(For more resources related to this topic, see here.)

Basic light sources

You use lights to give a scene brightness, ambience, and depth. Without light, everything looks flat and dull. Use additional light sources to even-out lighting and to set up interior scenes. In Unity, lights are components of GameObjects. The different kinds of light sources are as follows:

• Directional lights: These lights are commonly used to mimic the sun. Their position is irrelevant, as only orientation matters. Every architectural scene should at least have one main Directional light. When you only need to lighten up an interior room, they are more tricky to use, as they tend to brighten up the whole scene, but they help getting some light through the windows, inside the project. We’ll see a few use cases in the next few sections.
• Point lights: These lights are easy to use, as they emit light in any direction. Try to minimize their Range, so they don’t spill light in other places. In most scenes, you’ll need several of them to balance out dark spots and corners and to even-out the overall lighting.
• Spot lights: These lights only emit light into a cone and are good to simulate interior light fixtures. They cast a distinct bright circular light spot so use them to highlight something.
• Area lights: These are the most advanced lights, as they allow a light source to be given an actual rectangular size. This results in smoother lights and shadows, but their effect is only visible when baking and they require a pro-license. They are good to simulate light panels or the effect of light coming in through a window. In the free version, you can simulate them using multiple Spot or Directional Lights.

Shadows

Most current games support some form of shadows. They can be pre-calculated or rendered in real-time. Pre-calculation implies that the effect of shadows and lighting is calculated in advance and rendered onto an additional material layer. It only makes sense for objects that don’t move in the scene. Real-time shadows are rendered using the GPU, but can be computationally expensive and should only be used for dynamic lighting. You might be familiar with real-time shadows from applications such as SketchUp and recent versions of ArchiCAD or Revit.

Ideally, both techniques are combined. The overall lighting of the scene (for example, buildings, street, interiors, and so on) is pre-calculated and baked in texture maps. Additional real-time shadows are used on the moving characters. Unity can blend both types of shadows to simulate dynamic lighting in large scenes. Some of these techniques, however, are only supported in the pro-version.

Real-time shadows

Imagine we want to create a sun or shadow study of a building. This is best appreciated in real-time and by looking from the outside. We will use the same model as we did in the previous article, but load it in a separate scene. We want to have a light object acting as a sun, a spherical object to act as a visual clue where the sun is positioned and link them together to control the rotations in an easy way. The steps to be followed to achieve this are as follows:

1. Add a Directional light, name it SunLight and choose the Shadow Type. Hard shadows are more sharply defined and are the best choice in this example, whereas Soft shadows look smoother and are better suited for a subtle, mood lighting.
2. Add an empty GameObject by navigating to GameObject | Create Empty that is positioned in the center of the scene and name it ORIGIN.
3. Create a Sphere GameObject by navigating to GameObject | Create Other | Sphere, name it VisualSun.
4. Make it a child of the ORIGIN by dragging the VisualSun name in the Hierarchy Tab onto the ORIGIN name.
5. Give it a bright, yellow material, using a Self-Illumin/Diffuse Shader. Deactivate Cast Shadows and Receive Shadows on the Mesh Renderer component.

   
6. After you have placed the VisualSun as a child of the origin object, reset the position of the Sphere to be 0 for X, Y and Z. It now sits in the same place as its parent. Even if you move the parent, its local position stays at X=0, Y=0 and Z=0, which makes it convenient for a placement relative to its parent object. Alter the Z-position to define an offset from the origin, for example 20 units. The negative Z will facilitate the SunLight orientation in the next step.
7. The SunLight can be dragged onto the VisualSun and its local position reset to zero as well. When all rotations are also zero, it emits light down the Z-axis and thus straight to the origin.
8. If you want to have a nice glow effect, you can add a Halo by navigating to Components | Effects | Halo and then to SunLight and setting a suitable Size.

We now have a hierarchic structure of the origin, the visible sphere and the Directional light, that is accentuated by the halo. We can adjust this assembly by rotating the origin around. Rotating around the Y-axis defines the orientation of the sun, whereas a rotation around the X-axis defines the azimuth. With these two rotations, we can position the sun wherever we want.

Lightmapping

Real-time lighting is computationally very expensive. If you don’t have the latest hardware, it might not even be supported. Or you might avoid it for a mobile app, where hardware resources are limited. It is possible to pre-calculate the lighting of a scene and bake it onto the geometry as textures. This process is called Lightmapping, for more information on it visit: http://docs.unity3d.com/Documentation/Manual/Lightmapping.html

While actual calculations are rather complex, the process in Unity is made easy, thanks to the integrated Beast Lightmapping. There are a few things you need to set up properly. These are given as follows: