Abstract Precise temporal and spatial control of gene expression greatly benefits the study of specific cellular circuits and activities. Compared to chemical inducers, light-dependent control of gene expression by optogenetics achieves a higher spatial and temporal resolution. Beyond basic research, this could also prove decisive for manufacturing difficult-to-express proteins in pharmaceutical bioproduction. However, current optogenetic gene-expression systems limit this application in mammalian cells as expression levels and induction degreeupon light stimulation are insufficient. To overcome this limitation, we designed a photoswitch by fusing the blue light-activated light-oxygen-voltage receptor EL222 from Erythrobacter litoralis to the three transcriptional activator domains VP64, p65, and Rta in tandem. The resultant photoswitch, dubbed DEL-VPR, allows an up to 570-fold induction of target gene expression by blue light, thereby achieving expression levels of strong constitutive promoters. Here, we used DEL-VPR to enable light-induced expression of complex monoclonal and bispecific antibodies with reduced byproduct expression and increased yield of functional protein complexes. Our approach offers temporally controlled yet strong gene expression and applies to both academic and industrial settings.