Gaffer & Gear 68 - Inverse Square Law & Grids

[@hewhohewho]

Andrew, I would really like to thank you for taking the time to shoot all these breakdowns. You have absolutely no obligation to share your experiences, yet you still enlighten us. It's such a shielded and tightly closed industry, every opportunity to learn about different scenarios apart from - obviously, each of our own jobs, is highly appreciated. You are a vauluable source of education. Thank you!

[@bj0ernaa]

Damn.. Never thought about the "blindspots" close up that the grid creates.. This was super helpful!

[@jefffitzgerald5396]

Another great video! Since you're being lit by a smaller surface area of light up close, does that mean subjects closer to the source are also getting hit with a harder light than they would be from the same position without the grid?

[@Mr_G]

@@jefffitzgerald5396 No, because the angle by which you a lit stays the same regardless of the distance from the grid.

[@karmapolice3335]

wow thanks for this sir..u teach better then my film school teachers.

[@meetthegaffer]

Great episode! You explained it so much better than I did:)

[@AllTheBeef]

Solving this problem is something I've been struggling with for a while now. This help was invaluable. Never stop making these videos haha

[@jkattz1]

This video is a incredible explanation, as someone who has learned how to gaff overtime through moving up in the chain of electric/learning from every DP and other gaffers I have worked with and never really having a mentor these videos have been a absolute godsend

[@davidmultimedia2024]

Thank you so much for this episode! Very helpful! I learned A LOT and will definitely practice using these methods!

[@DavidBichoHasBeard]

Hat off. This is SO valuable information jammed in here. Super clear about ISL (loved that extra graph you pulled up), using the near-occlusion-effect in grids are VERY rare to see some one talk about on KZbin (double grids for even more effect) and you are the second person in my 25 years of lighting that mention that the f-stop scale follows ISL, and can be easily converted into any measurement (feet/meters/pizzas..) for quick and very accurate adjustments. 10/10 episode.

[@KacperSlonina]

Out of curiosity, how would you convert it to meters? Simply use 1.4m instead of 1.4f doesn't seem right, whereas going 1.4f = 1.4*0.3m seems to be quite a hussle to calculate in a hurry.

[@johnpaulporitz]

Hi Andrew, hope you're well. I really enjoyed this video. You spoke frequently of the technical constraints which dictated side light for the dance troupe. I found that so interesting. For me it would have been the dance troupe which dictated side light all other things be damned. I spent more than a few years after high school working in a 500 seat theatre which frequently hosted ballet companies. We always side lit the dancers for the sake of presenting the dancers' bodies as the model forms of athleticism they were. There was never any question about that. It's just how it was done. Granted, we were lighting for the human eye, not a camera, even so the end customer is the same. I'd love to hear more about how you coordinated with the live event crew on lighting. Lighting for a mixed audience (in house and at home) is rarely done beautifully. Be well, John Paul

[@silhouetteproduction4618]

Agree, i always like to place the light further away to maintain the natural transition of the light, i didn't know why, but now you are perfectly explained. Love it!

[@ilijastjepic4251]

Hi, I am huge fan of your channel, and don't buy a light unless you recommend it. I think everyone is wrong with why this works, would like to hear your thoughts. Inverse square law applies to the point light source emmiting in all directions, it is basically calculation of the sphere surface size based on the radius (distance). Light doesn't loose energy, it just covers the bigger surface of the sphere. Any directional light (45% and narrower) would fool ISL, as it is not spreading the same way as the point light would, but bigger lights would do it better. Directing the light basically moves the light source to where it would be if it was a point source, considering size and angle of light. The bigger the light and smaller the angle, it "moves" the source further away. If you move it by 3 meters, you eliminated the worst part of the ISL. The video of you while moving away from the light is perfect visual presentation of this. Without the grid that undirected light would hit the first line of dancers and nothing else, by blocking that light you directed the rest of it, and moved the light source further away. That's why adding grid drops the light level near the source drasticaly, and by a small amount further away. So it doesn't really work because you are lit by more lights as you move away, but because you get much less undirected light when you are close to the light. Still waiting for forza 500B review. :)

[@thanelovers]

I have a question about the inverse square law. Let's say you are able to move the unit farther back, either from finding more distance or using mirrors- but you want to use the LCD trick and have the diff closer to the talent. Would the light be falling off from the distance of the source, or would the diffusion cloth act as the new source and the light would fall off from that distance? I am not sure if the question is clear enough but I am happy to clarify. Thanks!

