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There are a number of ways of simulating indirect lighting within a mental ray render. Indirect lighting is essentially the lighting that occurs when photons of light come out of a direct light source, such as this directional light, bounce off its surface, and hit another surface. So the secondary lighting effect, the light we see on the other surfaces, that is known as indirect lighting. So if I render this scene, what you're going to see is there's a direct light source coming through the hole in the top of the room.
And it's hitting the surfaces within the room and how the shadow is turned on, so we can see the shadow cast right here on the sphere. We can also see that there is no other lighting in the room, because there's no indirect lighting. This whiteness that you see in the roof, I've turned that on by going to the camera settings, and in the Attribute Editor for the Camera1 Shape, I've gone down to the Environment and set the Background Color to white. So I've just basically turned the slider all the way up. The only reason I've done that is just to make a little bit more obvious in the render where the light is coming from.
It's not actually going to affect the lighting in the scene when I'm using global illumination. So the first thing I'm going to do is to create some global illumination. I'm going to create a point light and drag it up in the scene, so you can see it right there. This light is only going to cast indirect lighting, so I can actually set the Intensity all the way to zero. I don't need to worry about shadows or anything like that. I just need to turn on Emit Photons in the mental ray Caustics and Global Illumination settings. So I'll just turn this on.
I've noticed that with Maya 2011, sometimes you need to click this on a couple of times. The next thing I need to do is go to the Render Settings, and in the Indirect Lighting tab of the Render Settings, turn on Global Illumination. Now, that I've done that, I'm going to open the Render View, store this, and create a new render from the same camera. You immediately see the difference. We were seeing indirect lighting. All this lighting you're seeing on the walls is created by global illumination, including all the colors.
So that is essentially how you activate global illumination. So you'll notice that the global illumination effect created by the default settings is not terribly convincing or realistic. But that's okay. Now that we've activated a global illumination, the next step is play with the settings, so that we can get a more realistic and visually pleasing render.
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