Soulburn Studios Art Lessons

Skylights, Domelights And Ambient Occlusion
By Neil Blevins
Created On: Nov 9th 2004
Updated On: Mar 13th 2026
Software: Blender or 3dsmax (vray)

Ambient Occlusion is a calculation that takes any particular point in a 3d scene and figures out how occluded this point is by the objects around it. Many 3d renderers use Ambient Occlusion as part of its Skylight calculation. A Skylight (also sometimes called a Domelight) is a light emitted from a sphere or dome around your scene (like the real sky), and then after the ambient occlusion value is calculated for a point, the light value is multiplied by the occlusion value to give you the final light intensity. The result is an evenly lit scene with soft shadows (or darkening) in cracks and crevices and under objects, much like how shadows look on a cloudy day.

Here's a render using a white Skylight with no other light source.

Frequently when using a Skylight, you don't emit a solid color like white, but instead you place a sky texture map (frequently an HDRi, or High Dynamic Range Image) in the skylight, so the light hitting your objects is based on the color and intensity of your sky bitmap, like in this image...

Let's do a deeper look into how ambient occlusion is calculated and then give some examples in popular 3d programs.

How Ambient Occlusion Is Calculated

First, lets pick a point we'd like to render. Lets call this point A. Next, the renderer shoot out a number of rays from A in a hemispherical direction around the face normal (since it's a ground plane, the face normal is pointing up), and it see how often these rays are occluded by nearby objects. So in this example, we shoot out 5 rays (in a real render we generally shoot way more than 5 rays, but I'm choosing 5 for simplicity). Rays 1, 2 and 3 do not hit any object on their way up to the hemisphere. Rays 4 and 5 hit a nearby object (the sphere), and so these rays are occluded. So in this image, we shot out 5 rays, and 2 are occluded, so our ratio of occluded rays vs total rays is 2/5.

Now lets look at point B, which is closer on our plane to our sphere. We shoot again 5 rays, ray 1 and 2 are not occluded by anything, 3, 4 and 5 hit the sphere and so are occluded. So this point is given a value of 3/5.

Now imagine doing this again and again, point after point on the ground plane. For each point we take the ratio of occluded rays over the total number of rays. The closer this value is to 0, the less it's occluded, the closer to 1, the more occluded it is. So in the example above, point A would be closer to black (less occluded), point B would be closer to white (more occluded).

In our 3d world, that gives us the following image...

Now multiply the light intensity of our Skylight (lets say the skylight color is a desaturated blue) by the inverse of the ambient occlusion image, and we get the expected skylight image.

Note: the actual math behind implementing this technique is far more complex, and each renderer does it a slightly different way, but this should give you the basic idea.

Blender Example

Unlike other 3d apps, Blender doesn't have an obvious Skylight light type, so this tutorial shows you how to make one. Here's the shader for Blender...

NOTE: You need to either use Cycles, or EEVEE with Raytracing on. If you use regular EEVEE, it will not render occlusion shadows.

Blender also has an Ambient occlusion shader...

This gives you an ambient occlusion pattern that can be attached to the material of an object without providing a light source (skylight / domelight). It has many of the same parameters as a skylight, but one of the big differences is in inclusion of a Distance (maximum distance value). This specifies a cutoff value for how far to shoot the ray before declaring it's a non occluded ray. This is useful for doing ambient occlusion indoors. But since a skylight is supposed to be a simulation of a sky, it does not include this parameter. This causes some confusion between what a skylight does, and what ambient occlusion is. So as a rule of thumb, a skylight / domelight is a light that includes an ambient occlusion calculation generally with no max dist parameter, whereas an ambient occlusion shader just provides an occlusion image with no light, and generally has options such as a max dist value.

3dsmax (vray) Example

Vray in 3dsmax has its own light type, set it to "Dome" to get a skylight.

Vray also has an ambient occlusion shader...

This gives you an ambient occlusion pattern that can be attached to the material of an object without providing a light source (skylight / domelight). It has many of the same parameters as a skylight, but one of the big differences is in inclusion of a Radius (maximum distance value). This specifies a cutoff value for how far to shoot the ray before declaring it's a non occluded ray. This is useful for doing ambient occlusion indoors. But since a skylight is supposed to be a simulation of a sky, it does not include this parameter. This causes some confusion between what a skylight does, and what ambient occlusion is. So as a rule of thumb, a skylight / domelight is a light that includes an ambient occlusion calculation generally with no max dist parameter, whereas an ambient occlusion shader just provides an occlusion image with no light, and generally has options such as a max dist value.