I just carefully looked at the web link you gave. And downloaded the actual test and figured out how it works. But this method is not really a glowing material. He is just a white lighted white board. Even according to this method can not do the effect of the TV screen. It's not even close to a real light-emitting material.

At the time I didn't know or forgot to mention it but for a glow effect you have to set illum to 0 in the MTL file.

I agree with you when you say “add a switch for white light source or not under gloss in the material modification options”. It's better than nothing, and Puybaret is sometimes too obsessed with “simplicity”. Puybaret is sometimes too obsessed with “simplicity” and ignores a lot of more critical real user needs.

There's also the transparency modification you mentioned in the link above. I mentioned it many years ago if I remember correctly. I don't know why sweethome3d hasn't added this important feature after all these years ~ it should be very simple to implement!

There's a reason for this: target audience and marketing. I agree that I would like to see all these settings in one or more dialogs but it would increase the difficulty of using the program for newbies. Imagine you have to start using Photoshop without having used any photo software before. As a beginner you would search for simpler software to start with. The same goes for Sweet Home 3D. I have grown into Sweet Home 3D over 15+ years and during that time many, many features have been added to evolve it from a simple home design program to what it is today. Would I like to see all these features added? For me definitely but it would make the software a lot more difficult for starters that might go looking for something more simple.
For not adding a transparency setting: the reason was that Emmanuel was afraid that users would randomly use the setting to set it for many materials and transparency greatly increases 3D and photo rendering times. Personally I would have added the feature with a display tip that warns for increasing processing time. I would also add a dialog to the Edit materials dialog to set the properties for light settings to a material.
But do this at 10-20 more places and Sweet Home 3D becomes as complex as for example Photoshop. So it is not really "obsessed with 'simplicity'" but keeping the program in line for the intended audience. I would add all the features but place them in sub-dialogs that a beginner can ignore. It is now up to Space Mushrooms to decide what the future of Sweet Home 3D is.