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Working with lights in the 3D world

From: CINEMA 4D Essentials 4: Materials, Texturing, and Lights

Video: Working with lights in the 3D world

When the first computer programmers were developing 3D software they quickly realize that they did not have the computing resources to accurately describe how light behaves in the real world. Because of that, they subdivided how lights behave and gave us a variety of tools to simulate how light behaves in the real world. What light does in the real world is that it bounces, and in 3D software, by default, lights do not bounce. And that's true for just about every piece of software. There's only a very few special instances where light does bounce, and even that bounce is a simulation.

Working with lights in the 3D world

When the first computer programmers were developing 3D software they quickly realize that they did not have the computing resources to accurately describe how light behaves in the real world. Because of that, they subdivided how lights behave and gave us a variety of tools to simulate how light behaves in the real world. What light does in the real world is that it bounces, and in 3D software, by default, lights do not bounce. And that's true for just about every piece of software. There's only a very few special instances where light does bounce, and even that bounce is a simulation.

What I have here is a very simple scene that we're going to use to illustrate two important concepts with lights in CINEMA 4D. First is the idea that lights don't bounce. Second is the idea that lights pass through your objects. So let me show you something. I'm going to add a new light to the scene, and the light type that I'm going to add is something called a spot light. A spot light is a directional light source that's contained within a cone. Anything that falls outside that cone won't be illuminated. So let's add a spot light to the scene. By default, the spot light shines along the Z axis, and you can see that if I hit Command+R or Ctrl+R on the keyboard that my light source is there, embedded in the ground.

It's not really illuminating anything. So let's take the light source and move it. I'm going to hit A on the keyboard to redraw the frame, and then I'm going to raise the light up and point it at this white card that I have in the scene. And let's bring the light source up. I'm going to hit E to get the Move tool, and let's move the light up. I'm going to drag it up on its Y axis, and then I'm going to orbit it around. So let's take the light and hit R on the keyboard and grab the Y handle and point it right at that card. You can see as I orbit it around this way, it hits the card.

Now using a white card like this is a common technique in photography, and photographers will shine a light onto a white card to give a much softer effect on their subject. Now, if I hit Command+R or Ctrl+R, when I render my scene, you can see that the light is not bouncing. The light is not coming off that card and hitting my word. The other thing you'll notice is that the light is coming out the backside of the card. It's passing through the card on the way. Let's move over a little bit so you can see that more clearly. I'm going to orbit up like this and hit Command+R or Ctrl+R. You can see, there is my light source passing out of the backside of the card and continuing on to infinity.

Now let's get back to our scene. I'm going to orbit around and drag with the 1 and 3 keys to get back to our scene. And that gives you a really good illustration of those first two concepts. Light passes through your objects and light does not bounce. So that begs a question: How do you simulate those effects? Well, to simulate those effects, you need to use multiple light sources, and you also need to adjust some settings on the lights. So let's deal with the light bounce first. Now, normally, if I were to shine a spotlight onto a white card like this, you would expect it to bounce off that card and illuminate the other objects in the scene.

So, in order to simulate that light bounce, we need to have a light source that's right here in the same location as the card, pointing the same direction as the card. So let's add a new light to the scene, and this time I'm going to add an area light. An area light is essentially a rectangle of light. Now you can make an area light any shape you want, but it defaults to be a rectangle. So let's add that area light to the scene. So when I added the area light to the scene, it's in the center of the world, and you can see the white rectangle that represents the area light. Now, I want to get this area light in the same location as my card, so in order to do that, I'm going to take the area light and parent it to the plane.

Then I'm going to go to the Coordinate properties and zero them out. So I'll select that and go 0, 0, 0 and then tab all the way through and then 0 out the rotation for the light. You can see that it goes to the same location as the card. And the other thing is that it's about the same size as the light circle that's hitting the card, so that's pretty good as well. Let's render our scene and see what that looks like. Command+R or Ctrl+R. So now you can see that we've simulated light bouncing off that card. It's spread out a little bit too far.

You can see that it's got a spread on it that sends it off in too far on the left and right of the card. The other thing you'll notice though, is that that light is shining all the way through the card and passing out the other side, and that's what's causing this black line here. The way the area light works is that it's a light that shines in both directions along its Z axis, and right underneath the light you always get this dark line. Well there's a really cool button on the area light that we can adjust to correct that behavior. So let's go to the area light, and then underneath the Details tab, at the very bottom, is this little button right here, Z Direction Only.

