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Light Direction

read the form, place the light

round
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score
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best
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Tracing light back to its source

Six forms make a round, spheres first and then lumpy blended shapes, with the contrast dropping and the sun’s height running to extremes as the round goes on. Each is lit by a sun you cannot see. You aim at it with two controls — the ring says which direction the light comes from, the corner arc says how far it is tilted toward you — while a small preview of the same form under your current light sits beside the real one, so the guess is a visual match rather than a number. Lock in, and the reveal shows the true sun and names the miss on each dial.

The picture is not decorated, it is computed: the form is shaded per pixel from real surface normals against a real light vector, and the cast shadow is that same form projected along the vector onto the floor under a declared 16° camera pitch. Shadow length therefore comes from the sun's true altitude — raking light throws a long faint one, an overhead sun leaves a tight pool — and it cannot contradict the shading above it. The shadow edge, where the light stops and the dark side begins, is the second cue; painters call it the terminator, the reveal labels it, and the sun lies on the line from there through the brightest spot.

Degrees off, and what they cost

Each form scores 100 · clamp(1 − max(0, angErr − 3°) / 42°), where angErr is the angle in 3D between the light vector you placed and the real one. Inside a 3° grace cone it is a flat 100; at 45° off it is zero; the round is the mean of the six. Those two constants hold on every device — what changes with your hardware is only how big the targets are, the ring reading ±34px under a trackpad, ±54 under a finger and ±58 for a pen. That expression is the whole marker: one angle between two vectors, computed here in the page. No model is involved in the score.

More value & light drills: Value Squint · Shade a Sphere · Value Thumbnail · the whole catalogue