This study tested the effect of photophase duration on black soldier fly, Hermetia illucens (L.; Diptera: Stratiomyidae), development. Successful larval eclosion, development time and adult emergence were measured for individuals exposed to 0 h, 8 h, and 12 h of light, at approximately 27°C and 70% relative humidity. Accumulated degree hours (ADH) were calculated to correct for differences in temperature across treatments. Larvae successfully eclosed in all treatments, with larvae in 12 h light requiring 5.77% and 4.5% fewer ADH to eclose than larvae in 0 h and 8 h, respectively. Overall, larvae in 0 h required 39.34% and 37.78% more ADH to complete their development from egg to adult than larvae in 8 h and 12 h, respectively. The effect of photophase duration on juvenile development was largest in the post-feeding stage, and smallest in the pupal stage. Specifically, post-feeding larvae in 0 h required 80.02% and 90.08% more ADH to pupate than larvae in 8 h and 12 h, respectively, but pupae in 8 h required 9.63% and 7.52% fewer ADH to eclose than pupae in 0 h and 12 h, respectively. Lastly, larval mortality was significantly higher in 0 h, with 72% survivorship, and 96% and 97% in 8 h and 12 h, respectively. However, 17.8% of mortality in the absence of light is hypothesized to be a result of predation by Arachnidae and Blattidae. These data could prove valuable for optimizing industrial processes for mass-production of this species for use as alternative protein in feed for livestock, poultry, and aquaculture.