[@gaffergear]

The distance from the cloth, that is the light source lighting your subject.

[@ottawamountainman]

Great video. Correct me if I’m wrong but the correct term is “occlusion”; the principle by which the exposure of a subject decreases as a gridded light source is moved closer to the subject (effectively working opposite to the effect of the inverse square law).

[@gaffergear]

Yes!!! When we were filming this a whole group of us on set were trying to remember the term all day. Thank you.

[@ottawamountainman]

Gaffer & Gear I think the term first appeared in “Set Lighting Technician's Handbook: Film Lighting Equipment, Practice, and Electrical Distribution Paperback - Aug 2 2010 by Harry Box”. Thanks for making amazing educational videos. I do strictly photography (no video) but I’ve been studying lighting techniques from gaffers channels like yours. Cheers.

[@BushXCGL]

@@gaffergear but this phenomenon only works if the subjects are relatively close to the light source right? Because it seems that at the distance from which you were lighting them, they are all pretty much lit by the same amount of "mini light sources"...

[@gaffergear]

@@BushXCGL that's very true as the closest person to the frame would be at the closest 10ft. But because of the 90 degree spread of the individual cells, they are only getting hit with the full force of the cells that they are inline with. The rest do contribute, but not to their full amount, until you get a long way back. When we walked around the set it didn't feel like we were getting hit with everything off all the cells until we were near the middle of the floor. It felt to me like it was having a huge effect on the outside 40% of the dance floor only, the rest felt like the normal drop off. This of cause would be different with other grids, such as a 40 degree for example.

[@BushXCGL]

@@gaffergear "This of cause would be different with other grids, such as a 40 degree for example." Sounds like another tutorial incoming....XD Thanks for the reply Andrew. That's something to think about....

[@carlitoshuanes]

This is brilliant! I had never encountered the grid workaround. That makes so much sense once you explain it.

[@guyparsonage4148]

This is one of the best breakdown and informative channels on you tube - keep it up 👍

[@RynosDOP]

I love the pro tip at the end there about walking lights off in feet similar to f-stops. Insta sub

[@jeremyblaiklock4243]

Thank you so much for this channel, it's been an unbelievable help in growing my understanding of gaffing.

[@IAmAFilmDude]

What a great breakdown Andrew! Thanks for sharing your knowledge bombs & experience.

[@aeonsnarfus]

All wheat...no chaff. Superb.

[@pawelabe7542]

Hi! That channel is great, I am really a huge fan of it. The only thing that is confusing me a little, is the last part (dividing distance into f-stops): if we have a source of light on the left, an actor on the right (on Your image) - it is f1.4 on a lightmeter (we do not have a lot of light so we need to open an aperture). Than we are visualising being closer to the light, so a proper exposure should be f2.0, f.2.8, f4 etc., that's fine. But shouldn't the distances between the points be greater on the right (when we are far away from the light) than on the left (when we are close to the light - changes in light intensity are seen more quickly close to its source). Regardless, I emphasize that in my opinion this is a great channel, the amount of knowledge is huge, opinions on using grids are very useful. I keep my fingers crossed for continuing to create these videos, there is nothing better on yt in the topic of knowledge about light in film (in my opinion).

[@gaffergear]

@@pawelabe7542 I think in the next episode I explain, this seemed to confuse cinematographers. Point of reference is the light (because I'm a gaffer moving the light). Where as for cinematographers the point of reference is the subject you point the camera at. Opposite math.

[@hmbojalil]

Hi Andrew, Nice move add that grid! 👏🏼👏🏼👏🏼👏🏼 I always did it with screens and flags, but this is a great solution! Thanks for share! Happy 2020!

[@gaffergear]

Yep, I used to have a forest of nets

[@DanCunningham-d7k]

If it was a tighter shot on the talent like a bust or waist shot and grip gear or time was limited AND there were no objects or background in frame for light to spill on and change in brightness, I might start the talent in a brighter spot of the beam and as they were advancing gradually pan them into the dimmer beam edge IRT. You can simulate them passing under street or interior lights or oncoming car lights by doing something opposite. As they "pass under" the light, pan the hot spot toward them briefly. The fun is finding quickly what you can do to pull the gag off and move on to the next shot. So many ways to solve so many things.

