The energy is converted from short wavelength (visble light) to longer wavelengths (infrared). A Dyson sphere would act as a black body [1] and radiates energy

The energy is converted from short wavelength (visble light) to longer wavelengths (infrared). A Dyson sphere would act as a black body [1] and radiates energy at the temperature of the sphere outer surface. 1. https://en.m.wikipedia.org/wiki/Black-body_radiation https://en.m.wikipedia.org/wiki/Black-body_radiation