Peter Hurley - How to Understand the Inverse Square Law - Photo Lighting Explained

[@juleswrenches909]

Holy crap. It’s 2023 and I’ve just stumbled upon this tutorial. Learned SO much. Thank you.

[@alext9067]

Peter, extremely good explanation. Little fly in the ointment. Maybe I shouldn't say anything. I'll be cryptic. 6:31. See the wall behind your bud? You're at f2 (if I remember) something like that, and iso is 100. You take it from there. Again, super job.

[@karikaru]

In spite of the criticisms and potential technical fallacies, I found this demo to be very practical and helpful for just a general understanding of creating some basic effects with a light. Just now dipping my toes into the world of strobe photography and can't wait to experiment.

[@NiiloIsotalo]

This got me thinking how bright the sun actually is... Pretty crazy!

[@WOWStudiOsVideOs]

Do some research and it may actually awkwardly surprise you.

[@leonardrou]

Many watts of power per second.

[@yoyoz333]

its a fireball that is more than 100 times bigger than earth.

[@mushvisuals3064]

or its a lot closer than they say it is

[@rolobotoman]

here comes the flat sunners..

[@TinkerJD]

What Peter presents here is Hurley's Inverse Inverse Square Law. Hurley's visuals are broken by metering between each shot and shooting in a room that has reflective (diffuse) surfaces. To measure out the math of the Inverse Square Law and show it to us viewers visually, he should leave the settings on his camera set for proper exposure of the first shot and be shooting with a single source of light in a blacked out room . Moving the light back farther then causes an obvious light reduction (the inverse square law in question) and a sharpening of the subject's shadows. The farther the light source is from the subject, the more light your source has to produce to expose the subject properly. That light reduction effect is governed by the Inverse square law. The sun is really bright, and really far away, but despite Hurley's Inverse Inverse math the sun produces really sharp shadows. The shadows in question become sharper the farther the light source is from the subject matter and the closer the subject is to the shadowed surface. That's why your feet have sharper shadows than your head on a sunny day. Your head is closer to the light source and farther from the surface. Your feet are farther away from the light source and closer to the surface. The background wall "color trick" works, but you have to move your subject in close proximity to the light source and away from the wall to create diffuse shadows. If you move your light source away from the wall without moving the subject, your subject will cast harsher shadows even when being properly exposed. You can try this with a flashlight or your cell phone light right now. Shine your light on your hand while hovering it above your desk. The farther you hold your light from your hovering hand, the sharper the shadow on the desk becomes. If you bring your light toward your hovering hand, you'll see the shadows blur along their edges. This blurring shadow effect is opposite of what Hurley claims in the video. This is a really long comment. Thanks for reading it. This shadow softening falloff concept shouldn't have been mentioned in a video about the inverse square law, but I get the impression Hurley's trying to sensationalize his ideas about photography and he presented a falsity which will be confusing to many future photography hopefuls.

[@ryandinan]

You are completely correct about the effect of shadow sharpness/softness based on the light source distance. I think Peter was falsely attributing the various shadow effects on the male model to light falloff (inverse square law) when in fact it's being caused by the angle, size and shape of the incident light source. Since light falloff affects the intensity of the light - and because he was metering and adjusting his aperture between each shot as he moved the light - he was in effect, getting the about same amount of light in each shot. What WAS changing was the position and relative size of the light compared to the subject's face. The farther away you have your light source, the smaller the light is in comparison to your subject; light hits your subject at straighter angles, which causes sharper shadows. The closer you move your light, the bigger it is to your subject; light is able to hit your subject from multiple angles and soften your shadows (this is why huge softboxes make such nice, soft light on a person's face). Now, light falloff is still something you have to understand - but it really only affects the intensity (amount) of light hitting your subject - NOT the softness of shadows.

[@1mollymom]

Thank you for for this. I have always understood that the closer the light to the subject, the softer the shadows, and Peter's explanation that the further away the light to the subject, "the flatter the light" was confusing. Understanding the difference between contrast/sharpness and intensity is key.

[@FirstLast-il6ok]

Which means distance from light to subject is a matter of efficiency in light intensity as it pertains to inverse square law and nothing to do with "softness." That is a product of light source relative size (not necessarily distance) to the subject. Correct?@@ryandinan

[@alext9067]

Dynamic range of camera cannot follow that change. Look up gamma for film and TV. You'd be off the chart if you didn't stop up. You may have missed the point about the light intensity being more equal as the source is moved back. Take another look. Also, as for the rest of your comment: Shadows don't become sharper as the light source is moved back. They become sharper the smaller the source. It happens that moving something further away makes it look smaller, so bango. But we use large "Softlights" from any distance and the effect is minimal. If we need soft shadows and the light must be way back, we use more softlights. Your feet cast a sharper shadow for another reason. Look up "Umbra" and "Penumbra". Hurly is not trying to do anything but make a dry subject a little more zippy for non-tech students that would fall asleep if he was wearing a bowtie and putting numbers all over the screen. First rule in communicating: KEEP YOUR AUDIENCE AWAKE!

