Among other things, digital capture and post-production have created a more thoughtful and sophisticated approach to light.  We have always seen a real-life scene in quite a different way from a recorded image, but before digital the options for reconciling the scene with the image were limited.  So limited, in fact, that there was little point worrying over fundamentals like capturing the entire tonal range of a high-contrast scene, or trying to bring together the different color casts from mixed-light scenes.  Now that we can get close to the individual elements of the visual experience, we need to remind ourselves what these are.

First and foremost, the eye builds up an image with unconscious rapid movements, flickering over the scene to take in first the most prominent parts,then the remainder, using a narrow angle of focused view.  This happens very quickly, taking a fraction of a second at the start, adding more information over time.  From the point of view of light information, the effect is that a huge range of brightness can be absorbed and factored into the view.  A single exposure onto film or onto a sensor cannot come close.  Instead photography has, over the years, established a syntax that includes silhouetted images and flared views.  These are artificial constructs, in that we don’t actually see in this way, but they are so familiar now that they have acquired a reality of their own.

Secondly, the visual cortex adapts to changing light conditions.  As daylight gradually fades to night, we do not experience increasing darkness until quite late on, thanks to various mechanisms including dilation of the pupil.  Equally, if you are sitting in a tungsten-lit room (such as ordinary light bulbs create) as the daylight fades coming in through the windows, and the room lights gradually start to take over, the color of the light will not seem to change much, yet if you were to walk indoors from the evening light outside, it would instantly look orange, or possibly yellow.  Any digital correction must be based on whether the viewer expect indoor light to have a warm tinge.
The human eye accommodates for major difference in brightness as well, by rapidly building up a “memory” of a view, flickering across it according to what catches its attention in unconscious saccadic movements.  The focused areas are relatively small, but “build” to a complete view, with brightness and color automatically equalized.
Most light we see by and photograph by is incandescent, which is to say it is generated by something burning.  This, though not much else, is what the sun and a domestic lamp have in common.  The important differences for photography are how big and how hot.  On another principle altogether are lamps that rely on passing an electric current through an enclosed envelope of gas to excite electrons into emitting light.  These have wavelength gaps in the emission that produce color casts—to which the eye can adjust much more easily than the camera and sensor.  Flash, a mainstay of photography lighting, is not part of our visual experience, being too rapid to register and image on the retina.

Stay tuned for more on photography, light and the digital sensor.

Richard Seymour

www.jargra.com