We’re going to talk about diffusion. We’ll look at how to use it. The different types used professionally and how you can create it with household materials.
What is diffusion? It’s the action of spreading light from a light source evenly so as to reduce glare and harsh shadows.
But first, we need to talk about why we want to diffuse light in the first place?
Where can we get an answer? One place to look is to the beautiful world around us.
Daylight coming in through a curtain. A room lighting someone through a doorway.
And Why? Because we like the effect and/or because we want lighting that fits into the geography of a scene they’re in.
Diffusion vs Harsh Lighting
So how do you create diffusion? A popular theory is you just put some white diffusion material in front of your light. But here’s the thing: diffusion doesn’t change the actual waves of light, it just creates a wider source of more scattered light. The size of your light source determines how diffuse it is on your subject.
You see, a small light comes from one direction relative to our subject. It, therefore, creates harsh shadows. It’s what we call a point source of light.
But if we shine that same light through diffusion, here this round silk that’s part of my 5-in-1 reflector, we now have a wider source of light. Light from the center, the edges, all of it, is lighting our talent. This wider source “wraps” around our subject more than a small, point source of light. It, therefore, fills in its own shadows.
Hot Spots and Filling the Frame
Now if diffusion doesn’t change the quality of light, why do some gaffers double up their diffusion. Even some softboxes come with an extra inner layer of diffusion. I’ve even had people tell me it “doubles” the softness of the light rays. Really?
Remember, the actual light rays don’t change. We’re just creating a wider source of light relative to our subject. So why double?
Let's look at that silk again. You’ll notice a hot spot. This means our the diffusion frame, as a diffuse light source, is uneven. Our subject will be lit less evenly by this frame.
Adding a second layer of diffusion can help us even out the spread of light from our light source, by creating a wider source of light that then illuminates our silk.
Another way to create an even spread is with what is called a book light. We bounce light into a card or reflector at an angle to our diffusion, here a sheet of Lee 216. The setup is like an open book, which gives us a more even spread on our diffusion frame.
Double diffusion and a bounce card do eat up some of our light output so we have to keep that in mind. Some diffusion material can eat up 1 to 2 stops of light.
Types of Diffusion
In the film biz, they use three types: silks, gels, and bounces.
Silk material is really nylon and it’s used on silk flags and frames.
You can buy this material online, link in the description. You can also use fold up silks as I did from my 5-in-one kit. You can grip them in a c-stand or use this handy device to adapt them to a light stand.
I like to use my round silk from my 5-in-1 kit with LED pars and for my fluorescents the larger oblong version.
Gels on a film set are generally rolls. They’re 4’ wide and 25’ long. They’re cut and taped to 4x4’ frames and other uses. Rolls are wonderful but expensive.
What’s the alternative? Gel sheets. They come usually 21”x 22” square but also come in other sizes like 10”x10.” You can buy them at your camera/video store or online.
Ask for a gel book like this, super helpful to actually see the gel material
But which gel diffusion should you use as there are a lot of them? Basically, there are two types, opaque and frosts.
Opaque’s are thick enough you can’t see through them and are best for creating wide diffusion sources.
The most common and popular on sets I’ve seen is Lee 216.
Frosts are more transparent. Think a thin cloud layer were you can still the sun or a frosted window. They maintain the shape and beam of a light but soften its edges.
Opal and Hampshire are popular frost gels used on sets.
Bouncing light is a form of diffusion. All this light in this room bouncing off the walls is diffuse light.
We can create our own by using 2x3’ showcard. You may be used to using a collapsible frame for bouncing sun or daylight as fill but you can also use it inside. Grifflon is a material used on bigger frames as a large bounce on exteriors.
The advantage of industry produced diffusion like 216 is it can handle the heat, especially when clothes pinned to a tungsten lights barn door. But with LED’s today and other low-heat lights like full spectrum fluorescents, heats not really much of an issue.
I’ve used a curtain panel from my Ikea Ritva curtains that I use on my windows. They’re $10 for a pair in the US.
You can also use tracing paper sheets like those used on china lanterns. And yes, you can use china lanterns but I only use them in a big space with high ceilings for ambient/background levels of light since they spread light everywhere.
I want max light output towards my talent so I use LED par bulbs that focus a lot of light in one direction, and that’s usually through my diffusion.
You can buy the same nylon “silk” material used in flags. I bought a 1 yard by 60” piece that’s perfect, for a little over $7 bucks.
You can also use the popular low budget diffusion used in the indie world forever: the shower curtain. It was so popular back in the day there used to be a gel sheet sold called shower curtain.
The curtains used are generally the liner and come in two flavors, opaque like 216 or frosted like opal. I only use the 216 lookalikes because if I’m using a shower curtain it’s because I want a big, cheap diffusion source. Frosted won’t give me a big soft source right.
Now one item we don’t have time to get into is containing all that spill from lighting diffusion. On set a 4’x4’ 216 frames would be contained by 4’x4’ solids, side, top and sometimes even the bottom. But on smaller sets with smaller crews, soft boxes come to the rescue.
They not only contain all the spill from your bulbs but the reflected interior sends it forward, helping to give us an even spread.
Now, this only touches on the main types of diffusion which is probably all you need. We don’t get into grid cloth, big 20 by silks and others. Future episodes. But if you play with these forms of diffusion, you’ll be fine. Shoot tests. Play around with different materials. And Would love to see them.
Do you need specific inside tips and info? Find out about our one-on-one consultation with Frank or Manu now.
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NEEWER 32-Inch Portable 5 in 1 Translucent, Silver, Gold, White, and Black Collapsible Round Reflector
Limostudio Reflector Disc Holder Clip
ALZO Diffusion Fabric Nylon Silk White Light Modifier, 1 Yard Long 60 inches Wide
by ALZO Digital
Lee 216 Filter sheets White Diffusion 24x21"
Lee Opal Filter sheets White Frost Diffusion 24x21"
Lee Filters diffusion page
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