[@arunanand03]

Physics's light n optics was never misinterpreted before.

[@elmelmon]

I achieved that same affect with my flash on camera at weddings looking as if It were done in a studio. People always asked how it was done especially since they saw no back drops. It really made the dress of the bride pop with a black background. This is just to give you an idea of how and where to use this, you need to experiment.

[@justinleejamison]

One of the most informative and helpful videos that I've ever seen on lighting. Thanks so much for putting this together.

[@Americannorsk1]

I was thinking the same.

[@JoeOberster]

Correct me if I'm wrong, but it seems to me that as Peter moves the light source away from the subject, less light is reaching him. Peter then changes his camera settings to allow for more light to enter the camera. Therefore, at some point, he will be allowing ambient light from the studio and windows to enter the exposure (particularly the back of the subject's head) and the ambient light could be mistaken as flatter light from the strobe. Am I over-thinking this?

[@hozhenjie6755]

Which was what I thought too. That makes that demonstration useless. The last one however is the better illustration.

[@axisofpeter]

Light meters can detect the percentage contribution of ambient and strobe light, so it's easy to account for that. You might want some ambient exposure, especially as backlight. The general rule is that shutter speed controls ambient light and aperture controls flash. But that depends, I think, on the relative strength of ambient light and flash.

[@pietervandenberghe]

The back of his head can not be directly lit by the flash, it's just physically impossible. Question is: is the light on the back of his head ambient light, or flash light reflected from a wall or curtain behind him? In a room with no window light coming in, even f2.8 1/200th ISO200 will give very little ambient exposure, so my guess would be it's reflected flash light, which in turn would further illustrate the whole inverse square law theory (because the distance is then flash to reflective surface and back to subject). If he had just increased the flash power step by step instead of opening up the aperture, there would have been no doubt...

[@enricht]

I think that's less the ambient, as much as the flash's light is bouncing around the room, and lighting him.

[@RTKBAND_]

Light Meter Logic!

[@hawg427]

We had to learn this back in 1978 when I got my 2 year photography cert. in Daytona. Old school stuff works :-)

[@steveurmah]

So good. Big kudos to fstoppers and Peter for showing us the ropes!

[@Dominguezucv]

I personally find this video THE BEST video explaining Inverse Square Law!!!

[@nadeemafzal8984]

Many thanks Peter Confess never had a clue about the fall off concept Finally also get the dark background bit That also means moonlight and sunlight have zero fall off for my photography purposes ...

[@sevenbridgesoneriver4838]

They say the most intelligent people are those who can take complex subjects and make them understandable to the layman! Thank you so much, you just did what SO MANY of those on KZbin cannot do, you made this entire subject simple to understand and for that you sir are the best thing I’ve seen on KZbin Barr NONE!!!!! 👍🏽🙏🏽⭐️⭐️⭐️⭐️⭐️

[@jgarcia2013]

The effect on the models face is highly influenced by the angle of incidence of light rays. In the first shot, light source is so close to the model's face, that it's blocked from reaching the ear. It's misleading to think this effect is due to "light fall-off".

[@fregerreyes7080]

correct.

[@medqenmedness229]

Yes i think the instructor got a bit carried away there

[@duanevigue1603]

@@medqenmedness229 Well, its Peter Hurley, so yeah, he got a bit carried away. lol

[@MrVangassen]

I'm not a fotographer just trying to learn something to take better pics but thought exactly same thing. Thanks for confirming this :)

[@wolfamri]

Absolutely and at 9:12 Peter says that he can see the back of his head. You wouldn´t see that if it was outdoors in a pitch black environment - that´s bounced light. I really think people doing this kind of stuff should better plan their videos. For beginner photographers these guys are gurus, they should be aware of that and not confuse people for the purpose of being spectacular.

[@IsmailKhan-qx5gw]

Its amazing tutorial on KZbin... U hv cleared my concept about the variations of light from distances Love u and thank u dear,,, thumbs up

[@TeaToeKuu]

As a Radiology student, this is very helpful.

