Diabetes mellitus includes type 1 and type 2 diabetes. Type 1 diabetes is an autoimmune disease affecting young people. Although several factors that worsen type 1 diabetes are known, information on the effects of blue light remains obscure. In this study, we investigated the effects of blue light irradiation on diabetes using mice with streptozotocin (STZ)-induced type 1 diabetes. Furthermore, we investigated the potential of selected compounds in rescuing the blue light-induced aggravation of diabetes. Blue light irradiation exacerbated type 1 diabetes. It activated insulin-like growth factor-1 and reactive oxygen species/caspase 3/apoptosis/endothelial-monocyte activating polypeptide II/neutrophil/neutrophil extracellular trap-associated cell death (NETosis) system signaling and increased the expression of angiopoietin-like protein 2 (Agptl2). These results indicate that blue light worsens type 1 diabetes by increasing NETosis production and the expression of Agptl2. Administration of pantethine or tranexamic acid prevented the blue light-induced worsening of type 1 diabetes by suppressing neutrophil production and Agptl2 expression. Our results provide insights into the effects of blue light on type 1 diabetes and highlight the potential of compounds that can be used in ameliorating such effects.