"Shadows in the Material environment are cast by a key light and ambient light (and should be a combination). In Android and iOS development, shadows occur when light sources are blocked by Material surfaces at various positions along the z-axis. On the web, shadows are depicted by manipulating the y-axis only. The following example shows a card with an elevation of 6dp."


Light Sources

Light comes in from all angles in the UI environment

University of Michigan - Ann Arbor

In the Material Design environment, the UI illuminated by virtual light sources called key lights and ambient lights. Material surfaces cast shadows when they obstruct light sources.

Light and Shadows

Material Design Documentation

Light

"Shadows provide cues about depth, direction of movement, and surface edges. A surface’s shadow is determined by its elevation and relationship to other surfaces."

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