What Leonardo da Vinci design used mirrors to concentrate sunlight for heat?

Leonardo da Vinci designed a solar furnace that used mirrors to concentrate sunlight for heat.

His proposal arranged reflecting surfaces so that sunlight could be directed toward a small target area. Concentrating the rays increases the energy delivered to that point, producing much higher temperatures than ordinary sunlight spread over a broad surface. Leonardo considered such concentrated heat for practical processes, including melting or working materials.

The design reflected his studies of optics, geometry, and the behaviour of reflected light. It was a conceptual high-temperature device rather than an industrial furnace demonstrated at the scale of a modern solar tower.

A solar furnace differs from a sundial. A sundial uses the Sun's position to indicate time, while a solar furnace uses reflected sunlight as an energy source. Modern solar furnaces use large arrays of mirrors and can reach temperatures high enough for materials research.