Laser light is coupled to optical fibers arranged in a sheet, which may be in the form of netting, mesh or fabric. Scattering centers or bends in the optical fibers allow the coupled light to escape from the sides of the fibers. Depending on the selection of wavelengths for the lasers, the resulting luminous sheet may be used for illumination of crops grown in vertical farms. The laser wavelengths excite plant photopigments for predetermined physiological responses, and the light source intensities may be temporally modulated to maximize photosynthesis and control photomorphogenesis responses. Each laser may be independently controlled, and at least one laser may emit ultraviolet-C radiation. The luminous sheet may be used for purification of air flowing through an air duct.