After serving as a pharmacist's apprentice, Swan became a partner in a chemical firm that manufactured photographic plates. At that time, one of the most difficult steps in the production of photographic plates involved adding chemicals in a liquid state to the plates. However, Swan discovered that the fluids used on the plates became more sensitive when carefully heated. This meant that the plate could actually work better when dry. By 1871, Swan had developed the much simpler "dry-plate" photographic method. His innovation initiated a new era in photography, leading to rapid improvements over the next 20 years. Swan also invented the first bromide paper, which is still widely used for printing photos.

Swan's primary interest, however, was electric light. Recalling the days of his youth, when indoor lighting was dim and expensive, Swan observed that "as a rule, the common people went to bed soon after sunset." Swan began...