Readers have complained about this, because Robb goes on at wonderful length and in great detail about each picture. There are three solutions, the first two of which are not really satisfactory. Buy or get from a library a book of the paintings. Go to the Carol Gerten Fine Art site with its three pages of Caravaggio's. Go look at the real thing.
All art loses in reproduction.
It can only be talked around. Whatever it is, Caravaggio's best work has it in abundance. And, whether you look at a picture in a book or on the Internet, that quality is not there. Read Robb's book. Then go look at the paintings, whichever ones are closest to where you live.