Jan Ingenhousz is the figure most widely credited with discovering photosynthesis as a light-dependent process. He showed that light is essential for plants to restore the air by releasing oxygen and that only green plant parts perform this gas exchange, building on Joseph Priestley’s earlier work (which showed plants restore air in general) and on experiments conducted in the 1770s. Ingenhousz published his key results in 1779, establishing that photosynthesis requires light, that green tissues are the active sites, and that plants respire (release carbon dioxide) in darkness as part of their metabolic balance. These insights laid the groundwork for understanding how light energy drives the synthesis of organic matter from carbon dioxide and water in plants.