[@NeonDarkShadow]

Phenomenal video, Andrew! You just taught me a number of things I’ve been completely unaware of, or wrong about for many years.

[@99SBX]

Brilliant! Thanks for the education.

[@nicklarovere]

holy cow, this is so valuable... mind blown please keep teaching us!

[@CineMilledUSA]

Loved this explanation on the use of grids! Great stuff

[@Rom2Serge]

OMG. I newer thought this way about the grid. Thank you.

[@Dodosimch]

Such a great and intuitive explanation of the Inverse Square Law!

[@IslandFilmMaker]

This lesson was amazing! So exciting to see work on this level! Thx to ALL that made it HAPPEN

[@thelightpainters]

Thank you very much Andrew. Sharing a ton of knowledge as always with your videos. Thanks again!!

[@JeffersonDonald]

Brilliant. Highly educational and very informative. Thanks for this. And truly hope to one day say to you that the first round is on me. Cheers.

[@simonsen7621]

You're awesome. A big hug from Brazil.

[@tristangates2797]

I've done a bit of both lighting and sound in live production, but have been watching your series to learn a bit more about film production, great stuff, and loving your channel. Talking about the light fall-off being logarithmic is something that I knew, but it brings up something that is commonly a part of audio sources: it's 4pi*r^2 for a point source (the area of a sphere), but lines and planes actually have lower falloffs. For instance on an infinite line, since that would be the area of a cylinder it would be 2pi*r^2, with a finite line being somewhere in between. The falloff for an infinite plane then has even less fall off, with a finite plane again, being somewhere between an infinite plane and a line source. So it seems to me that in general just making the area of the light-source a large area (in this case with diffusion), should reduce the fall-off even without the use of a grid. Am I thinking about this correctly? Has this matched your experience? That equation for line sources may also may be useful knowledge with the proliferation of linear LED light sources. Also, as an aside, I didn't know that F-stop was a logarithmic scale. It turns out that one F-Stop is about 6dB. Maybe just trivia for most, but for me it helps my understanding.

[@LostandFoundTravel]

Thank you sir - yet again.

[@Rkitcey]

Cheers for the great grid/inverse square detail. I’m loving your quality content. I only recently discovered this channel, and I’m catching up quick, so I apologize for the late comment. @Gaffer & Gear One thing I didn’t notice either mentioned or diagrammed - and sorry too if it’s outside the scope of this channel, but it seems related - was the fantastic mottled lighting reflected from the camera movements by the dance floor surface treatment. This element raised the polish on the whole production for me off into outer space. Could you please comment on the floor treatment, and how it was implemented? For me, it seems like serious gaffer’s wizardry, and I can’t imagine this commercial having been shot so great without it - thanks!

[@juandiosdado]

Absolutely brilliant! Wish I could give it 100x thumbs up.

[@TJ-TJ]

Really good teaching mate! Keep it up!

[@ChuckDotson]

This explanation is AMAZING. Thank you!

[@AlexLopez-iy4by]

Great lighting and thank you for excellent breakdown.

[@loudandclearmedia]

Whoa. Mind blown. I cant wait to try this out!

[@cameranerdsmedia]

Super helpful video! Thanks so much

[@cobralyoner]

Very helpful! Thank you so much Andrew!

[@Danielleessmith]

Great episode 👏

[@euchian]

Thank you so much for all these information! Really grateful!!!

[@icandi9178]

That's beautiful, man!

[@davidminard]

Awesome! Had no idea! What was the shiny floor material? Dry but reflects like wet and isn't screwed up by friction from all those feet!

[@gaffergear]

I'll see if I can find out. It was extremely experience.

[@gaffergear]

It's a specialist dance floor called harlequin

[@davidminard]

@@gaffergear Thanks for looking into that! You rock!

[@Praxiszooms]

WHAT A GREAT TRICK (with the grid)

[@RCVelezWasHere]

Very useful information :)

[@GlennHanns]

Hey Andrew, love your channel! Just wondering what’s your favourite diffusion material for passing light through for softness and most transmission?

[@gaffergear]

I like grid cloth, I use 1/4, 1/2 and full.

[@SashaRadovanovic]

This is gold! Thank you 🙏

[@ensanchefilms8645]

Wow! Super useful tip the one of the grids.

