Step-by-Step Pictures and Instructions To Build Floating Shelves

I want to use this method to build several shelves in a nook I have. I would be using 3 walls to anchor the shelf, not just one. The nook is 15" deep, so do you think that by using 3 walls I could accomplish building a shelf that was 50" wide, 15" deep and could hold a decent amount of weight (say a lamp and a toy box ,or a shelf of books)?

I would not place anything that is heavier than pictures. This design does not offer much support for heavy objects.

does anyone know how much weight this can hold? I want to use this method for a shelf of books... I read the article, but I am not sure if it is strong enough to hold up so many books...