[@clivebrincat88]

07:54 : you said it got softer, if any it got harder as the light source is smaller relative distance from subject.

[@andyraeber6044]

Simple and easy to understand. Thanks Peter

[@rolandonana7864]

The best and short inverse square law course and demonstration ever !!! Thanks so much Peter

[@SamLyn]

Peter Hurley is the best!

[@maryw8720]

with all due respect, the first part is technically correct but the second demonstration part has incorrect information, the reason why you see more including the ear is because the light got a chance to disburse more over distance and the angle of incidence of the light changed. if the light was a perfectly cylindrical beam, his ear would not have shown in a perfectly non reflective dark studio. the quality of the light changes, yes, flat vs harsh, true, but not the ear stuff.

[@freshprinceofsolair]

@@enrique-hi not the ear stuff bra. not the ear stuff

[@Myfyrbyrd1]

I completely agree with you. The first demonstration is correct. The second demonstration should have used a wedged shaped piece of material such as wood or foam with a slight texture (facing the pointy side of the wedge towards the light source). This would teach the concept of light fall-off without the shadows cast from the face on the ear.

[@GStraveller-nr3eo]

skip at 6:00 if you are impatient😄 great video!

[@JimmeeAnimAll]

I'm in the middle of the video and I'm stunned with love and wisdom and I can't wait to share it back. Thank You very much for sharing

[@cmichaelanthonyimages2197]

Light is a constant, as far as its output at any one setting, using flash. The light application has so much to do with your total look for diffused highlight and diffused shadow...hence its control. Size and distance effects your background. Shutter will also effect its falloff. To really teach this, do it in a small studio with total light control. Not every photographer can move the subject 6 ,8 or 10 feet or more to effect different color gradients for their backgrounds. When I learned inverse law, I learned it with using multiple lights. Key here, learn this and you can overcome anything in a controlled studio. This is a must, and whats sad, many photographers do not know of this law or of the angle of incident light theory. They don't understand incident vs reflected light.

[@Myfyrbyrd1]

At time stamp 00:07:50 (2nd shot, light source further away from the model) the instructor says “starting to get softer”. I’m confused… I thought this may cause a harder shadow line when moving the light source away from the subject or model.

[@Nonixification]

jeh thats very confusing indeed

[@user-oc6mr1jr6s]

This is for the bare flash only i think. Not a flag in a softbox as an example

[@Rielestkid]

Been shooting for years now and haven't found a clearer explanation of this, well done. Wish he would've thrown in size of light source relative to subject detail also. Thank you for this!

[@kristamay4190]

He's trying to say that moving the light further away will soften shadows, but it's actually the opposite. Take a look at the first photo he took of the female model with the light far away, at 11:07, and the last photo with the light closest to her at 14:17. Note the difference in how sharp the shadows are below her nose and chin. He proved that moving the light closer to her actually softened the shadows. What was happening with the male model was a change in the size of the light source in relation to the subject, which is directly part of the inverse square law, but Peter didn't explain it. The light being further away allowed it to spread more before it reached him, which is why we get the wraparound to the back of his head. The closer the light source, the more brightness you'll see, but the less area you'll cover. The farther away the light (at the same power), the less intense the brightness will be, and the more area it will cover. This definitely has helpful tidbits, but if you'd like to be more familiar with the actual inv. sq. law, watch a few more videos.

[@FStoppers]

Moving the light away from your subject increases the sharpness of the shadow line but does "soften" or lighten the shadows themselves. This is magnified even more when you are inside because the walls, even if far away, start to act as fill to help lighten those shadows as well. -P

[@reality150tv]

Thank you to the model, I am not sure if they are getting paid or not for stuff like this. I watch a lot of youtube and all these models sit patiently while they explain and experiment for our viewing pleasure. Obvi thx to the photographer and fstoppers also.

[@adship3501]

Best explanation I have seen!

[@cowboyyoga]

Super video! And thanks for sharing a free 15 minutes! This is a very helpful video! )))

[@chrysmarty4935]

Struggled with this for awhile. Best explanation and now I get it. Thank you.

[@african3974]

Super informative...definite sub keep it up guys

[@shahriarabdullahsiddique4925]

What kinda meter is that you're using for determining aperture??

[@maxmac1394]

thats one of the greatest vid about lighting

[@rajeshpandey4131]

So so nicely explained. Thank you

[@bbdean6306]

What a brilliant explanation. Thanks so much Fstoppers.

[@RodAllsopp]

Awesome stuff! Can't believe people clicked thumbs down on this.

[@joandooley5245]

Very Helpful! info "clicks" visually and mentally Thank you!

