# Light and depth

One lamp, high and to the left. Everything is raised, level or recessed, and a pressed part sits below the plate.

Foundation · Free · https://tactileui.dev/docs/foundations/light

## Four heights

Every part is at one of four heights relative to the plate. The drawing is a section through each; above it, the part itself, live.

The lamp is always above left. Highlights go on top and left edges; shadows fall down and to the right. A shadow that falls up, or a highlight on a lower edge, is a bug.

## Pressing

A key is a cap on a skirt. Pressed or latched, it moves down by exactly the skirt and swaps its shadows for the pressed set: a shadow inside the top edge, a little on each side, and a lit line below where the plate’s lip shows. A latched selector key, a checked check and a checked radio do the same. A pressed state that only darkens, or only draws an outline, is not pressed.

## The light never turns

Turn this knob. The ridges and the pointer rotate; the highlight on the cap and every shadow stay exactly where they are, because the lamp did not move. Anything new that rotates must split the same way.

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## No glow, no frost

Only lamps and lit displays glow. There is no blurred glass as a material and no frosted card: the only glass in the kit is a display.

## The full law

This page is a summary in plain words. The brain holds the law itself, in `light-and-depth.md`, written for an agent to follow. It ships with the Kit.