[@claycar]

Thank you. Excellent tutorial

[@wsfvn]

Thanks for your great explanations ! Take a bow :)

[@adepew]

Thanks so much for this great explanation!

[@visualsmugglers]

Hello, love this, better than any film school, i've got one question thought so. Why do you put the gels on a frame and away from the light, what is the difference between having a gel on a light to on a frame? Also how much distance do you give it? Thank you!

[@gaffergear]

These lights are so big they melt the gels.

[@visualsmugglers]

@@gaffergear thank you for answering that, that makes total sense now.

[@matoflynn]

Absolutely brilliant, thank you! Subscribed!

[@anton_cine]

superb, mate! Thank you for this

[@JADURCA]

Incredibly Great!!!!

[@reynoldsc]

Thanks very much for that Andrew it was very well explained!! In terms of the lighting for the interior, I'm guessing that there was no way of lighting from the front by hanging lights and diffusion? I realise that you had to get the crane in but could the crane not have swung under the lights thus not casting any shadows? Again, many thanks for taking the time to share 👍🏻👍🏻

[@gaffergear]

My first thought was to do that. One of the reasons for side lighting, not covered in the video, was a transition shot where the camera goes into the chest of the dancer and then pulls to the beach scene. This was shortlisted before filming. In the BTS you can see the crain very close to the dancer for this shot. About 14:27 in the video. Shot is at 1:54, they wanted his chest to be black for the transition. The other reson was budget. The lighting gantry is about 4 floors up on that sound stage. And we only had 90 minutes set up time as we couldn't afford the studio for a set up day. We also only had the budget for one best boy and me. Originally we also wanted the back lights up in the gantry. But we couldn't afford the rigging, so we elected to stick them in shot. I did have skypanels with octodomes and grids on standby to add light from the front, just in case the grids didn't work on the 12x12s. So I had a sleepless night beforehand as prior to the shoot, this was untested theory for me, and no body I knew had done it this way. We didn't expect it to work this well to be honest.

[@reynoldsc]

@@gaffergear Thanks Andrew that explanation makes perfect sense and again, cheers for taking the time to reply. I hear you about the 'sleepless night' btw.........I guess it comes with our territory!!!

[@navidnadjafi8442]

That was great👌🏼 Thanks

[@chrisfreiboth4606]

thank you, great stuff

[@OppaiDaisukiful]

OMG all this time i was using inverse square law in a wrong way. I'm so glad that i found out your channel, more gaffer should aware of this law so they don't guessing the distance to move the light. is it possible to use it with meters tho ? i'm not get used to it when using imperial unit. i'm also using lux reading than foot candle

[@gaffergear]

I have just made a follow up video to explain it more clearly, should be up in a few days.

[@gaffergear]

You can use any units of measurement, I often visualise car parking spaces, One gaffer who lights huge battles visualises soccer fields for distance. I work in stops, never got my head around lux and fc. No one here in Australia used either. DPs never ask me for lux, could me a.melboune thing.

[@OppaiDaisukiful]

@@gaffergear thanks man looking up for your next vid

[@renebohmer3206]

This might be a stupid thought but wouldn't it be possible (let's say you don't have the space to move the light further away) to just use big mirrors to lengthen the way the light travels?

[@gaffergear]

100% yes

[@birkgroven9160]

Would a grid also keep the subject lit relatively consistently soft until you get so far back that all the cells light the subject?

[@gaffergear]

Yes

[@modermaster]

wow great tip, tank you so much

[@frannyfranman]

Oh my god so many DPs and gaffers have explained this to me incorrectly. I feel like Neo when he first woke up from the Matrix 😭

[@raredreamfootage]

12:29 - Mind blown!!!!

[@shaukat863]

Very nice sir thank you for your👌😊

[@david_gaffer]

Genious

[@thekaiser4333]

Hello Mike.

[@raredreamfootage]

The sun is a good example of inverse square law. It is so infinitely far away that the earth looks to be uniformly lit.

[@gaffergear]

That's the example I use in class

[@zoom2027]

very useful

[@h4328]

dude you're awesome

[@RobbScholarTube]

You the GOAT

[@leoquesto9183]

So. Damn. Good.

[@jmez927]

here before 100k

[@Strravaganza]

The video is excellent, the dancing is gay.

[@gaffergear]

That made me laugh 🤣