[@a.krishna3924]

What if I want something on 7:02, but softer?

[@karenm853]

Huge. Don’t have the math gene but thank you Peter Hurley for simplifying this concept. Im a visual learner so this was excellent for me!

[@xXTrickLeagueXx]

The invers square law only works on omni directional light. If you focus the beam the falloff effect is reduced. If the light is focused like a moving head beam there is barely any falloff. Same if you use reflectors or parabolic umbrellas, the light is focused and will not have as much falloff. A softbox witch throws the light 180 degrees will have more falloff than a parabolic umbrella or reflector.

[@axisofpeter]

Do you have a source for that? Not only have I never read that, but my experience seems to contradict your contention.

[@kirkelicious]

With focused light you have to extend the light rays to where they would converge. This focal point creates a virtual light source behind the physical one. From this point of origin you can calculate the inv²-law. A Laser for example will have no falloff at all in ideal conditions. A snoot or grid will not change the focal point, whereas light shot through a fresnel lense of your hot shoe flash or a parabolic reflector like a beauty dish will. Simple physiks. Humans do not experience light intensities linearly, so the inv²-law does not correspond to our intuitions. As a guideline it works well though: Move your light source further and you will have less falloff. The higher falloff of a softbox is mitigated by its overall softer light and moving it further away makes it more of a point source again. That explains your contradicting experience. The inv²-law is only one part of the overall equation. But it is a good starting point.

[@pietervandenberghe]

A softbox starts out by throwing out light in a wider angle from its outer diffuser than say a 20deg grid, so the intensity or quality of both might be different at a given point, but light falloff from both sources will still obey the inv sq law between two given points. As I understand it, the idea of 'higher or lower' falloff has no value here.

[@DavidBichoHasBeard]

@@kirkelicious So few out there that have the ability to put this straight like this. You truly nailed an effective explanation. Hat off!

[@mariomifsud1302]

Excellent explanation.

[@bleuswiffer]

Awesome tutorial Peter and model!

[@zigzack54]

what is that device thats helping him chose F speeds?

[@johnbrennan2164]

One of the best explanations I’ve seen, thanks! Notice the shadow cast from your arm while writing? Hard shadow to low contrast ~you can make another video on that.

[@kinesis28]

Just too good, brilliant video.

[@brucelrenz8646]

Extra! Merci pour la vidéo. On en veut plus !

[@vadimyakus]

One of the best light tutorials our there. Period.

[@ecoral5635]

Amazing tutorial. 15 min of gem, thank you...

[@mohammadkhaledi1182]

Thank you .. excellent information about light and shadow..

[@outofthecommonphotography5503]

I don't shoot portraits. But, this is extremely good to know because I'm an actor and light myself. I've always had the light source very close. I'm really blown away at the distance being the secret for better illumination, to some degree. I mean there is more too it since the light source will be constant and not a flash. I'll experiment with it. Regardless, this is still just fun to know! :) Thank you for the video!

[@BrianHallmond]

This tutorial was awesome!!!!!!!!!!!!!!!!!!!!!!! I never realised that distance meant so much. I thought it was all about angle. Ive been working in a tight space so I never thought that would make a difference.

[@samarkandaljaberi1530]

Very good information..thank you 😊

[@philscomputerlab]

That was very interesting, thanks!

[@rellvilleterrace]

It’s crazy that a lot of these videos I had 2 watch twice in a 5 year span

[@DRI1966]

Your theory and practical exercise make this video one of the best one I have seen on this subject. THANK YOU

[@guiguigodro]

My mind went boom 🤯. This is going to help me a LOT with photobooth flash lightning.

[@jaimemunoz1059]

Man..that was a really good tutorial !!!!! Thanks !!!

[@gusy6129]

I used to do this with a flash light on the wall as a kid. Did not know there was a theory of this. Very nice.

[@brodi81]

Subbed after seeing this video. Super glad to see someone breaking down photog exp in math vs just "It's just how it works". Thank you so much for this video.

[@InMission]

Great, I love it, I never did any studio photography, so I didn't know about this concept, but actually, it helps to understand better the light in landscaping and street photography. Thanks, Really Appreciate.

[@oreste6076]

Where does the calculation begin? At the light source or at the last diffusor?

[@adnan.a.nazzal]

Amazing practice 👍

[@R2d2koko]

This tutorial giving a very good explaination ab inverse square law . Tq

[@Treviso100]

Two important things he didn’t mention: moving her away did cause the background to go darker, however, that is all contingent on the ambient light in the room and his shutter speed. Also, the closer that light got to her face the softer it became. This of course is due to the size of the light source in relation to the size of the subject.

[@allthecommonsense]

First guy's head becoming lighter also was the result of modifying the camera exposure to let in more ambient light. He isn't very good at explaining things.

[@sojourntheworld]

Wow 😯, that was sooo useful!!! Thank you

[@jw7903]

omg literally changed my life knowledge

[@minddropadam]

Such a great video! I'm in awe of the knowledge and insight I just gained within that 15 minutes! Felt like I experienced an epiphany!

[@princeilo]

so cool... need to see the full version. BIG THANKS

[@fandangofandango2022]

Great Lesion.

[@strel933]

Could you please share a video about metering, how to learn that? Xx

[@georgegatuz5411]

Kindly which meter reader are you using?

[@Methodical2]

Since many of you don't think he explained/demonstrated this correctly, can either of you do a video showing how it's suppose to be done? Or do any of you have a video showing how it's supposed to be done? If so, please link to it. I'd like to check it out. Thanks.

[@cineoitoum]

This is so cool to learn! I am just learning how to shoot with flash, and other day I was in a situation where the light was too strong on the subject. So I reduced the potency of the flash, but If I had watched this class before I would just put the flash one or two squares behind. Thanks!

[@amyw4816]

this is amazing, thanks so much for sharing

[@tonyjames5444]

'When a surface is illuminated by a point source of light the intensity of illumination at the surface is inversely proportional to the square of its distance from the point of source'. That's the Inverse Square Law word for word, basically if you double the distance of the light source from the subject the subject is receiving four times less light. That's to big a jump so an extra set of apertures were introduced i.e. f2-f4-f8-f16 becomes f2-f2.8-f4-f5.6-f8-f11-f16.

[@a.krishna3924]

Is the distance always measured by feet? Or it doesn't matter?

[@m.sifflet9443]

That's a good concrete way to explain it!

[@user-oc6mr1jr6s]

What does the inverse square law do to light from a bare flash when moved far back? I understand the light fall of but how is light softness affected? Is the light equally soft or hard when moved further away?

[@FStoppers]

Light always gets harder as you move it away from your subject. A barebulb flash is so small to begin with that it might not make a huge difference compared to a larger light source but it always gets sharper and harsher. The intensity and falloff are always under the inverse square law. -P

[@aklivn49]

AWESOME VIDEO!!!

[@denishaddad9359]

You cannot bend light. You see the back of his head at 9:42 because the light is hitting the surfaces in your room and bouncing back. Try that on a completely black room. I bet the light on the back of his head won't be so visible. Remember that different black surfaces will also reflect light to an extent. Regardless. That would be an interesting watch. Thanks for the video.

[@jamesallen9803]

Very concise! Thank you!

[@LeoInterHyenaem]

…and the Canon EF 100mm L2.8 IS L Macro - had one for a few years - just sold it today to finance My new gear acquisitions. A lovely lens, too.

[@ashtonrichardson3667]

What about the power of the light? Wouldn’t power and distance play a role. For instance if the light is a stronger source it could travel further without losing as much light as a weaker source? The only reason I’m asking is I’m just curious for the outdoors ambient light.

[@allthecommonsense]

A stronger light will be brighter than a weaker light IF both of those lights are the same distance from the subject. However... the percentage of REDUCTION in light intensity will be the same for either light across the various 1 foot intervals. It's a law of physics.

[@KINGFLAME360]

What power is the flash at? Are you using it TTL?

[@fotoPrzygoda]

Great video and great Subject!

[@spaghettitexan9514]

Very cool explanation!

[@sonidaso127]

Sweet Info! Thanks!!!!..

[@MrMarclauren]

Awesome tutorial

[@paintballmonkey666]

Thanks, I will definitely be using this.

[@RunNGunPhoto]

Great knowledge here, thanks for sharing some laws of light.

[@vemasphotography817]

Hai bro how to calculate the amount of light to set f numbers

[@davydao6765]

Good job !

[@DileepreddySobhaKrishna]

Awesome teacher.Hatsoff

[@DatzAdam]

You guys are amazing!

[@incredblethings9575]

What was the reading he was taking there? would anuone please explain that to me?

[@curtisbrooksmediapro]

Excellent!!!

[@JMARTx27]

Great video! Appreciate the knowledge!

[@MrThend]

So helpful! Thank you

[@xesse1]

Instead of moving the light away to lift the shadows, could you not just use a fill light? Would you be able to tell in a photo if they've used a second light or if they've just moved the light backwards?