Lights are of course necessary to see the meshes and affect brightness and colour. All meshes will be lit by a light unless specifically excluded from being lit. Light will pass through all meshes and will produce shadows only when shadow generation is set on the mesh. The default number of lights allowed is four but this can be increased.
There are four types of lights that can be used with a range of lighting properties. They are
The three properties of lights that affect are diffuse and specular which apply to all four types of light and groundColor, which only applies to an Hemispheric Light.
Overlapping lights will interact as you would expect with the overlap of red, green and blue producing white light.
Every light can be switched on or off by enabling or not and when on its intensity can be set with a value from 0 to 1.
For shadows a shadowGenerator object is needed. A mesh can then produce a shadow by adding it to a rendering list of the shadowGenerator. There is also an extension, shadows only, that allows shadows on a transparent mesh.
To begin to understand how meshes react to light you need to know about the normals of a mesh since they form part of the calculations in determining the color and illumination shown.
This post process effect can produce rays of light as scattered by the meshes it hits.