And that's going to have it shoot in the positive Z direction, right along this axis. Let's turn that on and hit Command+R or Ctrl+R. And now you can see that we're getting a much better behavior. We still have our light from the spot light passing out the backside, but the light coming off the card is being bounced in a much more predictable way. So, how do we correct this light coming out the backside of the card? Well, the way we do that is by going to the spot light and turning on shadows. In CINEMA 4D, light passes through objects until you turn on shadows. So, let's go to the General properties of the light and I'm going to go to the Shadow pull- down and activate Area Shadows.

When I do that--let's render again, Command+R or Ctrl+R--and now you'll see that the light no longer passes out the back side. Now our light is still bouncing off the card at too wide an angle, so we can go back to the area light and adjust the barn doors on the area light. So if I click on the Light and go to the Details tab, there is something called a Falloff Angle. The Falloff Angle is like a virtual set of barn doors. If you've ever seen lighting from a studio, you'll know that they have these things called barn doors, and barn doors sit on a spotlight and they control how the light falls off.

So this falloff angle is what's causing the light to spread out so much. By adjusting the falloff angle, we can tighten up the direction of the light. So I'm going to take the falloff angle from 180 degrees and let's bring it down, and let's bring it down, probably we'll start off with about 90 degrees, and then we'll render again, Command+R or Ctrl+R. And you can see, now it's behaving in a much more predictable way. We've got our light bouncing off the card, hitting the ground, and illuminating other subjects. And you can see, it's a little bit probably too strong, so I can just go back through and adjust that light. If I go to the area light and then I'll go to the General properties and adjust the Intensity, the Intensity controls how bright the light is getting.

Now, a very important rule is that you should never trust what you see here in the Editor window until you render. You notice that when I bring this down, you can see that the light is simulating, that it's going up and down here, but I really shouldn't trust that Intensity level. I'm going to go up to the Render icon, and at the very bottom is the Interactive Render Region. When I activate that, you can see I now get this rectangle around my objects, and this rectangle will update every time I make a change. Let's enlarge it just a bit, so it's covering our whole scene. And I'm going to raise the quality level up to 100%, so I get a better representation of the scene.

And you can see that it looks very different inside this window than it does outside the window, so let's take the intensity and dial it down a bit. You can see that now we have a better representation. The light would normally, in the real world, lose quite a bit of intensity as it bounces off of this card and spreads out. We can also go to the light source and open it up a bit. Let's go to the Details and adjust the Falloff Angle, and we're going to adjust the falloff by upwards, to let's call it 120. There we go. And that gives us a little bit better spread. So now we've got our light kind of simulating that bounce, and that's really what this is all about is simulating that bounce.

The last component of this simulation is shadows. You notice that we don't have any shadows down here in this area. You'd expect this light bouncing off the card to cast a shadow off the ball and off the type itself. So the way we do that is by activating shadows. The programmers gave us that ability because a lot of times you only want your shadow to come from a single source, and so you can turn the shadows off and on. So let's go to our Plane Light, the light that's bouncing off of our plane, and then underneath the General properties, we're going to activate the shadow type to be Area.

Area is the most accurate type of shadow you can draw, and so we'll turn that on right now. When we do that, you'll see that now our light starts to behave more correctly. And you can see we've got some issues with our shadow. First and foremost, we've got this kind of line passing here. Now, a very important thing: because we've got our light in exactly the same position as the plane, it is intersecting with the plane and CINEMA 4D does not like intersections. Most 3D softwares don't. When some two things are in exactly the same location, the software doesn't know how to resolve it, so what we need to do is to move this light out of the plane.

It's in exactly the same location, so let's hit E on the keyboard to get the Move tool and let's grab that light. So we'll take it and drag it out just a hair, outside the light source. And you can see, that fixed those horizontal lines that we were seeing down here, and now our light is casting those shadows. Now, normally light bouncing off a card wouldn't cast quite such strong shadows, so now we can dial the shadow intensity down. The way we do that is by going back to the light source and going under the Shadow properties and adjusting the Density of the shadow down. So let's take the density down from 100 to, say, about 50%. There we go.

And that's starting to feel a little bit better. So you can see, this process that we went through will give you an idea of the kind of process that you'll have to go through when creating lights in your scene. The idea is to keep in mind those two important factors: number one, light does not bounce, and number two, light passes through your objects until you turn on shadows.

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