Painting with light

Caravaggio's method was to abandon most of the canvas. One high, hard light falls on the figures and everything else is surrendered to a brown-black that swallows the walls, the floor, the depth of the room. His contemporaries found this vulgar and said so, and they were right that it was a shortcut: a dark background is a background nobody has to paint, and difficult anatomy can simply be dissolved.

It is also, unarguably, the most efficient way ever found to make a flat surface hold volume. The eye reads a form as three-dimensional from the transition between lit and unlit, not from outline, which is why a Caravaggio hand reaching into the light is more convincingly solid than any amount of careful drawing.

Vermeer, working in the same century from the opposite direction, was probably using an optical device — the evidence in the paintings includes exaggerated foreground blur, points of light rendered as soft discs, and a tonal accuracy that is very hard to achieve by eye alone. Whether or not he traced anything, the pictures show a painter looking at a projected image and painting the light rather than the object.

In 1839 the process reversed. Instead of a painter observing light and reconstructing it with lead white and umber, light was made to deposit its own image on a silvered copper plate. The daguerreotype needed exposures measured in tens of seconds under bright sun, which is why early portraits show people braced in clamps and why the streets in early photographs are empty: anything that moved did not register.

What the plate could do, immediately and without effort, was tonal accuracy — the exact business the painters had spent three centuries learning. What it could not do was colour, and would not for a long time. For half a century the most accurate images available to Europe were monochrome, and the culture adjusted to reading value alone as a full description of the world.

Early emulsions were not neutral in the way the eye is neutral. Orthochromatic film was sensitive to blue and green and effectively blind to red, and the consequences run through every photograph and every film shot before the 1920s. A blue sky renders as blank white paper. Red lips and red dresses go nearly black. Freckles and blemishes darken; faces need heavy makeup in unnatural colours to photograph as skin.

Cinema inherited the same limitation and worked around it in set design and costume, choosing fabrics for how they photographed rather than for how they looked. When panchromatic stock arrived and finally saw the whole spectrum, faces and skies changed appearance across the industry within a few years — a shift in the look of films that had nothing to do with anyone's artistic intentions and everything to do with what the emulsion could register.

German Expressionist cinema in the 1920s took Caravaggio's arrangement and made it a system: a hard key light, no fill, deep shadow used as an active part of the frame, and sets built with the shadow painted onto them where the lighting could not be trusted to produce it. Film noir in the 1940s inherited the whole apparatus, and it survived partly for the same reason the technique had spread through Baroque workshops — a set that is mostly dark is faster and cheaper than a set that is fully lit and fully dressed.

The result is that a genre remembered for its moral atmosphere was in significant part shaped by schedules and budgets, which is not a reduction of it. Caravaggio's tenebrism came out of a working method too. The style is what happens when a constraint is used deliberately instead of apologised for.

The modern version of the dark room is a grading suite, where the light in an image is adjusted long after it was recorded, and where a scene can be pushed from noon to dusk without anyone returning to the location. The trade is the same one photography made in 1839: enormous control over the reproduction of light, at the cost of the physical event that produced it.

What has not changed is the underlying grammar. A bright area on a dark field draws the eye and everything else recedes. That fact is doing the same work in a Caravaggio altarpiece, a wet collodion portrait, a noir interior and an interface with one lit call to action — four technologies, four centuries, one piece of human wiring being used over and over.