Turning the Screen Down

A brightness slider does not dim an image evenly. Cut the backlight to a fifth and the highlight comes down with it, but the shadows were already sitting only a few steps above black, and those steps drop below what the eye can still separate. The floor of the picture goes first: a photograph that held detail in the trees at full brightness turns into one dark shape.

What happens next depends on the panel. An LCD leaks a little backlight through its black pixels, so a dimmed screen renders the dark areas grey and faintly milky rather than empty; an OLED switches those pixels off and keeps the black, then has to work to hold the near-black steps apart. The eye changes shift too — rods take over from cones after dark, and red dims before blue does — so the same file reads cooler and flatter at night.

The wallpapers that survive the evening are built on middle tones: fog, overcast light, a wall in shade, a dusk that refuses to go fully black. Keep the deep-shadow frames for a bright room. On a screen turned down far enough to read by, a picture with somewhere to sit in the middle keeps most of itself.