially learning is that the further that we get from the light source, the light is now falling off at a much slower pace than up close to that light source. Okay, so we've seen it in pies world let's see another ria world demonstration featuring creepy joseph. Okay, so what are we doing here? Well, inverse square line practice and granted, he wouldn't take a crappy photo like this in practice. This is just because I want to show you all a creepy, crappy photo, but in this shot right here, what we've done is we basically placed the flash right to the left side of olivia's face. Joe's distance is roughly one foot from olivia olivia's distances roughly one foot from the flash and this makes joe's distance for the last double what olivia's is. So if you look at olivia she's nice, bright and properly exposed, if you'll get joe he's about three four stops underexposed ok, especially when you start getting to the other side of his face, he gets even darker. Now. Joe happened to kind of creep into her a little bit too close on this one, but this is where the flash is basically four feet from the model. Now what we've done here is, all we're doing is we're adjusting up the flash power every time we take a step away, we have to adjust the flash power up to compensate, because now the distance of the flash to the subjects is much further. But look in this one, joe was basically double the distance of olivia from that flash. Where is on this side? Jos now on ly one foot further than olivia so olivia's four feet from the flash and joe is five feet, so you'll notice that the fall off is much less dramatic. Joe is actually much more similar and exposure to olivia. Here we move the flash eight feet away, we powered the flash up higher a little bit more and again. Joe is a creepy six inches away from olivia's face and she's enjoying it, she's loving this whole thing, by the way. But here joe's, roughly nine feet from the flash and olivia's roughly eight feet so you can see the exposure's equal out. We're having to go more flash power, but the further we get from the light source, basically the further the group is in, the more similar their relative distances so now olivia's only eight feet joe's nine feet and we get roughly the same light. So when we're lighting a large group let's say the group is ten feet wide, I might need the flash maybe twenty, thirty feet away, depending again on the angle of that light from the group to be able to get everybody roughly the same brightness and there's other techniques too this too that will cover in lighting to one and three when we take the camera won't take the flash off the camera now before we conclude this crazy crap tastic lot has been made way too complex the inverse square law let me give you four simple takeaways number one the inverse square law still applies to individuals, meaning if I'm shooting a lovely model, whether it be a guy or a girl let's assume that it's olivia in this instance in this shot, I've placed that light so close to olivia's head that if I'm shooting olivia full length, her head is gonna be so much brighter from the rest of your body and you can actually see that the flash is right here and you can even see by the time it reaches her chest. I'm only getting twenty thirty percent of the amount of light as I was on her face, so if I place a light modifier super close to somebody it's going to still have the same effect, even if I'm just shooting them individually versus as a group remember, if I want equal light across an entire part of the body, then that light needs to be roughly equal distance from the entire body, from head to toe. Okay, number two, the more people you have in a shot? Well, in general, it means the more distance you want tohave, so the larger the group simply move the light away a bit further to get even lie on everybody, and that means you're going to need to power up the light remember that you're losing more light than you think you are every time you double the distance, you quarter the flash power that you have remaining okay, so doubling the distance means twenty five percent the power number three the basic rule of thumb when you're trying to light a group of individuals, let's say, a group of ten people is is each ten person is each person is each ten person kind of english that is, each person in this ten person group are they each roughly the same distance from my light source, not my life sources fifteen feet, twenty feet away, then a difference of likes a one a two feet between, you know that relative distance isn't really going to make too big of a difference, but if we're talking about twenty feet from the light on one side versus ten feet from the light on the other side yes, you're gonna get twenty five per cent of light on that side and you get one hundred percent of your life on the other side. Okay, so just remember is everybody roughly the same distance from the life source number four is the more dramatic the angle of the flash, the mohr distance that you need to have the same relative distance and everyone in the group and here's what that means all this means is it my flash is directly on top of my camera, which, again, this really depends on what tools you have with you and what kind of you know what you have blisters sam using direct flash on a group of fifteen people from standing ten feet away than my distance to all fifteen people is roughly the same. It might differ by legs say six inches to a foot or so as that direct flashes on my camera and it goes out to each person in the group very little difference. I'll get roughly the same out of brightness on every person from that angle, but as soon as I take that flash off the camera and I'm let's say I don't even need to remove the flash on the camera could be bouncing from a reflector or whatever it is assumed I moved the primary light source away from the camera it's becoming more dramatic, right? We're getting more shadows now that light is going to be favoring one side of the group far more dramatically than the other side. So assuming that lights at an angle, the group that's on this side is now going to be probably, well, far closer, maybe ten feet from the flash. Where's, the group on this side is going to be twenty feet from the flash, so the more dramatic, the angle of the flash to the group, the more distance you need, the greater the distance. You gotta pull back even further to get an equal light from right to left. So that's why, when doing a group shot a lot of times, they'll place lights on both side. They'll cross lighter so everybody has even light, or they simply shoot group shot with an individual light in each portion, the group and that's, something that we might do in lighting to one and lighting three also advanced techniques for shooting large groups with off camera flash. All right, so at this point, I know all of you have absolutely mastered the inverse square law, and you understand, you can explain it to anybody who asks, and you'll be like, look, did this was totally so much more simple than everybody else explains it out to be here, this that's, what I want you to do. I want to stay with that. Same, like exact tone and accident. Everything like that. Let's, go the next video.

Class Description

Lighting 101 follows in Photography 101's footsteps. Photography 101 takes students up through Manual Mode mastery and provides a foundation in natural light techniques and modifications. Lighting 101 picks up by teaching all about flash and light modification. But, just like Photography 101, we want Lighting 101 to be the most accessible lighting course available. So we teach you everything about flash lighting, light modification, ambient to flash balance, lighting patterns, off-camera lighting and even multi-point off-camera light setups. But, what makes Lighting 101 truly special is that we do all of this with nothing but your on-camera hot shoe flash. Every image shown and created in this course was created with a DSLR and just a single on-camera hot shoe speed light. 

Graduate to the next level of exposure mastery with Lighting 201, Lighting 301, and Lighting 401 with Pye Jirsa.



The best class for understanding light and lighting there is bar none. Pye is an excellent teacher and the quality of the material provides for a rich and very informative experience. Pye breaks down the fundamentals in easy to digest packets and then elaborates as needed. If there is one class that you watch this is it! Worth purchasing and saving for future use. I would also HIGHLY recommend downloading the saving the PDF of slides that accompany the videos. Again, and can't say it enough, this is THE BEST video to lighting on Creative Live. A must watch for the novice and the expert.

Simon Metselaar

This is the best thing that happened to me since I've been into photography. What a lifesaver. Unfortunately I already payed for some courses that are not Pye, but Pye just nails it. Amazing, and kind of a life hack. Thanks again :)

George Gan was well worth your training. I have learned some key lighting techniques from this training. His voice and training is clear except for his attempt at making jokes and should hire a new script writer for your Jokes...ha ha ha ha. With that said, if you are not a professional in lighting, you do gain a lot going through this training from front to end. Remember this is lighting 101 so don't expect too want more technical and complexity, wait for Lighting 201, 301 or 401 ...