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A more intuitive name for Inverse Square Clamped Light Falloff would just be to call it realistic falloff. Real world light uses the inverse square law in which the light is one-quarter of the intensity at double the distance. The word Clamped is in there to add that this calculation begins at the edge of the radius, so it's clamped to that starting value. Let's take a look. So here is a scene set with Smooth Falloff Lighting from the center and I am just going to change it, just so we can see the difference.
Immediately Inverse Square Clamped Lighting is going to do one thing. It pulled in a little bit, but it disperses more. So instead of falling off linearly from the edge of the radius, now it's using this special law. We have a Radius of about 540. you can see the hotspot there, and what you're getting here is just a more natural light. So you don't get control over where the edge of the falloff is, but you can of course adjust the Radius, which I'll do right here.
The light is called Clamped because it calculates beginning at the edge of that Radius, so it's clamped to that value, but really this is more commonly just called Inverse Square Lighting. Now, it's interesting to look at this in an abstract scene like this, but let's take a look at how it helps you if you're trying to match a specific real world light. Here's a shot that calls for a sign replacement. Now, to get this all ready and be able to light it in 3D, I went ahead and created a 3D camera track.
I will show you the keyframes. And this was done with the Foundry's excellent Camera Tracker plug-in. Now, you don't need to know that plug- in or even particularly need this camera data in order to do this exercise. You could instead just place it in your own 3D sign where it belongs. What this is doing is actually tracking it in place across the shot and it allows us to place the spotlight just above it. Right now not correctly set. In about the same place as the one light that's here in the scene.
I also added a shadow and the reason I did it that way as opposed to having this light cast a realistic shadow is just for simplicity's sake. I would have to create a building surface for that shadow to be cast on and that was just sounding way too complicated for a simple, basically drop shadow. So obviously this isn't matching now and even with good old After Effects lighting with no falloff, we could do a better job than this. So to begin with, I will just solo the source shot and I am going to want to get the things like the light color from that background.
So I will sample a color from the sign, say something like that, and I am going to make it a pretty hot, close to white, color, but just with a little bit of pink tint, because that's what I see happening in here. My guess is that this was actually probably a neutral colored sign and that the color is all coming from that light. That's what I see happening. Let me turn on the sign again just so we can make some adjustments to it, or rather unsolo the background layer. So I want to raise the Intensity of this light quite a bit, to get a little bit of that kick there.
And of course the shadows aren't really matching. So probably widen out the Cone Angle and maybe soften it a bit. And that's about the point to which we would be taking this with the old school After Effects lighting. Now let's see what we can do by adding Inverse Square Clamped Falloff. Now, instantly there is no change and the reason for that is that the Radius setting is very high. So in fact, there is no light decay happening at all. This slide is probably just about as big as this whole scene right now.
So I am going to bring it down a lot. I could hold down the Shift key in fact to get more quickly down to the values I want. Let me take one more look at that original shot. So what I see is a bright hotspot here and a pretty rapid decay. I am not necessarily trying to match it exactly, although if that was what I wanted to do, I suppose I could try for that, but I am just interested to find something like that effect, whether it's the bright hotspot, but then the natural falloff right from that.
Now any further adjustment I make, say to the Intensity, will also be reflected in that nice falloff, so I will try to match the hotspot and then just get kind of the throw of that light looking pretty natural, and this is very subjective. When I think I am ready to see it in motion, I can preview the shot. 0 key on the numeric keypad. And that looks to me like not a bad first effort. So Inverse Square Lighting offers a close simulation of how light falls off in the real world and a quick way to get more natural subtlety into a scene.
Now, just to take one more look, if we go back to no falloff at all, we still have a nice hotspot, but the sign is all flattened out and there's none of that nice decay of light that you see with this setting.
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