Faking Sunlight

Or: making your light global without Global Illumination ;)

Today we're going to talk about a easy-to-use technique also known as the "lightdome". To get started, take a look at the two images below:

The left one looks dull and flat, while the right one give's a nice impression of depth and volume. The reason for this is (as always) the light setup.

To understand the usage of the method outlined in this tutorial, let's think a moment about light in an outdoor environment. It primarily comes from the far, far away sun. But that's not all (that's why I said "primarily"). As the light approaches the atmosphere a big part of it doesn't makes it right through but is heavily scattered (ouch ;) ). Not enough, as the light hits any surface it is deflected with more or less loss of its energy. Voil, secondary light ;)

So when the light has finally made it through to our object (the car in the example above) a big part of it has a totally different direction than the light that has left the sun.

So why not turning the ambient light up, one may ask. Simple: ambient light can't cast shadows while the reflected light in our environment does.

As I said before, the secondary light comes from nearly all directions around the object in scope. "Nearly" because the light becomes darker (looses more energy) as you increase the difference from the original direction. In other words, you will have nearly no light coming directly from the bottom (and "nearly no" here means no visibile difference if you totally ignore the light directly from the bottom).

Ok, enough of this physics stuff, let's set this up. Note: The technique will be shown in 3dsMax but any rendering package which has point lights, directional lights and softshadows will do fine. We assume the scene set up and we already have our primary directional light (the sun).

Front view

Top view

If we render the scene now we come up with the left picture at the beginning of the article.

Now we place a point light exactly at the center of our scene with the following settings:

The reasons for these settings will get clearer as we go on:

With the pointlight still selected go to the hierarchy tab and hit the "Affect object only" button:

Move the pointlight high above your scene. Now we've left the center of rotation to the center of the scene but moved our light on top of it:

Now, with the front view selected, go to Tools, Array and set up an array with a 30° rotation around the z-axis, five elements and "Type of Object" set to "Instance". This will give you the possibility to modifiy your settings later without the need to setup anything from the beginning. Do the same with the angle for the array set to 30° and we end up with:

For better handling, select all the pointlights and put them in a group.

Now change to the top view and again- go to Tools, Array. Leave the angle as is, but increase the count in "Array Dimensions" to 6.

There's our lightdome. Adjust the lightsettings and scaling as needed and you should end up with an image like the right one at the beginning.

[Grab the zipped tutorial here (103KB).]