Create and copy new shaders and lights.
When you start a new scene, there is only the environment and one shader (the DefaultShader) defined (and assigned to all objects). You can create a shader (based on the DefaultShader) or light, or copy a shader or light that you have customized.
Shader#1 and Light#1 are not used explicitly as names; the first shader or light with a given name is implicitly numbered 1.
By default, shaders and lights are named sequentially as you create them: DefaultShader, Shader, Shader#2, and so on, and Light, Light#2, and so on. To avoid confusion, however, name all your shaders and lights as you create them. If you let the system assign default names and later combine two or more files, all shaders and lights will be renumbered to avoid duplicate names. It may then become difficult to distinguish shaders and lights by name.
See New Shader in Render > Multi-lister.
To create a light using the Multi-lister
See New Light in Render > Multi-lister.
See Copy in Render > Multi-lister.