It is interesting that, if you think about it, a picture doesn't end at its frame. That is why looking at a picture on your computer, and the same picture in a museum can provoke different emotions. Your computer screen is surrounded my what ever is on your wall, but art in a museum is often purposefully lit, with the architecture of the room and surrounding artworks that frame the mind.
Caravaggio was a renaissance painter who used light and shadow as characters in his compositions. His style can be described as chiaroscuro - literally 'clear' and 'dark'. I might have underestimated how dark his pictures can be when seen in their intended setting as opposed to in a book or on a screen.
I recently had the opportunity to see a Caravaggio close-up. 'The calling of St Matthew' is one of three Caravaggios in San Luigi dei Francesi, a church in the center of Rome. An image ripe with metaphor and foreshadowing, the Christ figure points to call a reluctant disciple with a hand that closely resembles the hand of God in Michelangelo's 'creation of Adam' (physically located just across the river in the Vatican). The Caravaggian twist is to place this hand in a dark room with tax collectors in 17th century dress rather than a fantastical scene of clouds and cherubs.
What is interesting is that, though the picture is lit in the church with artificial lights on a coin-operated timer, when the light goes out the painting is only lit by a small window on a nearby wall. In this natural lighting, the painting is so dim, the mid-tones of the painting become part of the deep shadows. All that remains are the brightest parts of the image.
There is significantly more scuro than chiaro in the real world setting. The reproductions in books are trying to preserve the details of the picture at the expense of the shadowy reality of the physical space around the original.
The remaining highlights show the artist's focus in the painting - the had of Jesus, the perceptiveness of the youngest boy to the event, the cross-frame on the window. The bowed head of Matthew is so dark it can barely be seen. The light is not on him yet. Perhaps if the scene was painted a few seconds later...