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Photochemical reactions are the reactions that are induced by light. Many of these reactions are found in natural processes, including photosynthesis and the formation and decomposition of ozone in the atmosphere. Classroom demonstrations are effective in enhancing students' learning and retention. Herein, we have developed a simple demonstration of a photochemical redox reaction, which can be performed in a classroom or laboratory setting in schools and universities. This demonstration can be performed in both traditional and active-learning formats. A light-yellow solution containing ferric chloride, 2,2'-bipyridine, and sodium pyruvate, when exposed to visible light, produces a pink color that can be discerned within 3 min. The same reaction mixture kept in the dark does not produce a change in color, indicating that light is essential for this reaction. In the presence of light, pyruvate ions reduce ferric ions to ferrous ions, which then form a complex with 2,2'-bipyridine molecules, resulting in the production of a pink color. The intensity of the pink color increases with time, indicating the accumulation of products. This demonstration is simple, does not require a special source of light, and gives an excellent example of a photochemical redox reaction.