I'm not saying the light source should be attached to the material. Now such light sources are also wanted. It's just that adding light sources to furniture is a pain in the ass and too much of a hassle for furniture library creators. That's why not many people in the world are willing to do that.

How is this difficult? In the Library editor you set a material name for the material that you want to act as a light. That's it. Nothing more to it.

About the power setting for each light source individually:
This was discussed before here: https://sweethome3d.com/support/forum/v ... 2755#60154 (Some remarks in that thread are no longer valid. Back then you had to manually edit the properties file in the zip to set the light source. That is no longer needed.)