Caustics are the focused light patterns produced when light reflects off a curved surface or refracts through a transparent one. Familiar examples include the bright wavy bands on the floor of a swimming pool (refraction through moving water), the bright spot under a magnifying glass aimed at the sun (focused refraction), and the bright curve on a tabletop next to a wine bottle (refraction through the glass).
In architectural rendering, caustics matter for any scene involving water (pools, fountains, glass-floor features), wine and drink glassware on dining tables, glass facades or curved metal that focuses light, and crystal chandeliers. Caustics are computationally expensive in traditional rendering because they require carefully tracing many light rays through complex geometry — most general-purpose renderers either approximate them or disable them by default.
AI rendering handles caustics implicitly when the scene calls for them — wineglasses on a table will produce visible caustics on the tablecloth in the rendered output, for example. Explicit prompt direction like 'visible caustics from the wine glass on the table' or 'caustics from the pool on the wall' will push the AI to emphasize the effect. Without that direction, caustics often appear but at lower intensity than a fully-computed traditional render would produce.
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