The chemistry of light examines the work of Dr Theobald Palm. After his graduation from Edinburgh University, Palm joined the Edinburgh medical mission and was sent to Niigata in Japan where he remained for 10 years. During this time he noted the absence of rickets (a disease rife in Britain) in Japanese children and instituted a survey from which he deduced that sunlight deficiency was implicated in the aetiology of rickets. Unfortunately, he was largely ignored by the medical world. This paper seeks to contextualize his work. By placing Palm's study within a historical and social framework, its reception can be explained more easily.