An information processing system includes a storage, an interface device, and a computing circuit. The storage stores a database, in which spectrum data concerning light from a light source and a measurement condition data at a time of measurement of the light are associated with a plant status data concerning growth of a plant and/or a harvest data concerning a harvest of the plant. The interface device receives an input of a user measurement condition which is to be applied at a time of measurement of the plant by a user and which includes data concerning angles at the time of measurement and data concerning a plant status and/or a harvest to be predicted. The computing circuit determines at least two wavelengths contained in the light from the light source to be measured under the user measurement condition by referring to the database based on the user measurement condition.