DIN resp. DIN-norm is the abbreviation for “Deutsches Institute für Normung” (engl. German Institute for Standardisation). DIN stands for a voluntarily developed standardized standard of material and immaterial objects.
The DIN EN-62471 (equivalent to the European guideline 2006/25/EG) determines what the criteria for grading a light source are resp. what endangering might result. The assessment is not only for the emitted light.